How do we know that COVID-19 vaccines are safe?
Scientists look at safety issues during the testing phase and continue their monitoring as shots are fired around the world. So far, the only serious warning that appears is a rare risk of severe allergic reactions.
Different types of COVID-19 vaccines have been approved and the possible side effects will be different for each one – although there is more public information about the vaccines being rolled out in Western countries than elsewhere. Countries also vary in their vaccine standards, and some allow the use of shots before the final phase of testing involving large numbers of volunteers.
But in the US, Britain and the European Union, regulators have required any vaccine to be tested in tens of thousands of people before it can be distributed. So far, the US has used shots from Pfizer and Moderna, while Britain and Europe have cleared those plus the AstraZeneca vaccine.
The large studies of the companies found that common side effects are minor and are typical of the immune system that recovers: pain in the arm, fever and flu-like symptoms including fatigue, chills and headaches.
But since extremely rare problems can not arise even in large tests, the vaccines are still monitored. The US and British governments and the European Medicines Agency are stopping reports from health workers and the public about suspected side effects. Additional investigation in the US includes the detection of insurance claims for red flags. And recipients of U.S. vaccines can sign up for a program that sends text messages to see if they are experiencing side effects.
These checks are reassuring.
People are supposed to wait a short time after vaccination in case they have severe allergic reaction, called anaphylaxis. Such incidents have been rare so far, with according to the Centers for Disease Control and Prevention between 2 and 5 anaphylaxis reports for every million doses of vaccinations in the first weeks of U.S. vaccinations.
Officials are expected to receive reports of health problems, even deaths, which occur just by chance in the days or weeks after vaccination, given the large number of people, including frail elderly people, who are vaccinated.
Deaths and other serious events are being investigated to see if the vaccine plays a role. Authorities take into account the general health of the person and how often the reported condition occurs without vaccination. With more than 52 million doses of vaccine administered in the US in mid-February, the CDC has said it does not detect any patterns in deaths that indicate a safety problem.