It’s hard to believe that it’s been 2 years since Iowa’s 2006 mumps outbreak (more background and details on that here, here, here, and here).

By the time the outbreak ended, 8 states had been heavily affected (and 45 reported at least one case), with a total of 6584 cases of mumps and 85 hospitalizations reported by the end of 2006. All told, this was the largest outbreak of the virus in approximately 20 years, after a 1986-1990 outbreak resulted in a change in the recommended vaccine schedule (adding a booster shot of MMR).

A paper out in today’s New England Journal analyzes the outbreak–what happened and why, and what public health professionals can do to prevent future such outbreaks. More after the jump.

The NEJM paper examined cases of mumps dating back to 2000 and continuing up to mid-2007 in order to determine variation in the virus and case populations (including vaccination status) pre- and post-resurgence. The central question is, why did a mumps outbreak occur in this population? Most of the individuals affected had received 2 doses of the MMR vaccine, the first in childhood and the second in adolescence. Theoretically, most of them should be protected against the virus–so why the outbreak?

The authors examined several possibilities, and didn’t conclusively rule out any of them. First, were records and reports of vaccine doses accurate? Could some of the cases have received the measles-only vaccine, rather than the MMR combination? The sheer numbers of each of those vaccines administered suggests that was an unlikely explanation.

Was the outbreak possible because the hardest-hit group–college students age 18-24–had little or no exposure previously to wild mumps virus, therefore not boosting their immunity? We already know that the mumps vaccine isn’t as good as the measles or rubella vaccines it’s given along with, so even with 2 vaccinations, there would be a small percentage of individuals who would lack immunity to the virus (as I explained here). In those in whom the vaccine “took,” does immunity start to wane in a fairly short time period, making them again vulnerable to infection? This could certainly play a role in an outbreak, and the authors note that “if population immunity is already near the herd threshold, even negligible waning immunity, particularly when combined with increased exposure, could potentiate an outbreak.”

A second explanation, and not necessarily mutually exclusive, would be that the strain of virus–serotype G–wasn’t a close enough match to the vaccine strain (genotype A)
to provide good cross-protection. However, outbreaks of the same strain in Europe responded to increased vaccination with the genotype A strain, suggesting that the vaccine does provide adequate protection. This is good news considering that, because a large population of the world doesn’t vaccinate against mumps, imported cases are likely to continue.

Finally, with lines like “CDC: Waning immunity blamed for outbreak of 6,600 cases”, I expect the anti-vaccine groups to be once again railing against the mumps vaccine, and ignoring the fact that prior to vaccine introduction, there were 152,209 cases of mumps a year–a rate that had dropped 98% by 1985. Still, the possibility of waning immunity coupled with more people avoiding the MMR shot for their children and a regular stream of imported cases means that outbreaks like this may become more common–and vaccination policy again my change.

Dayan, G.H. (2008). Recent Resurgence of Mumps in the United States. New England Journal of Medicine, 358 (15), 1580-1589. Link.

Image from http://www.mullhaven.co.uk/mumps.jpg

Comments

  1. #1 jspreen
    April 10, 2008

    In those in whom the vaccine “took,” does immunity start to wane in a fairly short time period, making them again vulnerable to infection?

    Why, yes, of course, didn’t you know?? I figured that out ages ago and methinks all vaccines should hop over to the flu-vaccine method: A shot each and every year.

    Ha Ha Ha Ha HAHAHAHAAAAAAAAAAAAAAAAAAAAAAAAAHAHA.

    Sorry. It’s stronger than me, it really is. Each and every time I read some good ol’ vaccination groupie’s post, my fingers become itchy and I must Type and Post. Sorry.

  2. #2 John Marley
    April 10, 2008

    jspreen:

    you don’t ever actually read the posts or comments, do you?

  3. #3 Nat
    April 10, 2008

    Nice post. Me Likee.

    Thanks for writing it.

    (awaiting inundation by ravenous hordes of luddites)

  4. #4 Dr. Free-Ride
    April 11, 2008

    Nat, we Luddites are against *stupid* technology. Vaccines are smart technology. Don’t hate on the Luddites.

  5. #5 Nat
    April 11, 2008

    One erudite Assistant Professor a horde does not make.

    I used Luddite to indicate a dislike of 19th century technology. I’ll help you break a wooden loom if only I could find one somewhere… damn post industrial society.

  6. #6 Dave
    April 11, 2008

    I seem to recall that, at the time of the outbreak, lab tests for mumps on at least some of the victims were showing negative, thus leading to speculation that maybe it wasn’t mumps at all, but parainfluenza or some such. Was this ever resolved?

  7. #7 Trisha
    April 11, 2008

    vaccination groupie? Oh, well, maybe that is what I am too. Not such a bad thing.

  8. #8 regülatör
    April 12, 2008

    that is what I am too. Not such a bad

  9. #9 Patrick B
    April 12, 2008

    I’m a total vaccination groupie. But then I also like washing my hands, pasteurizing my milk, and using flush toilets. Call me crazy.

  10. #10 Truthbendsover
    April 13, 2008

    “I’m a total vaccination groupie.” Pulease, there is a world of a difference in keeping something clean – like the water and food supply, and injecting foreign proteins, CCL – i.e. cancer cells, synthetic DNA and RNA, bits of monkey kidneys and heavy metals directly into the bloodstreams of innocent newborns with underdeveloped immune systems. What is this groupie thing anyway – oh yes, the hysterical, emotionally driven need to identify with the rest of the sheep. Give yourself a Darwin Award.

  11. #11 ElkMountainMan
    April 13, 2008

    Truthbendsover, the MMR vaccine is administered at 12 to 15 months of age and again in adolescence. You would know this if you had read Tara’s post or her links. Or perhaps I’m being insensitive to a national difference: are adolescents and 12- to 15-month-old babies still considered “newborns” where you live?

    A mumps vaccine was licensed in the USA in 1967. Most states had made it (and its more effective successors) mandatory for school entrance by 1985.

    What, in your opinion, caused the 98% reduction in mumps in less than 20 years in the United States? Was it a remarkable advance in clean water? In milk pasteurization? In availability of flush toilets? Or didn’t it happen at all, since someone remarkably similar to you claims here that science has contributed nothing to health advances?

    “Bends,” you and your cyber-friends have every right in the world to spend your time designing clever insults involving memes, sheep, and shit with the primary goal and outcome of amusing yourselves. Most doctors will take no notice of you as they spend their time designing new and better vaccines to help others.

  12. #12 Chrissl
    April 13, 2008

    I’m old enough to remember when everyone expected to get measles, mumps and chicken pox at some point during their childhood or adolescence. (I didn’t get mumps till I was in junior high: talk about misery!)

    I think that for many years we greatly under-estimated just how serious these diseases were, just because they were so common and everybody had them. Now that everyone *doesn’t* get them any more, it’s slowly dawning on us that all three of these, and especially measles, are really quite serious diseases with considerable risks attached.

    I think this makes some aspects of the history of medicine a bit more understandable — perhaps part of why immunization took so long to become accepted practice in the first place is because it was hard for people to realize just how devastating seemingly “normal” illnesses really were. And also why the first epidemics of European diseases were so devastating to native Americans.

  13. #13 Clinton
    April 24, 2008

    I beg to differ Chrissl, I think that now that these diseases are becoming uncommon, people are FORGETTING how serious some of these diseases are. I agree with your point though.

    The main argument by “anti-vax groupies” is that the side effects are WORSE than the diseases they prevent. I’ve had people tell me point blank that they’d rather let their kid get whooping cough (the nastiest cough ever that leaves you continually breathless and even makes you vomit) rather than suffer the minuscule risk of encephalopathy. Granted, her child did have a seizure disorder from some unknown source, which she associated with the older DTP vaccine (why it was given instead of the DTaP vaccine is a mystery to me.)

    Regardless, this sort of skewed cost:benefit analysis that RELIES on the herd immunity they are purposefully opting out of is a sad example of what it means to forget.

  14. #14 MyFrom
    May 5, 2008

    that is what I am too thanks

  15. #15 Zayıflama
    June 13, 2008

    Kidney stone disease affects approximately 5% of Americans. While several risk factors are well-established, including genetic predisposition, metabolic diseases, lifestyle, and diet, there are still questions over the actual mechanism of calcium stone formation. Many cases do not have any kind of underlying disorder and therefore it is difficult to know how to treat these patients to prevent further stone formation.

  16. #16 ADSL Başvuru
    June 13, 2008

    Sorry. It’s stronger than me, it really is. Each and every time I read some good ol’ vaccination groupie’s post, my fingers become itchy and I must Type and Post. Sorry.

  17. #17 Diyet
    June 13, 2008

    A second explanation, and not necessarily mutually exclusive, would be that the strain of virus–serotype G–wasn’t a close enough match to the vaccine strain (genotype A)
    to provide good cross-protection. However, outbreaks of the same strain in Europe responded to increased vaccination with the genotype A strain, suggesting that the vaccine does provide adequate protection. This is good news considering that, because a large population of the world doesn’t vaccinate against mumps, imported cases are likely to continue.