It’s the first large study to compare the risks of vaccination versus infection head to head in the same population during the same time, and it shows the risks of infection far outweigh any risks from the vaccine, the researchers said.
They did find extra cases of myocarditis — a type of heart inflammation that’s been linked with both of the mRNA vaccines, made by Moderna and Pfizer. It added up to about three extra cases per 100,000 people vaccinated, and was seen almost entirely among young men.
“The main potential adverse events identified included an excess risk of lymphadenopathy (swelling of the lymph glands), herpes zoster infection (shingles), appendicitis, and myocarditis,” they wrote.
“To place these risks in context, we also examined data on more than 240,000 infected persons to estimate the effects of a documented SARS CoV-2 infection on the incidence of the same adverse events,” they added.
“SARS-CoV-2 infection was not estimated to have a meaningful effect on the incidence of lymphadenopathy, herpes zoster infection, or appendicitis, but it was estimated to result in a substantial excess risk of myocarditis.”
Covid-19 infection raised the risk of myocarditis by much more than vaccination did — about 11 cases per 100,000 people vaccinated, they found.
They also found some surprises.
“Some initially unexpected effects were seen in the results of the current study. The BNT162b2 vaccine appears to be protective against certain conditions such as anemia and intracranial hemorrhage,” they wrote. “These same adverse events are also identified in this study as complications of SARS-CoV-2 infection, so it appears likely that the protective effect of the vaccine is mediated through its protection against undiagnosed SARS-CoV-2 infection,” they added.
Dr. Grace Lee, a pediatrician at Stanford University who chairs the US Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices, said the findings provide valuable insight.
“The key to comparing these risks depends on the risk of SARS-CoV-2 infection to an individual person, and that risk can vary according to place and over time. Given the current state of the global pandemic, however, the risk of exposure to SARS-CoV-2 appears to be inevitable.”
Last June, the US Food and Drug Administration added a warning about risk of myocarditis and a related inflammatory condition called pericarditis to information sheets for the Covid-19 mRNA vaccines.
Doctors say it is important to diagnose the condition quickly but is easily treated and patients recover with little trouble.