Billions of dollars are being invested in the development of vaccines against the coronavirus. Until one arrives, many scientists have turned to tried-and-true vaccines to see whether they may confer broad protection, and may reduce the risk of coronavirus infection, as well.
Old standbys like the Bacille Calmette-Guerin tuberculosis vaccine and the polio vaccine appear to help train the immune system to respond to a broad variety of infections, including from bacteria, viruses and parasites, experts say.
Now a study suggests that people who have received certain routine vaccines in the recent past — including childhood vaccinations like measles-mumps-rubella and polio, as well as adult flu vaccines — have lower coronavirus infection rates than those not recently vaccinated.
But many experts greeted the conclusions with skepticism. The paper, an analysis of electronic health records from the Mayo Clinic, was posted online; it has not been through the peer review process and has not been accepted by a medical journal.
Critics pointed to numerous methodological problems. It is a retrospective study; as such, it points to an association between vaccinations — a marker of overall good health and healthy behaviors — and lower infection risk.
But the study does not prove a cause-and-effect relationship. While scientists generally consider studies like these useful for generating hypotheses that may be worth exploring further, they are far from definitive.
The researchers analyzed the immunization records of 137,037 patients who had been tested for infection with the coronavirus, comparing matched pairs of vaccinated and unvaccinated patients who were otherwise similar.