It is clear that coronavirus vaccines are safe and effective. But as more are rolled out, researchers are learning about the extent and nature of side effects.
- The two messenger-RNA (mRNA) vaccines, made by Moderna and Pfizer–BioNTech, seem to cause similar reactions. A significant portion of people experience non-serious reactions, such a sore arm or a headache. That proportion is larger than the one for the annual flu shot — perhaps because the mRNA COVID-19 vaccines generate a particularly strong immune response.
- A tiny number of people have experienced severe allergic reactions to the vaccines. These are extremely rare and no one has died. Fewer than five people per million doses administered of the Moderna or Pfizer–BioNTech experienced anaphylactic reactions. That is based on self-reported data from health-care workers and vaccinated individuals. For the Oxford–AstraZeneca vaccine, 30 cases of anaphylaxis have been confirmed so far, out of a little more than 3 million administered doses.
- Some researchers have had their eye on polyethylene glycol (PEG) as the anaphylaxis-causing agent in the mRNA vaccines. More research is needed.
- No deaths have been directly attributed to a COVID-19 jab. But it’s very hard to definitively link a death that happens days or weeks after the vaccine — especially among recipients who are very old or have serious health conditions.
- Safety data for some other widely used shots, such as the Chinese CoronaVac vaccine or the Russian Sputnik V vaccine, are harder to come by.