Question: I was just reading this article published by the American Society of Microbiology. Could recent vaccination for other diseases help protect against COVID?
Answer: Ohh…. I’m glad to revisit this hypothesis now that there’s more information! In short, we still don’t know, but it’s seeming more plausible that live attenuated vaccines could offer some protection against COVID. We talked about BCG vaccination offering potential COVID protection a while back (see Q&A of 4/27). Since then, there have been several other reports, including an article on oral polio vaccine (OPV) and the article you cite on measles, mumps, rubella vaccine (MMR), about the plausibility of other live attenuated vaccines offering protection. Note: to my knowledge, scientists are arguing that existing live attenuated vaccines can serve as stop-gap measures in the context of no SARS-CoV-2 vaccine; everyone is still pushing for a SARS-CoV-2 vaccine!
As a reminder, live attenuated vaccines are those that use a weakened (attenuated) form of the virus to elicit an immune response. Because these types of vaccines create such a strong immune response, the protection they offer typically lasts a lifetime. What’s also fascinating about these types of vaccines (in my opinion) is that they not only allow a person’s body to develop antibodies against the specific virus, they also prompt an innate immune response that helps protect against other viruses! This article from Science published earlier this month, “Can existing live vaccines prevent COVID-19?”, does an amazing job laying out the evidence regarding the relationship between live attenuated vaccines, the innate immune response (for a refresher on the innate immune system, see our Q&A of 5/9), and long-term outcomes (e.g. reduced mortality). Scientists aren’t sure of the exact mechanisms by which live attenuated vaccines offer non-specific protection, but the long and short of it is that they seem to boost the immune system so it is better primed to quickly and effectively respond to virus invaders.
There are a number of BCG vaccine studies in the works now. I just checked clinicaltrials.gov and see that there’s also an MMR trial in the works out of the University of Cairo in Egypt and one OPV trial in the works out of the Bandim Health Project in Guinea-Bissau. The authors of the article published by the American Society of Microbiology state that they are also planning an MMR trial out of New Orleans.
If any live attenuated vaccine offers protection against COVID, we’d want to use the vaccine that is in the most abundant supply and has the fewest side effects. The authors of the article published in Science that I referenced earlier make a strong case for oral polio vaccine over BCG, arguing that OPV is safer, cheaper, in more abundant supply, and more likely to induce a common innate immunity reaction since both polioviruses and coronaviruses are positive-strand RNA viruses. Between OPV and MMR, I’m not sure which would be preferred. Finally, for a nice synthesis of SARS-CoV-2 vaccines, NPR published this piece earlier today.
Image 1. Oral Polio Vaccine, Haiti 2010 (image from USAID)
