A: If you haven’t had one already, you should definitely get an MMR vaccine to prevent measles, mumps, and rubella! But no evidence so far supports the idea that your MMR vaccine might prevent COVID-19.
We’ve all seen the news: risk of dying of COVID-19 infection jumps at about age 50 and increases every year from there. This tells us that there’s something about younger people that is protecting them–could it be that younger people already had a vaccine that helped to protect them, even if it wasn’t specifically for COVID-19? After all, the combination vaccine for measles, mumps, and rubella (MMR) was introduced about 50 years ago.
Sure enough, a couple of studies have been making the rounds showing a link between the MMR vaccine and reduced COVID-19 death rates. The media (and social media) has jumped on these studies, even though they are not yet published or peer reviewed–because of course! Would it not be amazing if it turned out we *already have the vaccine we need* to prevent COVID-19?
But wait a second… let’s practice the skills we’ve been building in thinking critically about scientific information. Remember Lindsey’s Laws for sorting out the SOLID from the SENSATIONAL?
Her first law is that extraordinary claims require extraordinary evidence. [For those just joining the fun]
Perhaps the most well-publicized of the MMR/COVID-19 studies is a non-peer reviewed, unpublished manuscript. The authors (who are not infectious disease experts) make very strong conclusions about a causal link between MMR vaccine and immunity to COVID-19, even titling their paper, “MMR Vaccine Appears to Confer Strong Protection from COVID-19.” But this study, to be perfectly frank, fails Lindsey’s first law and a few others for fun. This is an extraordinary claim, and the evidence they provide is weak sauce.
They draw causal conclusions (causality: receiving MMR vaccination causes humans to become immune to COVID-19) from data that are only associational (association: people who have had MMR vaccination also have lower risk of death from COVID-19). In these kind of observed data, we cannot rule out the possibility that something else is different about people who have had the MMR vaccine that actually causes the benefit of reduced COVID-19 risk. Maybe MMR vaccine is more widespread in cheese-eating countries, and so people who get MMR vaccine also tend to eat a lot of cheese, and eating a lot of cheese confers COVID-19 immunity.
Okay that’s not really plausible, but here’s an example that is: possibly people who have had the MMR vaccine also tend to have health insurance, so they also tend to be hospitalized when they are in acute respiratory failure.
In addition, this study doesn’t look at individual-level vaccination. It relies on aggregated vaccine coverage rates and COVID-19 death rates for entire nations. So we have no idea if the people who were vaccinated with MMR are also the people who are less likely to die of COVID-19. We just know that nations with high vaccine coverage have lower COVID-19 death rates. Which honestly just supports the idea that some countries have better healthcare systems than others.
That said, there are a few hints about a biologically plausible mechanism by which a vaccine for a totally different virus could boost the immune system in a general way or partially signal the adaptive immune system to watch out for COVID-19. But there’s not a lot to write home about there so far.
Right now, scientists are doing much more robust laboratory-based and clinical trial studies of MMR vaccine’s ability to trigger the adaptive immune system or boost general immune responsiveness and protect against COVID-19 infection.
As the COVID-19 science website PreventEpidemics.org concludes in this excellent brief overview of the issue, “For now, there is no evidence to support giving additional doses of MMR vaccine as a COVID-19 prevention or treatment measure.”
