What do we know about each of the vaccines’ short-term safety?
Paul E. Sax, M.D.
Overall, both mRNA vaccines are quite safe — that’s the good news, and it should be the dominant message for our patients. But no vaccine (actually, nothing in medicine) is 100% safe.
Before discussing side effects, we need to acknowledge that the safety of Covid-19 vaccines will be in the spotlight for some time — these are new vaccines for a new disease. Rare events will appear in the news, amplifying attention and worry disproportionate to the actual risk. Our task will be to put these uncommon events into perspective, underscoring that these risks are far lower than the risk of getting sick with Covid-19.
These first two vaccines are classified as “reactogenic” — meaning that they will cause some side effects in most people who receive them, reflective of the brisk immune response they generate. In clinical practice, we should put these vaccines in the same side-effect category as the recombinant shingles vaccine (Shingrix) rather than the annual flu vaccine.
The most common side effect is
pain at the injection site, especially in the 12 to 24 hours after administration. Around 1% of participants in the trials categorized the pain as “severe.” Fatigue and headache are other relatively common side effects; high fevers are less common. These side effects generally resolve within a couple of days and are responsive to acetaminophen or a nonsteroidal antiinflammatory drug such as ibuprofen. In general, side effects are more common in younger vaccine recipients than in older ones, with the second shot inducing more side effects than the first.
Bell’s palsy was reported more frequently in vaccine recipients than in controls, but there was not a sufficiently large number of cases to conclude that this was beyond what would naturally be observed in populations of this size by chance. There were no cases of Guillain–Barré syndrome or transverse myelitis.
Although hypersensitivity occurred equally in the placebo and vaccine groups in both trials, after distribution of the vaccines in the United Kingdom and the United States, reports emerged of vaccine recipients experiencing severe allergic reactions (anaphylaxis) shortly after receiving their first dose. opens in new tab. The current leading suspect in causing these reactions is polyethylene glycol, a compound present in both vaccines. Because of these rare events, administration of the vaccines includes a period of 15 minutes of observation after vaccination — 30 minutes for those with a history of severe allergic reactions of any sort.
It’s critically important to emphasize that these allergic reactions are uncommon — the current estimate is that anaphylaxis will occur at approximately 1 in 100,000 doses. opens in new tab. Although this rate of severe allergic reactions is higher than that with other vaccines, it is substantially lower than the rate reported with penicillin, which is estimated to be 1 in 5000. But since severe penicillin allergies don’t turn up as news stories, our challenge will be to contextualize this risk. (Last reviewed/updated on 11 Jan 2021)
NEJM
https://www.nejm.org/covid-vaccine?query=pfw&jwd=000000762462&jspc=CD