14 August 2010
Mumps: Gone? Uh uh.
The mumps vaccine was introduced in the US in late 1967. In 1968 there were 185,691 cases reported. The incidence then fell precipitously, and fewer than 300 cases a year were reported in 2001-2003. The CDC was confident that mumps could be eliminated by 2010. But in 2006, the largest outbreak in 20 years occurred, starting in Iowa and mostly involving college students. By year’s end over 6,500 cases had been identified, of which 85 required hospitalization. It is likely that the virus arrived from Great Britain, where an identical strain had been circulating earlier. A study just reported (Kutty PK et al., J Infect Dis. 2010 Sept 1;202(5):667-74,) estimates the prevalence of adequate immunity in the college age population in the US at 90%. This sounds fine, but 90-92% immunity is required in our population to achieve the ‘herd immunity’ effect that prevents widespread communication of this highly infectious agent. And in some subpopulations the rate is even lower, setting us up for another outbreak. An accompanying editorial asks whether we all need a third dose of the combined measles, mumps, rubella vaccine, but the answer seems to be probably not. It is important to be vigilant; many parents think that mumps and other childhood diseases have been eradicated, but only about half of the world’s countries require immunization against mumps, and if you travel or receive foreign guests, you can be at risk.
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This seems similar to the measles outbreak that Tucson, AZ experiences a couple of years ago now...parents had stopped immunizing their children because the disease "seemed gone"...but then a visitor from Europe came over to visit a relative in the hospital...within weeks, there were 22 confirmed cases.
ReplyDeleteAubreyC595 should be interesting to follow outbreaks in the future, following the vaccine scare associated with autism. especially since some people believe the MMR vaccine has a direct correlation with autism.
ReplyDeleteIn regards to parents opting to not immunize their children, I found an article from a couple years ago that looked at the influence of media coverage of the MMR-autism controversy on vaccination rates: Pediatrics 2008; 121; e836-e843. They basically saw a decrease in vaccination rates when the MMR-autism study first came out, but the rates had gone back up to "baseline" by the time major media coverage was being done a couple years later. One of the speculations was that this was due to family physicians who had first come across the study and had passed the information down to their patients that resulted in the lower vaccination rates. This could explain how the general public had access to this information before the media presented the study.
ReplyDeleteIn theory, once we have been vaccinated and immunity is generated, memory T and B cells are established. In practice we may need boosters to retain immunity. Why?
ReplyDeleteWell, neither T cells nor B cells live forever; so as they gradually are replaced by "naive" cells, we will at some point lose effective immunity. At least that's the usual explanation. What the rate of decline is, is not well characterized, and it varies for the type of vaccine. I've read that about half of people who were vaccinated against smallpox (last in 1979, roughly) are still immune.
ReplyDeleteAs far as the MMR-Autism scare I personally would take the risk of vaccinating my children because if we do not reach herd immunity of 90-92% as the article states and even if we do reach herd immunity, there is always a chance that they might develop the measles, mumps, or rubella. Especially looking at when we are in college many of us live in dorms, with roommates, and are almost always in constant contact with other students we are at risk of developing an illness, whether the common cold or the measles. In college we have students from foreign countries who are here to earn an education that might not require vaccinations from the measles, mumps, or rubella (or in that fact many other diseases) that might be carriers of the diseases and if we come into contact with one of these students and are not vaccinated we might develop the disease. Another risk of not being vaccinated is when students study aboard and visit countries that might have a prevalence of diseases that they are not vaccinated from they might not be able to fight off an infection. The same was said during the Polio epidemic, people feared their children becoming vaccinated because there was a chance of their children developing Polio from the vaccination but the chance of coming down with Polio if they did not receive the vaccination was much greater.
ReplyDeleteFrom what I hear, disease control amongst international travel is extremely loose. Alot of times, I believe that they merely ask a person if they have some sort of rare disease before they embark in a new country. I think international regulations need to be maintained with some sort of system of documentation that relieves any paranoia about the spread of any "dying" diseases.
ReplyDeleteI feel that it is essential to continue to vaccinate the population against diseases such as measles, mumps, and rubella. As Dr. Cohen had stated above over time we do lose our immunity over time because our T and B cells do eventually get replaced by native cells leaving a significant amount of the population susceptible, especially those that have compromised immune systems. I was not too surprised with the numbers of sick individuals during the outbreak that occurred in 2006 considering the rising number of people that opt out of preventative measures such as being vaccinated. I myself was reluctant to get the chicken pox vaccine because I had never had chicken pox and I figured I wouldn’t be exposed to it. Going beyond this topic I think there is an interesting ethical issue here. The human species at this point in time has surpassed the survival of the fittest evolutionary constraint with the improvement of hygiene, better technology, and scientific leaps in preventative medicine however is this a good thing? By allowing weaker individuals to remain in the gene pool are we weakening our ability to fight disease as a whole. Was our adaptive immune system much more effective when we were exposed to a variety of different parasites, disease, and survival? Would it be beneficial to allow people to get sick?
ReplyDeleteWe never escape survival of the fittest, we are only exposed to novel environments. Don't forget that not everyone in the world has preventative (or any) medicine.
ReplyDeleteWell since the article refers to the United States my scope was focused on this country and life expectancy over the past 1000 years has nearly doubled and the population continues to grow. Therefore, more then just the fittest have been continuing into the next generation. As for the third world countries and regions not as fortunate as the westernized world it is possible that they have a better developed immune system because they have a higher level of exposure.
ReplyDeleteAubreyC595 @ Jason, my friend is leaving for India in 2 weeks all they require her to get is a malaria vaccine...loose indeed!
ReplyDeleteAubrey C595, there still isn't a malaria vaccine available. I guess what they really required her to have was malaria preventive pills, something like malarone. A vaccine would be wonderful, but the life cycle of the pathogen is so complex that no one has figured out how to do it. But she also should have had 2 hepatitis vaccines, yellow fever, typhoid, and updated her tetanus and polio...at least!
ReplyDeleteoops!mis type meant Hep's we were discussing malaria earlier so it was on the brain....still, loose!
ReplyDeleteBack in the 1970's and 1980's, it was very rare for a parent (in the U.S.) not to have their children immunized. They came from a generation that was all too familiar with the effects of polio, measles and mumps. Now, not only is there a greater distance in time from these once common childhood diseases, but we also are up against those who have been told of the risks associated with having their child vaccinated (thimerisal is a mercury-containing preservative used in some vaccines and is thought to increase the risk of autism). It is not surprising that the prevalence of adequate immunity in the college age population is only at 90%.
ReplyDelete@KellyG7630 - I think you bring up a great point. It is frustrating especially when high profile individuals like Jenny McCarthy promote antivaccination campaigns. It scares parents away from vaccinations (like MMR) ultimately putting their children at risk -- especially disease like measles are so contagious. Although we should be aware of vaccine associated risks, the benefits definitely outnumber the risks. I think one of the best examples of this is cited in a NEJM article. They discuss the polio vaccine that caused paralysis in 1/1 million doses or close contact, but as we know it helped to eradicate the disease (MacKay 2001). Paralysis is not something to shake a stick at, but risking polio, to me, is much worse.
ReplyDeleteMackay, Ian and Fred Rosen. Advances in Immunology. The New England Journal of Medicine 2001; 345:14.