White Coat Underground

Mumps redux

The resurgence of vaccine-preventable diseases is a fascinating, if unwanted, phenomenon. Pertussis, measles, and now mumps are cropping up after long periods of quiescence. Mumps has been generally very well-controlled since the adoption of wide-spread vaccination, with no nation-wide outbreaks, but there have been a number of regional outbreaks, most notably in 2006 and now again in 2009. Since the widespread use of two-dose vaccines, mumps cases in the US have dropped by more than 99%.

In an analysis of the 2006 outbreak the authors noted a three year periodicity to wide-spread mumps epidemics,and predicted a 2009 outbreak similar to the 2006 outbreak based on pre-outbreak epidemiology..  It appears they were right. The CDC is reporting a sudden outbreak among a religious community in the Northeast (they don’t say it explicitly but it appears to be an Orthodox Jewish community). The disease appears to have been imported from an ongoing UK outbreak, and then to have spread through the close quarters of a summer camp. As children returned home from camp, the disease spread through their communities.

The vaccination rate among those infected was significantly lower than the average for New York state, but still somewhat high (around 72% for those in whom vaccination status was known). This is below heard immunity rates, but obviously raises questions.

Mumps is not a benign disease. In the current outbreak, 9% of cases reported complications, including orchitis (inflammation of the testes sometimes leading to fertility problems) and deafness, which was in this case temporary. In the pre-vaccine era, about 10% of those infected developed meningitis, many became deaf, and many developed male fertility problems. 

This outbreak and the one in 2006 raise questions about the epidemiology of vaccine-era mumps and the optimal vaccine schedule.  What is not in question is the benefits of vaccination.  These outbreaks were not widespread, thanks largely to vaccination, sparing the population at large from the illness and its complications.  But it would be good to know how these outbreaks occur.  Do we need to consider a third dose of vaccine either generally or in certain communities? Do we need to limit contact with countries with high rates of disease?   

What is clear is the contrast between these outbreaks and the epidemics of mumps in the pre-vaccine era.  It is also clear that vaccination is imperfect, but still significantly better than allowing epidemic mumps. 

References

Barskey, A., Glasser, J., & LeBaron, C. (2009). Mumps resurgences in the United States: A historical perspective on unexpected elements☆ Vaccine, 27 (44), 6186-6195 DOI: 10.1016/j.vaccine.2009.06.109

“Mumps Outbreak — New York, New Jersey, Quebec, 2009.” MMWR: Morbidity and Mortality Weekly Report November 12, 2009 / 58(Dispatch);1-4.

Comments

  1. #1 Chuck
    November 13, 2009

    In your opinion,

    Is the number of cases in the vaccinated population due to vaccine failure, waning immunity, or differing strains becoming more prevalent?

  2. #2 PalMD
    November 13, 2009

    There’s no indication of a “strain” issue. Waning immunity may indeed be a problem, as there are fewer cases of wild-type mumps out there “re-immunizing” the immunized. “Vaccine failure” doesn’t appear to be a problem, as most people respond well.

  3. #3 Chuck
    November 13, 2009

    So it would be your opinion that a third booster of the existing mumps vaccine should take care of the problem in the future.

  4. #4 PalMD
    November 13, 2009

    The only way to know would be to study it. My opinion as to whether that would be the way to go is not too relevant.

  5. #5 Chuck
    November 13, 2009

    “Most of the cases were up to date on mumps vaccine: 63% of all cases and 84% of those 18-24 years old had received two vaccine doses. This suggests that vaccine failure likely contributed to the outbreak along with other factors such as waning immunity and high population density in the affected regions.”

    From the Washington State report that sparked my curiosity in my question.

    http://www.doh.wa.gov/EHSPHL/epitrends/09-epitrends/09-01-epitrends.pdf

  6. #6 PalMD
    November 13, 2009

    This depends on what one means by vaccine failure. Vaccination that leads to immunity is not a failure, but if that immunity wanes over time, this could be seen as “vax failure” (in quotes) or more precisely as waning immunity.

  7. #7 gaiainc
    November 13, 2009

    It would not surprise me that waning immunity is a problem and adults will need boosters once thought unnecessary. In 1999 I had to have titers done to prove I was immune to rubella before I could do my OB rotation. My titers were fine. Fast forward to 2008 and my prenatal titers were now equivocal. So I got the MMR again. I think that’s my fourth dose of MMR (I belonged in the cohort that needed to get reboosted around age 18 and it’s my fifth dose of measles since in 1999 my measles titer wasn’t up to snuff either), so I’m really hoping that I no longer need any more. That vaccine hurts.

    On the other hand, I take it as a good sign that vaccinations are out there, that they are working, and that I’m not seeing as much wild type to re-educate my immune system. If I have to get boosters as an adult, then I’m al for that.

  8. #8 PalMD
    November 13, 2009

    Forgot to give you the numbers: response rate for mumps vaccine, even after a single dose, is 95-99%.

    This implies that the failures were secondary vaccine failures rather than primary, which is interesting in that the approach to analysing and fixing the problem is different.

  9. #9 Chuck
    November 13, 2009

    That 95% may also be a little high as well

    “As has been mentioned, the given efficacy rate for the mumps vaccine is 95%. This is actually likely a bit high; previous outbreaks have suggested it’s more like 85-90% effective, so that as many as 15% of the vaccinated population won’t actually be immune.”

    http://scienceblogs.com/aetiology/2006/04/another_mumps_postisnt_the_vac.php

  10. #10 PalMD
    November 13, 2009

    Yes, I see you can read and that there are varying numbers, but do you have a point, because it isn’t clear. Stats show that whether you call it 85 or 95% effective, mumps rates dropped by >99% when regular vaccination became the rule.

  11. #11 Donna B.
    November 13, 2009

    #7 – that’s interesting to me, because I had to have MMR vaccinations either during my first trimester or right after birth every time I was pregnant. (I don’t remember which because the last pregnancy was 28 years ago!)

    I just remember the doctors telling my I showed no immunity. I should probably think about getting re-vaccinated for that, shouldn’t I? Especially now that I am around my pregnant daughter?

  12. #12 Chuck
    November 16, 2009

    “Stats show that whether you call it 85 or 95% effective, mumps rates dropped by >99% when regular vaccination became the rule.”

    The rule seems to be breaking if the rates are now increasing and primarily in the vaccinated population. What is causing this to happen?

    1) The vaccine does not elicit the proper immune response 15% of the time or a sub population (15%) of the vaccinated population cannot have a proper immune response.

    2) The initial immune response weakens over time for X% of the vaccinated population over Y number of years.

    3) The immune response originally created by the vaccine cannot protect the individuals from the current strains prevalent in the environment.

    So what should the proper response be?

    A) For #1 above, it is expected that occasional cases would happen over a period of time and no refinements or boosters will correct for this situation (The booster will also be ineffective 15% of the time or for 15% of the population) so no further action is necessary

    B) For #2 above, for the sake of simplicity and expediency in the medical community, the only variable will be in determining the correct number of years between vaccination using the existing vaccine formula

    C) For #3 above, reformulating the current mumps vaccine to adequately elicit the proper immune response and distribute the new vaccine to the population.

    Of the three choices, B requires the least amount of time and expenses (expenses also including negative PR that would happen in A and C)

    All three choices have different entities making gains or losses. Which one is best is dependent on what your perspective really is.

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