Here we go again, another anti-vaccine trope based on one paper without adequate scientific criticism of said paper. What is this trope? Mumps and measles infections prevent heart disease and stroke. Let me jump right to the conclusion – wrong.
Although I’ve seen this story before, like most zombie tropes in the anti-vaccine world, this one has come back from the dead. In the pseudoscientific website, Health Impact News, the author writes:
By my calculations, natural infection with the measles and mumps will prevent millions of heart attacks and strokes. Why is this information not all over the TV and internet? I will tell you why. Because mainstream media is in bed with Big Pharma who pay their bills. The politicians are slaves to their corporate masters. Our children should be exposed to every virus and bacteria for which a vaccine exists.
The author’s shrill claim is based on a 2015 article published in the lower impact factor journal, Atherosclerosis. The authors concluded that “measles and mumps, especially in case of both infections, were associated with lower risks of mortality from atherosclerotic CVD (cardiovascular disease).”
Now, it’s time to turn a critical and skeptical eye towards that article.
Mumps and measles infections prevent heart disease – the paper
The study evaluated lifestyle questionnaires from 43,689 men and 60,147 women who were aged 40-79 years at the baseline period of 1988-1990. Individuals of that age probably were not vaccinated against measles or mumps, since that vaccine wasn’t available for children until the late 1960s, when the individuals in the study would have been 20-50 years old. The questionnaire included history of measles and mumps, and were followed until 2009.
The authors then determined hazard ratios (HR, see Note 1) for mortality from cardiovascular disease (CVD) between groups with history of measles and/or mumps infection versus those who did not have those infections. Here are some of the results of the analysis:
- Men with history of measles had an HR for all CVD deaths of 0.92.
- Men with history of both measles and mumps had an HR for CVD deaths of 0.80.
- Women with both infections had an HR for all CVD deaths of 0.85.
The researchers also looked at comparisons between infected and non-infected groups for various types of CVD, but these data probably are the most important.
The study also attempted to show that there was no difference in infected and non-infected groups for a series of confounding variables. They include:
- Body mass index
- Previous history of CVD
- Exercise level
- Stress level
Taken at face value, the research does seem to support the contention that we shouldn’t get the MMR vaccine to protect ourselves against measles and mumps, because catching those diseases may protect us against cardiovascular disease when we get older. But really, does it really gives us evidence to quit vaccinating? Let’s take look.
- This is a one-off primary study that has not been confirmed by any other researchers. This places it at the lower end of the hierarchy of scientific research.
- The authors did not propose a biologically plausible explanation. If one is to propose a correlation between two events, especially when the temporal difference is over 50-70 years, one must also propose a plausible reason why you might assume there is correlation. Is there a plausible reason for anyone to believe that a mumps or measles infection will protect someone from cardiovascular disease? I have a scientific bias towards plausibility, otherwise we can propose inane scientific hypotheses that waste the time of everyone involved.
- There is simply little evidence that measles or mumps is correlated with CVD – a review of PubMed for any articles that might establish a relationship between mumps and/or measles with CVD provided me with two articles. The first is the one we are discussing herein. The second, also published in Atherosclerosis, seems to indicate that mumps and measles is related to higher rates of CVD. This is why cherry picking is bad – you seek out articles that support your pre-conceived conclusion rather than let all of the evidence lead you to a conclusion.
- The use of questionnaires for epidemiological studies is frowned upon by many researchers. The reasons for this are many, but they include a reliance upon the memory of the participant for events that may be 50 or 60 years in the past. For a highly infectious disease like measles, it’s hard to believe that 50% of the participants in this survey caught neither mumps or measles as a child. It’s more likely that they actually had caught the disease but forgotten about it. A properly designed study would have measured measles and mumps antibodies then determined the HR. Or used actual medical records (like a lot of vaccine studies use for case control studies of vaccine effectiveness and safety).
- The hazard ratios were tiny. Yes, it appears that mumps and measles infections prevent heart disease – the data seem to show a 8-20% reduction in CVD risk. But is that clinically significant? If being vaccinated against measles and mumps showed a 200-300% increase in the risk of CVD, I would be impressed and troubled by the results. But such a tiny reduction in the risk could be explained by anything. A missing confounder. Other infectious diseases. Nutritional levels. In fact, I can go on and on. Furthermore, is an 8% reduction in risk of CVD, if it is valid, worth the risk of death or disabling conditions from contracting measles or mumps? Although the question is rhetorical, it’s actually necessary to come to a conclusion based on the results provided.
- Speaking of vaccines, why wasn’t vaccine status asked (although the same memory issues that would plague this questionnaire would still bother me here)? Even though most of the participants probably would have missed the vaccine, some may have gotten it.
- The results also showed a 5-20% increase in risk of CVD for women who had either mumps or measles. That result alone throws into question the whole study, because the results are all over the place.
Can one use this article to claim that mumps and measles infections prevent heart disease and stroke? Not really. The best I can say, and I’m doing this with a lot of trepidation, is that this study provides us with observational data, not a confirmation or refutation of a hypothesis about mumps and measles infections. It certainly does not give us any reason whatsoever to change public health priorities in vaccinating against mumps and measles despite the anti-vaccine tropes.
- A hazard ratio describes a ratio of hazard rates between two events. In the case of this study, if the rate of cardiovascular disease mortality for the mumps infected group is 1.0 and it’s 2.0 for the non-infected group, then the hazard ratio is 0.5. That is the mumps infected group is only 50% as likely to have died of cardiovascular disease as the non-infected group.