How do we know if COVID-19 vaccines are safe?
Scientists look for security problems during the testing phase and continue to monitor as the shots spread around the world. So far, the only serious warning that has emerged is a rare risk of serious allergic reactions.
Different types of COVID-19 vaccines have been authorized and their possible side effects will be different for each one – although there is more public data on vaccines being launched in Western countries than elsewhere. Countries also vary in their vaccine standards, with some allowing injections to be used before the final stage test involving a large number of volunteers.
But in the United States, Britain and the European Union, regulators demanded that any vaccine be tested on tens of thousands of people before distribution. So far, the United States is using injections from Pfizer and Moderna, while Britain and Europe have eliminated those injections plus the AstraZeneca vaccine.
The large studies by these companies found that the common side effects were minor and typical of the accelerating immune system: arm pain, fever and flu-like symptoms, including fatigue, chills and headache.
But, since extremely rare problems may not appear even in large trials, vaccines are still being monitored. The US and UK governments and the European Medicines Agency track reports by health professionals and the public about suspected side effects. Extra scrutiny in the United States includes tracking insurance claims for warning signs. And recipients of the vaccine in the U.S. can sign up for a program that sends text messages to see if they are experiencing side effects.
These checks are reassuring.
People should wait for a short time after vaccination in case they have a severe allergic reaction, called anaphylaxis. Such incidents so far have been rare, with between 2 and 5 reports of anaphylaxis for every million doses of vaccine in the first few weeks of inoculations in the United States, according to the Centers for Disease Control and Prevention.
Officials expect to receive reports of health problems, even deaths, which occur only by chance in the days or weeks after vaccination, given the large number of people, including frail elderly people, being vaccinated.
Deaths and other serious events are investigated to see if the vaccine had any influence. The authorities consider the person’s general health and the frequency with which the reported condition occurs without vaccination. With more than 52 million doses of vaccines administered in the United States in mid-February, the CDC said it had detected no pattern of deaths that indicated a safety problem.