For every million shots of the Pfizer and Moderna vaccines, between 2 and 5 cases of anaphylaxis have been reported. According to newly published data from the CDC, serious allergic reactions remain extraordinarily rare, and they’re treatable.
In December 2020, the US Food and Drug Administration (FDA) issued Emergency Use Authorizations for 2 mRNA-based vaccines: the Pfizer-BioNTech COVID-19 vaccine and the Moderna COVID-19 vaccine . Shortly after each authorization, the vaccines underwent the “most intensive safety monitoring in U.S. history,” the CDC said on its website. So far, the vaccines seem to be behaving admirably.
In the first days of the vaccination, a handful of anaphylaxis reports raised concerns, but reassuring data from more shots came in, showing that anaphylaxis rates are in line with those from other vaccines. The Pfizer vaccine seems to have a rate of 4.7 anaphylaxis cases / million of doses, while the Moderna vaccine has a rate of 2.5 cases/million doses administered. For comparison, the flu shot has a rate of 1.3 / million, while other vaccines have a rate up to 25 cases / million.
The CDC records and follows all side effects after vaccines — from mild to very serious. The agency says that mild allergic reactions such as hives, wheezing and swelling, can occur, and those who have had such a reaction to the first dose should also not get the second. However, specialists are more interested in severe side effects, especially severe allergic reactions.
Not only are these severe side effects exceedingly rare (a rate of 0.0003%), but they are also very treatable. All but one happened within 11 minutes of vaccine administration, and all 66 persons were treated in health care settings. Although 18 patients were hospitalized in intensive care, they were all alright in the end — and this is out of a rate of 18 million doses.
These aren’t just the first mRNA vaccines developed for COVID-19 — they’re the first mRNA vaccines in history. This is exciting because it opens up a new avenue for vaccines, not just for COVID-19 but other diseases as well. The fact that mRNA vaccines are safe shows great promise.
Encouraging data also came from the UK, where a similar analysis showed that severe side effects are also extremely rare, and the most common side effects are by far represented by things like headaches or a sore arm. In Israel, where over half a million people have received both doses, there were also no fatalities — and Israeli data shows a 92% effectiveness rate at preventing disease, consistent with the results originally published by Pfizer.
So far, COVID-19 has killed more than 474,000 Americans. The Pfizer and Moderna vaccines are more than 90% effective at preventing illness after two shots, which strongly shows that the benefits of vaccination outweigh the risks. Most agencies recommend not taking the vaccine only if you have a history of severe allergy. Still, even in the very unlikely case that anaphylaxis does happen, it is typically manageable.