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Herd Immunity

Some infections can be eradicated from the face of the planet. Smallpox is the one example of disease eradication to date. Smallpox still exists in US and Russian labs, but there has been no wild cases since 1977.  It is, like the Dorothy, history.

Why were we able to eradicate smallpox?  Three reasons:

1) There is only one form of smallpox. Unlike influenza that changes from year to year.  So only one vaccine needed.
2) By what appears to be a once in a universe miracle, every county cooperated with  the WHO (much like we all cooperate with the IRS) so the entire planet received the vaccine. Once enough people were vaccinated, the disease was unable to perpetuate itself and spread and so died out.
3) Unlike bacteria, there are no asymptomatic smallpox carrier states.  Eradicable viruses usually cause symptomatic disease and do not result in asymptomatic, infectious carrier states that serve as a reservoir for infecting others.  HIV and Herpes cause chronic asymptomatic infections and will probably never be eradicated.

There are other diseases that are theoretically eradicable, like measles and polio. They have one antigenic type, have no carrier state and, if the entire world could be vaccinated, the disease would cease to exist in the wild.  I am sure there would be biologic weapons labs that would always carry a vial or 2 of every infection. Just to be safe.

Could we ever eradicate bacterial diseases? No way. Not ever.  Bacteria will often colonize people, not causing disease.  Neisseria meningitis, for example, will, depending on the season and the population studied, will be found asymptomatically in the throat of up to 35% of people (1). The asymptomatic carriers serve as a source of bacteria that can subsequently be passed on to others, who, for reasons of genetics or bad luck, develop invasive disease.

Asymptomatic carriage can be important to developing immunity to bacteria.  Like vaccines, carriage exposes the immune system to small amounts of antigen and can lead to immunity. Unlike vaccines, there is the small, but real, chance that the bacteria will become invasive and kill the patient. Or jump to another and kill them.

The meningococcal vaccine is not one of the stellar vaccines.  It has modest efficacy, but may make the difference between life and death in some patients.   The meningococcal vaccine can decrease the chance of an individual having invasive disease or dying from the disease, but perhaps more importantly, the vaccine can markedly decrease the asymptomatic carriage rates in a population (2).

The decrease in the number of disease carriers is vital to the prevention of bacterial infections. Vaccines are never 100% effective. Some people are genetically unable to respond to the vaccine, some have immunodeficiencies that preclude receiving vaccines or developing a response to the vaccine, some haven’t gotten around to vaccination or are too young to receive a vaccine.  If you vaccinate a large number of people, besides preventing disease in an individual, it helps protect the vulnerable in a population. Vaccines prevent disease propagation.

A recent example of beneficial  effects of the vaccine mediated decrease in carriers occurred with the conjugate pneumococcal vaccine that is given to children.  The conjugated pneumococcal vaccine is directed against the 7 most common disease causing strains. Pneumococcus is a nasty bacteria, causing pneumonia, sepsis, and meningitis.

The use of the vaccine lead to a decrease in the incidence of meningitis of 64%  for the vaccine strains in children less than 2 years old, but, due to a general decrease in the carriage rates in the community, the rates of meningitis also dropped in the greater than age 65 group by 54% and a decrease in meningitis for all ages by 73% (4).  The use of the vaccine in children has also lead to the decrease  in invasive pneumococcal disease in adults (3).

Herd immunity at work.   Part of herd immunity functions to decrease the number of people in a population who carry the disease so that an at risk population are not exposed.  Part of herd immunity functions by preventing the spread of some, especially viral, diseases.  If there are not enough vulnerable people in a population, the disease cannot spread and perpetuate.  However this mechanism for herd immunity is less helpful with bacteria, which can colonize or cause less obvious disease.

Like pertussis.

Pertussis, whooping cough, is caused by a bacteria, Bordetella pertussis.   It infects the upper airway of children, causing obstruction and intractable coughing and vomiting after coughing.  Kids can cough themselves to death, unable to stop coughing to take in a breath.  The whoop of whooping cough occurs when the kids cough themselves blue and rapidly suck in air so they do not suffocate. If you vomit while trying to inhale, as occurs with pertussis, the child can suck vomit into their lungs, a bad thing as Eric ‘Stumpy Joe’ Childs proved.

There is a vaccine against Pertussis and it has been effective in helping to almost eradicate the disease in the US. World Wide disease there are about 294,000 deaths from pertussis.  In the US disease  “the rate of pertussis peaked in the 1930s, with 265,269 cases and 7518 deaths reported in the United States. This rate decreased to a low in 1976, when 1010 cases and 4 deaths occurred (9)”.  Before the vaccine pertussis killed about 8000 children a year, a death rate of about 1 in 500 (10).
Pertussis cases have been climbing. There were, in 2007, 10,000 cases of pertussis in the US, a new record.
USA. USA. USA.

Those numbers are all well and good, but a moving picture is worth thousands of words.
Warning: children are suffering in this video.
http://www.youtube.com/watch?v=dZ5jf-5MobE.

This is what the vaccines prevent.  This what will come back as vaccination rates fall.

The vaccine is good, but not perfect. Vaccine efficacy is  64%  for cases defined by mild cough,  81% for paroxysmal cough, and 95% for severe clinical illness (11). Note the vaccine is good for attenuating the disease, not preventing it entirely.  Patient with a cough are very infectious.  Cough is a great way to spread disease (15).  The reason the doctor asks you to turn your head and cough when testing for a hernia is not that turning the head improves the hernia exam, it is so you do not cough on the doctor, a remnant of the age of Tb.   And immunity wanes with time, so older populations are at increased risk for having asymptomatic  disease (8)

Pertussis persists in the adult population, due to declining immunity over  time and primarily presents as a prolonged cough, not whooping cough. Adults have enough immunity to avoid the severe manifestations of the disease.  And pertussis is common.

“From September 1986 through February 1989, we studied UCLA students with cough that lasted 6 days or more  . During this 2.5-year period, we found that 26% of the evaluated students had pertussis and that illness was endemic throughout the study period. Similar studies  done in adults in the United States, Australia, and Germany have had generally similar findings. Twelve percent to 32% of persons with prolonged cough have been found to have pertussis. In our study, important clinical findings in persons with pertussis were that the median duration of cough illness before seeking care was 21 days, productive cough was rare, the most common clinical diagnosis was bronchitis, and in no case was the diagnosis of pertussis entertained (9).”

So there is a huge potential source of pertussis, omnipresent, presenting atypically, at least as far as whooping cough is concerned, ready to kill.  Maximizing immunity in children and boosting immunity in adults is the only way to control pertussis:  Herd immunity.

With pertussis, while herd immunity may help prevent disease spread, because it is a bacteria and can be present without causing illness, the  herd immunity rates required to prevent the spread of disease are much higher than needed for viruses.  Immunity rates needed to protect the population from pertussis are about 94%, while virus spread is decreased if immunity rates are only 80% or so.  More of the population can be vaccine slackers and not be at risk for a viral illness, but not pertussis.

As discussed in this blog, there are pockets of non-vaccination in California.  According to the LA times, over 10,000 kindergartners had vaccine exemptions and some schools had very high no vaccine rates, many over 20%.

So far, no big outbreaks, but pertussis is the one I would expect to hit first.  As it requires the highest herd immunity rates and the has the biggest source of potential sources, California is primed for a resurgence of pertussis. All you would need to infect, say, an entire Waldorf school, is one adult who comes to work with a cough.

Published in Pediatrics this month is a paper that looked at the effect of vaccine refusers on laboratory confirmed (PCR or cultures) pertussis in Colorado (13).  They had 158 cases of pertussis  in the Kaiser system between 1996 and 2007.

Infected children were significantly more likely to have parents who refused vaccinations  (11.5%) than the controls (0.5%). The difference translated to a 22.8-fold increased risk of pertussis in the unvaccinated children.

At the time in Colorado, vaccination refusal was less than 1%, but they accounted for 11% of the cases of pertussis.  That’s not surprising.  With a bacterial disease like pertussis, a small slip in the vaccine rate can lead to a big jump in disease.

The vaccine is not 100%.  So there will be cases in vaccinated children as well.  What is striking is ALL the cases in the unvaccinated group could be attributed to not having the vaccine.

Oh, that’s Colorado.  I don’t need to worry. Doesn’t apply to my community.

There have been natural experiments in the world where diseases that were rare due to immunization came back with a decline in vaccination rates. Like Sweden. Watch as immunity in the population falls, watch as pertussis comes back. On the count of three, everyone say duh.

“Immunization against pertussis was introduced in Sweden in the 1950s and discontinued in 1979. This was followed by a low endemic level of pertussis for 3 years. Thereafter the incidence gradually increased and there were two outbreaks in 1983 and in 1985. In the period 1980 to 1985 pertussis was confirmed by culture or serology in 36,729 patients of which 11% were younger than 12 months of age and 69% were ages 1 to 6 years. An estimate of the total frequency of pertussis in preschool children was made from reports from a sample of the child health centers. The annual incidence rate per 100,000 population ages 0 to 6 years increased from the 700 cases in 1981 to 3200 in 1985. The ratio of total cases to those reported from the laboratories was 3:1 in 1981 and 2:1 in 1985. The cumulative incidence rate by the average age of 4 years was estimated at 16% of the unimmunized cohort born in 1980 compared with 5% of the immunized cohort born in 1978. The seriousness of pertussis was evaluated by studying the 2282 pertussis patients hospitalized from 1981 to the end of 1983. Forty-eight percent were infants younger than 12 months of age. Neurologic complications were noted in 4% and pneumonia in 14% of the hospitalized patients. Eleven children received assisted ventilation. Fatal outcomes were reported in 3 children (0.1%), 2 of whom had severe congenital disabilities (8).”

Ready?
One.
Two.
Three.

Hey.  I heard that all the way in Portland.

Similar outbreaks of diphtheria, a bacterial disease that requires viral herd immunity rates of about 85% to prevent spread.  When the Soviet Union fell apart, the vaccinations levels fell due to no health coverage, poor economics and a fear of vaccines perpetuated by anti vaccination proponent.

Part of the problem was

“changes in the immunization schedule during this period encouraged less intensive vaccination of children. Use of an alternative schedule of fewer doses of lower antigenic content (adult formulation) vaccine was allowed beginning in 1980.”

Good thing that doesn’t describe anyone in this country.  Who would be nuts enough to think that we give too may vaccines too soon?  Certainly no MD. That’s a path down which lies huge epidemics with horrific morbidity and mortality.

The old USSR  went from 3,000 diphtheria cases to 50,000 cases in 5 years  as vaccination rates fell from almost  universal coverage to 69% (7).  Diphtheria was not controlled until vaccination rates were pushed back into the low 90’s using the old schedule.

Vaccination rates are drifting down in some parts of the US. The bacteria and viruses are not gone and never will be.  As the vaccination rates fall, the herd loses its immunity and can no longer provide protection.  The risk is slowly building and there will be more outbreaks.  The reason to get vaccinated becomes increasingly compelling.  And only Jenny McCarthy will be satisfied if the epidemics return (6).
———
References

1) FEMS Microbiol Rev. 2007 Jan;31(1):52-63.C  Lessons from meningococcal carriage studies.    PMID: 17233635

2) J Infect Dis. 2008 Mar 1;197(5):737-43    Impact of meningococcal serogroup C conjugate vaccines on carriage and herd immunity.  PMID: 18271745
3) Clin Infect Dis. 2009 Jan 1;48(1):57-64.    Epidemiology of invasive pneumococcal disease among adult patients in barcelona before and after pediatric 7-valent pneumococcal conjugate vaccine introduction, 1997-2007.   PMID: 19035779

4) Effect of pneumococcal conjugate vaccine on pneumococcal meningitis. N Engl J Med. 2009 Jan 15;360(3):244-56. PMID: 19144940

5) http://www.metrokc.gov/health/immunization/compare.htm

6) http://www.time.com/time/health/article/0,8599,1888718,00.html

7) http://www.cdc.gov/ncidod/eid/vol4no4/vitek.htm

8) Pediatr Infect Dis J. 1987 Apr;6(4):364-71.   Pertussis in Sweden after the cessation of general immunization in 1979.

9) http://www.annals.org/cgi/content/full/128/1/64

10) http://www.metrokc.gov/health/immunization/compare.htm

11) http://jama.ama-assn.org/cgi/content/abstract/267/20/2745

12) http://www.cdc.gov/mmwr/preview/mmwrhtml/00046738.htm

13)  Glanz J, et al “Parental refusal of pertussis vaccination is associated with an increased risk of pertussis infection in children” Pediatrics 2009; DOI: 10.1542/peds.2008-2150.

14)  http://www.cdc.gov/ncidod/eid/vol4no4/vitek.htm

15) Only sex is as efficient a way to spread infection.  If someone coughs on you during sex, it’s all she wrote.  Make sure your affairs are in order.

Posted in: Public Health, Science and Medicine, Vaccines

Leave a Comment (43) ↓

43 thoughts on “Herd Immunity

  1. Jules says:

    But not to worry! If we all live healthfully and encourage the natural bacteria to grow on us that’ll keep all the bad bacterial away and our immune systems will be stronger!

    /snark

  2. Karl Withakay says:

    Obviously Mark knows this, (and I assume he didn’t mention it because the focus of the post is heard immunity and not disease eradication) but I just wanted to add that another key factor in the ability to eradicate smallpox was that there was no animal reservoir for it to hide in.

    Zoonotic diseases are far more difficult to eradicate due to the difficulty in vaccinating or otherwise eliminating the disease from an entire population of one or more (non-domesticated) animal species.

  3. trrll says:

    Should adults be getting pertussis boosters?

  4. daedalus2u says:

    I believe that adults are given pertussis boosters. I think I got a DPT at my last physical.

    http://www.cdc.gov/vaccines/recs/schedules/default.htm#adult

    I can’t keep track of such things, that is what I rely on my health care professionals to do.

  5. TsuDhoNimh says:

    trrl –
    Yes … if only to keep us from spreading it to children.

    although a 4-week cough sounds yucky too.

  6. hatch_xanadu says:

    Thanks for this. Anybody else having trouble with the YouTube link, though?

  7. hatch_xanadu says:

    And heh — your #8 reference made the sunglasses smiley. :)

  8. beatis says:

    “Anybody else having trouble with the YouTube link, though?”

    Yes

  9. wales says:

    One question about herd immunity with regard to Pertussis. Dr. Crislip states “Immunity rates needed to protect the population from pertussis are about 94%, while virus spread is decreased if immunity rates are only 80% or so”. What is the current population-wide vaccine coverage rate for pertussis? Even if one assumes that 100% of children from age 0-18 are vaccinated, that is nowhere near 80 or 90% of the entire US population. How many adults are getting boosters? Does anyone have statistics on this? It would seem that the overall population coverage rates must already be (and have been for quite some time) MUCH lower than 80% due to waning immunity.

  10. wales says:

    I have a few more questions regarding the pertussis comments. Pardon my nitpicking, but I do like to check facts.

    1) Could you please provide a good link to your footnote 11? It responds with page requested not found.

    I would like to read more about that figure of 95% pertussis vaccine efficacy, as both Infanrix and DAPTACEL vaccine pkg inserts show efficacy rates of only about 85% for the pertussis component (using the WHO case definition of 21 consecutive days of paroxysmal cough with culture or serologic confirmation or epidemiologic link to a confirmed case). Not sure how the WHO definition compares with your definition of “severe clinical illness”. Perhaps you could elaborate upon the different definitions as I cannot find any other references regarding the vaccine efficacy against severe clinical illness.

    http://us.gsk.com/products/assets/us_infanrix.pdf

    https://www.vaccineshoppe.com/index.cfm?fa=anon.piexpress

    95% efficacy also conflicts with this article from the Atlanta Journal Constitution about recent outbreaks of pertussis involving fully vaccinated individuals which quotes Walter Orenstein (formerly with the CDC, now with the Gates Fdn) as stating that the pertussis vaccine is only 85% effective.

    http://www.ajc.com/health/content/metro/stories/2009/03/22/whooping_cough_vaccine.html

    2) Dr. Crislip states “Pertussis cases have been climbing. There were, in 2007, 10,000 cases of pertussis in the US, a new record.” A new record since when? The CDC’s Pink Book chapter on Pertussis states “Pertussis incidence has been gradually increasing since the early 1980s. A total of 25,827 cases was reported in 2004, the largest number since 1959. The reasons for the increase are not clear.” Early 80’s, I don’t think Jenny McCarthy had even given birth yet.

    3) In the US “the rate of pertussis peaked in the 1930s, with 265,269 cases and 7518 deaths reported in the United States.” And “Before the vaccine pertussis killed about 8000 children a year”

    Questions: 7,518 deaths in the 1930’s, is that for a particular year?

    I couldn’t find Pertussis mortality statistics in the Seattle and King County public health site cited in footnote 10 regarding 8,000 child deaths annually prior to vaccine development. According to US Vital Statistics data, you have look back to pre-1930 for TOTAL death rates (not just children) that exceed 6,000 annually. Since the 8,000 child deaths exceeds the 1930 total deaths figure, it must be referring to an even earlier period, perhaps 1920?

    1930 – 5,904 total deaths
    1940 – 2,904 total deaths

    (Pertussis mortality data source: US Bureau of the Census, Historical Statistics of the United States, Colonial Times to 1970 (Part 1)

    According to the Pink Book, Pertussis vaccine was not widely used until the mid 1940’s.

    When disease mortality statistics are vaguely cited as “before the vaccine” in support of vaccine efficacy it is misleading (and a good example of cherry-picking) if not specified how LONG before the vaccine. 20-25 years? It makes a difference when mortality rates were continually declining during those 20-25 years prior to the vaccine’s development and widespread use. For the sake of coherency “before the vaccine” should mean IMMEDIATELY before the vaccine. A more accurate statement would be “before the vaccine, circa 1940 the total mortality rate for pertussis was about 3,000 annually”. Of course, 8,000 children dying sounds more frightening than 3,000 citizens dying.

  11. wales says:

    I must be blind because I cannot find the information cited in your footnote 9 in the James Cherry editorial article. It is possible there is a different source not cited here?

  12. Th1Th2 says:

    Herd immunity is simply a community of vaccinated people with abnormal and damaged immune system.

  13. wales says:

    Thanks again for the footnotes. I always learn something by reading the source material.

    Footnote 7 cites a paper about Diphthera resurgence which says “Arguably the most important factor for the diphtheria epidemic was the development of large populations of adults susceptible to the disease as a consequence of successful childhood vaccination programs. The decreased opportunity for naturally acquired immunity, along with the waning of vaccine-induced immunity in the absence of routine adult revaccination, has resulted in a high proportion of adults susceptible to diphtheria as documented by serologic studies in many countries.”

    As discussed elsewhere on this site, vaccine induce herd immunity can be a double-edged sword for diseases like Measles and Diphtheria, where naturally acquired immunity is replaced by vaccine induced immunity resulting in new groups of higher-risk susceptibles (infants and adults) due to waning immunity. I suspect this may also be one of the causes of Pertussis increase, though the CDC’s Pink Book statement regarding the increase of pertussis in the US since the early 1980’s is “The reasons for the increase are not clear”. And of course the media will attribute outbreaks entirely to vaccine refusers, ignoring the effect of the temporary nature of most vaccine induced herd immunity. In fact when the Measles vaccine campaign began in the 1960′s it was touted as a permanent lifelong measles preventative. The parents of those who were involuntarily signed up as infants and children for vaccine induced immunity didn’t realize that lifelong boosters were required to maintain it. Few people even realize this today (witness the comments here about DPT boosters for adults).

    Statements made by many on this site that herd immunity is safe and effective ignore this consequence of vaccine induced herd immunity (probably because they think it can be easily solved by yet more boosters). Good luck getting a population of 300 million to submit to lifelong boosters.

    Footnote 12 is VERY interesting, though a bit outdated. “Update: Vaccine Side Effects, Adverse Reactions, Contraindications, and Precautions Recommendations of the Advisory Committee on Immunization Practices (ACIP)” Though I cannot locate it in your post except as a footnote.

    Dr. Crislip, thanks for a very interesting post. I look forward to your comments. I know you are very busy, but I am very patient.

  14. overshoot says:

    As discussed elsewhere on this site, vaccine induce herd immunity can be a double-edged sword for diseases like Measles and Diphtheria, where naturally acquired immunity is replaced by vaccine induced immunity resulting in new groups of higher-risk susceptibles (infants and adults) due to waning immunity.

    The alternative is to keep the disease circulating in the population. We know the consequences of that — and in the end, your worst-case scenario for vaccination is still less than having it become endemic.

    People are either:
    1) Susceptible,
    2) Immune due to vaccination, or
    3) Immune due to the disease

    The only one that doesn’t ultimately involve morbidity and mortality from the disease is immunization. What body count do you consider acceptable?

    Statements made by many on this site that herd immunity is safe and effective ignore this consequence of vaccine induced herd immunity (probably because they think it can be easily solved by yet more boosters). Good luck getting a population of 300 million to submit to lifelong boosters.

    Funny you should mention that — the DT booster uptake is actually quite good.

  15. Mark Crislip says:

    argh.

    screwed by lazyness (cut and pasted from prior writing) and auto numbering.

    I’ll fix the footnotes this weekend

  16. Calli Arcale says:

    wales:

    2) Dr. Crislip states “Pertussis cases have been climbing. There were, in 2007, 10,000 cases of pertussis in the US, a new record.” A new record since when? The CDC’s Pink Book chapter on Pertussis states “Pertussis incidence has been gradually increasing since the early 1980s. A total of 25,827 cases was reported in 2004, the largest number since 1959. The reasons for the increase are not clear.” Early 80’s, I don’t think Jenny McCarthy had even given birth yet.

    I wonder if it has anything to do with the fact that there were widespread concerns in the 1980s about the pertussis vaccine, specifically, because it was a whole-cell vaccine. Today, we mostly get acellular pertussis vaccines (the little “a” in DTaP is for “acelluar”), so the worry that was causing so many people to shy away from the pertussis vaccine in the 80s is no longer an issue.

    From Wikipedia on “DTP vaccine”:

    Severe problems closely following DPT immunization happen very rarely. These include a serious allergic reaction, prolonged seizures, a decrease in consciousness, lasting brain disease, or even death. British research in the 1980s into whole-cell DTP,[1] which is now rarely available in developed countries, suggested that such severe neurologic events occur after approximately 1 in 140,000 doses of the DPT vaccine (0.0007%). Most of the reactions to whole-cell DPT injection are thought to be from the pertussis component.

    I remember reading somewhere that there was a whole antivax movement revolving around pertussis because of this. So while Jenny McCarthy wasn’t involved, vaccine refusal was still probably a big factor. After all, vaccine refusal did not start with her — indeed, vaccine refusal movements have been around as long as vaccines. This particular one had more merit than the anti-Thimerosal and anti-MMR movements, but it still probably had something to do with the rise in pertussis cases in the 1980s.

  17. weing says:

    “Herd immunity is simply a community of vaccinated people with abnormal and damaged immune system.”

    Only half right, it’s vaccinated people plus people who have had the illness and all with normal immune systems.

  18. overshoot says:

    I remember reading somewhere that there was a whole antivax movement revolving around pertussis because of this.

    Brian Deer comes to the rescue again. It seems that the science behind the DPT scare isn’t all that solid either.

  19. Eric Jackson says:

    It’s actually quite disturbing how similar the 1970s DPT-brain damage scare and the present Wakefield MMR-Autism scare are. Though I don’t believe Wilson was handed a check by a legal firm to do so – he just took a mediocre study and threw it to the media.

  20. daedalus2u says:

    There is a good review paper on vaccines, what the historic sickness and death rates were and what they are now.

    http://jama.ama-assn.org/cgi/content/full/298/18/2155

    They do cite the sources for the data.

  21. wales says:

    Calli, my point was that despite the CDC saying there has been a steady increase since the 1980′s, there was a 60% decrease between 2004 and 2007.

  22. wales says:

    I apologize for another lengthy comment, but herd immunity is much more complex than it seems. Overshoot, I’m not sure that your assumption that the negative consequences of vaccine induced herd immunity are outweighed by the benefits is accurate. It may seem that way at this exact point in time, but a verdict has not been reached on the long term impact of these epidemiological shifts caused by vaccine induced herd immunity.

    In the Vaccines textbook by Plotkin, Orenstein & Offit (2008), the Community Immunity chapter by Paul Fine is very informative about herd immunity.

    Fine says this about Pertussis herd immunity “Pertussis is thus another example of an infection for which the immunity profile has changed greatly in recent decades in many populations: from a predominance of immunity attributable only to natural infection and boosted by frequent reexposure (now restricted to older individuals), to immunity attributable largely to killed whole-cell vaccines which waned as natural exposure became less frequent (in a high proportion of individuals born since 1950), and now to immunity attributable largely to various acellular vaccines (in younger individuals). Each of these forms of immunity is likely to have different implications for protection against infection, disease and infectiousness. The long-term implications of these changes are as yet unclear. “

    “In addition, there is evidence that pertussis vaccines provide greater protection against pertussis disease than they do against infection with B. Pertussis, and that adults contribute to transmission of the infection with or without manifesting characteristic signs of the disease.” Let’s remember that, instead of scapegoating “anti-vax” parents for not vaccinating their kids. Scapegoating usually is an oversimplification of a more complex issue. It is likely that the parents with waning vaccine induced immunity are the major problem rather than unvaccinated children, with US kindergarten vaccination coverage at 95%.

    The Fine chapter outlines similar circumstances for other diseases. Britain experienced a major “post honeymoon” epidemic of Mumps in 2004-2006 with more than 40,000 cases in 2005. A post honeymoon epidemic is due to epidemiological shifts caused by vaccine induced herd immunity. It occurs as the naturally immune part of the population decreases and the vaccine-induced immune part of the population grows, while the earlier vaccinees experience waning immunity, resulting in new groups of higher risk susceptibles (infants and children). This has been discussed elsewhere on this site with regard to Measles.

    The assumption that the benefits of vaccine induced immunity outweigh the negatives is based mostly on our experience in the post-vaccine honeymoon periods for these diseases. It will be easy to blame vaccine refusers for future epidemics, but those who understand the complexity of the problem should be honest when educating the rest of the public about herd immunity.

  23. weing says:

    You keep repeating the same nonsense. What is the source of the mumps? That’s what it’s caused by in the setting of waning immunity. If you had no more virus around, you would not have an outbreak.

  24. wales says:

    You are entitled to your opinion Weing. Not all diseases are eradicable. Viral Infections of Humans by A. Evans & R. Kaslow categorizes Mumps and Rubella as “potentially eradicable”, Measles as “not now eradicable”. They discuss various obstacles to eradication, but vaccine refusal is not one of them.

  25. weing says:

    Actually, they do mention it on page 45. The problem of vaccine refusal wasn’t as significant when that book was written. They also mention waning immunity from naturally occurring infection as a problem in the third world. I concern myself with how to make the diseases eradicable. Vaccine refusal is just another factor making eradication more difficult.

  26. wales says:

    I couldn’t find that reference on page 45, unless you’re referring to “language, ethnic and socioeconomic barriers”.

    There are different degrees of disease control: control, elimination, eradication. So far eradication has proven very elusive. I wonder if all the resources put toward that particular goal would be better used elsewhere. If eradication requires draconian laws for society, fear campaigns and social norming, I question whether or not eradication is more beneficial than elimination or control.

  27. weing says:

    14.1.2 Eradication versus Control in the 4th edition. Anyway, what’s the difference between eradication and elimination? And I find that control requires the draconian laws, fear campaigns, and social normings that you want to avoid.

  28. wales says:

    If you don’t know the difference between the epidemiological definitions of elimination and eradication you need to do some more reading.

    Here’s an informative chapter on control and eradication from a book called Disease Control Priorities in Developing Countries. Even reading the conclusion is enlightening. Small pox has been the only successful eradication because it was uniquely suited to eradication for various reasons.

    http://files.dcp2.org/pdf/DCP/DCP62.pdf

  29. weing says:

    In the global village that we have become, it appears to be a distinction without a difference, eradication is global and elimination is local. Strictly speaking, when I last checked, smallpox had not yet been eradicated. The potential for terrorists to get their hands on the virus and disseminating it again still exists.

  30. overshoot says:

    The potential for terrorists to get their hands on the virus and disseminating it again still exists.

    They wouldn’t have to do any high-security breakins — the sequence is out there, so all they’d need to do is synthesize it.

  31. The Blind Watchmaker says:

    “Eric ‘Stumpy Joe’ Childs”….love the Spinal Tap reference.

    And yes, in answer to Trrl’s question above. Adults are being boostered against pertussis now (at least they should be).

    Adults under the age of 65 should have the TdaP vaccine instead of the Td for their next tetanus shot (Tetanus/diptheria boosters are every 10 years for adults, or shortly after a bad cut if the last one was over 5 years ago). This is given once. In fact, if it has been over 2 years since the last Td, you are eligible for the TdaP at the next routine check up. For now, this is a one time booster. Then the Td resumes every 10 years.

  32. pmoran says:

    Overshoot “They wouldn’t have to do any high-security breakins — the sequence is out there, so all they’d need to do is synthesize it.”

    Smallpox is a relatively large and complex virus. Is this yet possible?

  33. overshoot says:

    Smallpox is a relatively large and complex virus. Is this yet possible?

    I hope not. Key word: “yet.”

  34. Diane says:

    MC, while you are fixing the footnotes, would you fix the youtube link as well, please?
    The page I get says that a bad video is embedded. I think in this case “bad” means “won’t play”.

    Thanks,
    Diane

  35. bcorden says:

    “Twelve percent to 32% of persons with prolonged cough have been found to have pertussis.”

    It is interesting that a recent article in the British Medical Journal on chronic cough in adults doesn’t appear to mention pertussis. And this in the a country with a presumed high prevalance rate of pertussis carriage:

    “In primary care the cause of chronic cough is often uncertain, and asthma is a common diagnosis. In a study in secondary care of 78 adult non-smokers with chronic cough and a normal chest x ray, in 73 (94%) the cough was considered to be caused by one or more of the “pathogenic triad” of asthma, gastro-oesophageal reflux, and postnasal drip syndrome. In 48 patients (62%) there was more than one cause.3 Studies from specialist cough clinics found that the cause of chronic cough can be established in 89-100% of cases, making the previously popular diagnosis of “psychogenic cough” redundant. In smokers, chronic cough is common and can also be the presenting feature of chronic obstructive pulmonary disease or bronchogenic carcinoma. “

  36. teeps29 says:

    The Youtube link doesn’t work. Remove the period at the end of the sentence from the link and it will work. In the meantime, you can copy the URL up to and not including the period, then paste it into a browser window, to view the video

  37. Psyche78 says:

    [quote]And yes, in answer to Trrl’s question above. Adults are being boostered against pertussis now (at least they should be).[/quote] According to the CDC, a survey in 2007 found that only 2% of adults 18-64 were up-to-date on TdaP vaccinations. http://www.nfid.org/pdf/publications/adultimmcta.pdf

    Correct me if I am wrong, but that is likely to be less than then necessary percentage of population in order to have herd immunity.

    And for the record, the DT booster rate (as found by the same study) is only 57% in adults.

  38. wales says:

    According to the US Census Bureau, approximately 25% of the US population is comprised of individuals 18 and younger and about 15% is comprised of those 65 and older (presumably with natural immunity to pertussis). If it’s true that only 2% of adults are up to date on pertussis vaccination, then US herd immunity is currently considerably less than 50%.

    Perhaps we’ve been unknowingly experiencing an epidemic(s) without being aware of it, especially as adults are often asymptomatic carriers. It will be interesting to see what happens as the “cushion” of naturally immune individuals eventually dissipates.

  39. wales says:

    The reference cited by psyche78 does indeed state that only 2% of adults are up to date on DTaP, but that 57% of adults have had a DT booster in the past ten years. Why are physicians giving DT instead of DTaP to adults? Are adults at higher risk for adverse reactions to the pertussis component?

    Also, the adult DTaP package insert says the efficacy rates for adults were inferred from the DTaP efficacy rates for children. Some other vaccines are less effective in older adults (such as influenza), how do we know that the DTaP efficacy is as high as 85% for adults sans actual efficacy studies?

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