How Vaccine Side Effects Compare to COVID Symptoms

The COVID-19 vaccines have become somewhat notorious for their side effects: fatigue, sore arm, maybe a fever. In a few rare cases, there are more serious complications, like inflammation of the heart. So is it riskier to get a vaccine or to take your chances with COVID itself?

A new study in the New England Journal of Medicine set out to answer this question, comparing the moderate to serious symptoms people experience after the Pfizer vaccine with those that people experience with a COVID infection. (Mild reactions like fever and soreness at the injection site weren’t included.) Here’s what they found:

• People who got COVID were at substantially higher risk for arrhythmia (irregular heartbeat), myocardial infarction (heart attack), deep-vein thrombosis (blood clots in places like the legs), pulmonary embolism (blood clots in the lungs), myocarditis (inflammation of the heart muscle), pericarditis (inflammation of tissues near the heart), intracerebral hemorrhage (bleeding in the brain), and thrombocytopenia (low platelet counts).
• People who got the vaccine were at substantially higher risk for lymphadenopathy (swollen lymph nodes).

The study was conducted as a medical records analysis in Israel, and it compared 884,828 vaccinated people with an equal number of unvaccinated controls, and 173,106 people with a COVID infection and an equal number of controls. (Each person was matched to a control of the same age, sex, home location, and health status.)

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Vaccine safety: We compared excess adverse events after #COVID19 vaccination (Pfizer-BioNTech) and after documented #SARSCoV2 infection.https://t.co/PNyCTqkq0t

Take-home message: Low excess risk of adverse events after vaccination, higher after infection.

Some thoughts???? pic.twitter.com/pbpJwCRd3D

— Miguel Hernán (@_MiguelHernan) August 25, 2021

The vaccine involved was the Pfizer one, so this analysis may not apply to other vaccines like the AstraZeneca. The Moderna vaccine is very similar to Pfizer’s, so it’s likely the results would be similar if the same study could be done with that vaccine — but without the numbers, we don’t know for sure.

“What is even more compelling about these data is the substantial protective effect of vaccines with respect to adverse events such as acute kidney injury, intracranial hemorrhage, and anemia, probably because infection was prevented,” writes Grace Lee, a professor of medicine at Stanford who penned an editorial commentary on the study.

She also notes that the best way to compare risk would include the chance of being exposed to COVID; if it were a rare disease, you’d be much more likely to get a serious adverse event from the vaccine than from being infected, which could change the risk/benefit calculus. But the way the Delta variant is currently raging, COVID is not a rare disease at all.

She writes: “Given the current state of the global pandemic, however, the risk of exposure to SARS-CoV-2 [the virus that causes COVID] appears to be inevitable.”