I’m part of the generation who vividly remembers mumps’ high fever and the itching from chicken pox. These disease rates were not brought under control by improved public sanitation in the post-WWII era. They’re spread by close contact (and airborne droplets) in public places we can’t avoid (e.g. schools) and deaths were reduced by better fever control, access to health care and improved nutrition. But still, the risk of death from measles was cited at about 1/1000 and Rubella infection in pregnant women was found to be a potent teratogen. The Measles, Mumps and Rubella (MMR) vaccine was developed too late for me, but it became widely available in the early 70’s. Since that time it has prevented deaths, male sterility, malformations and retardation in children.

The numbers of children saved from infection risks is not particularly easy to calculate, as many websites list infection rates and adverse events differently. It’s important to compare current disease rates in developed countries with pre-vaccine rates. And before comparing numbers, fluctuation in birth rates and age-based disease susceptibility should be factored in. For instance, rates of measles jumped every time it “had a chance” before the vaccine was available, that is, rates peaked every time a new generation was born. After adjusting the rates, it’s easy to see the savings accumulate, impacting millions of children’s lives worldwide.

It’s also easy to see how the numbers can be misconstrued when they are not adjusted for demographics. Many people have claimed that infection rates actually went down before the vaccine came out–well, they did! But that was because the susceptible population declined in the early 60’s, the end of the baby-boomers. The measles peak rates were naturally cyclical, so a downturn just prior to vaccine release was not a reason to claim that the MMR vaccine didn’t work. Connecting two unrelated events is an example of what’s called a logical fallacy.

Websites listing reliable statistics include: US Census, Children’s Hospital of Philadelphia, CDC, World Health Organization and the FDA. These sites list statistically accurate rates of benefits, including the far smaller rates of risks, as well as the nature of the events. By far, the most common findings with modern vaccines are a sore infection site and a slight headache. Rarely a mild fever is found and more rarely still are reactions like neurologic disorders or allergic events. Part of the problem in evaluating and communicating vaccine risks and benefits is the shear absence of diseases today–it’s easy to forget the things that are no longer in our faces.

Measles is no longer found (“endemic”) in the US, but we can see the MMR benefits if we consider what would happen in a given year if the rates were unchecked by the vaccine. In the US today, take the figure of ~4M new babies born in a year (the figure from the 2010 US Census). Using prior measles infection/death rates (which peaked cyclically before the vaccine was out), we would see over 16,000 new cases/year in the US alone, with ~16 deaths. The annual adverse event rates, now known from millions of vaccinated children, would be estimated at ~40 SAEs. This is ~40 potential risks of vaccine-triggered adverse findings, to compare against the known risk to ~16,000 children from actually contracting the disease. And this is a conservative estimate of SAEs. In other words higher is more likely to be true, because when adverse events are reported for vaccines, individual doctors or parents can’t tell anything about causality–they only know and report an event that occurred in the short time after a vaccine was delivered. As a simple case, let’s use a fever occurring the day after a vaccine. It’s possible the child might have gotten a minor cold that day. But here is the way our adverse event reporting system works: if a parent tells their pediatrician their child got a fever post-MMR vaccination, the doctor must record it as potentially vaccine-related. But in no way does this type of report allow someone to scientifically “know” the cause of the event, so many other factors could have contributed.

A major problem with rare coincidences like these is that they commonly lead people to misattribute or wrongfully claim that something was caused because of something that preceded it. As another illustration, lightning could strike shortly before an earthquake. People in ancient cultures might explain this with myths like the gods’ anger. But today, we understand from physics that the friction energy building up into lightning is very different than the earth’s stresses building up into an earthquake. Despite advances in knowledge, human nature hasn’t changed. People naturally want to name a cause for a bad or scary event. They want to know how to avoid them in the future or warn others. And we feel especially threatened when diseases affect our children.
 

References

  1. Chigwedere P, Seage GR, Gruskin S, Lee TH, Essex M (October 2008). “Estimating the Lost Benefits of Antiretroviral Drug Use in South Africa”. Journal of acquired immune deficiency syndromes (1999) 49 (4): 410–415