(CNN) A large study involving close to 2 million people in Israel shows the Pfizer/BioNTech coronavirus vaccine slightly raises the risk of heart inflammation, swollen lymph nodes and shingles. But it also finds that Covid-19 infection raises the risk of heart inflammation even more -- plus it raises the risk of blood clots, heart attacks and other deadly events.
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.
"In this study in a nationwide mass vaccination setting, the BNT162b2 vaccine was not associated with an elevated risk of most of the adverse events examined," Dr. Ran Balicer of the Clalit Research Institute in Tel Aviv and colleagues wrote in their report, published in the New England Journal of Medicine.
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.
"Messenger RNA (mRNA) vaccines may be associated with myocarditis, but they can also prevent cases of myocarditis, acute kidney injury, arrhythmia, and thromboembolic disease," Lee, who was not involved in the study, wrote in a commentary.
"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.