The Pfizer-BioNTech COVID-19 vaccine has no association with a broad range of potential adverse events — except for a rare heart problem, according to a nationwide study in Israel.
Over a 42-day follow-up period, vaccination was linked to 3.2% risk of experiencing myocarditis (a type of heart muscle inflammation). But the risk ratio of myocarditis was much higher — 18% — in people who contracted COVID-19, investigators said.
The data, from 2.4 million vaccinated persons, came from the largest healthcare organization in the country. The researchers evaluated the excess risk of lymph node swelling, herpes zoster infection, appendicitis, and myocarditis tied to vaccination. To put these findings in clinical context, they also estimated the effects of SARS-CoV-2 infection on the incidence of the same adverse events in more than 240,000 Israelis.
SARS-CoV-2 infection itself did not have any meaningful effect on the incidence of these adverse events except for myocarditis, which was substantial, they found. But SARS-CoV-2 may greatly increase the risk of other adverse events that vaccination is not linked to, Noam Barda, M.D., of Clalit Research Institute in Israel, and colleagues found. These include arrhythmia, acute kidney injury, pulmonary embolism, deep-vein thrombosis, myocardial infarction, pericarditis and intracranial hemorrhage, they reported.
Perhaps the most compelling finding is the substantial protective effect the vaccine had against a host of other clinical problems, probably because infection was prevented, commented Grace M. Lee, M.D., M.P.H., of Stanford University, who was not involved in the study.
It is important to note that adverse events linked to vaccination cannot be directly compared to those associated with contracting COVID-19, the researchers cautioned. Getting a shot is a single contained event, while becoming ill has many more potential ramifications, including the risk of transmitting the infection to family members and others, they explained.
The takeaway? Vaccination with Pfizer’s shot resulted in increased odds of only a few adverse events over a 42-day follow-up period. Most of the events were mild, although some of them, such as myocarditis, could be potentially serious, Barda and colleagues concluded.
“However, our results indicate that SARS-CoV-2 infection is itself a very strong risk factor for myocarditis, and it also substantially increases the risk of multiple other serious adverse events,” they added.
Full findings were published in the New England Journal of Medicine.