Scientists look for potential safety concerns during the testing phase and remain vigilant as vaccination campaigns around the world progress. For now, the only serious warning that has emerged is a rare risk of a serious allergic reaction.
Several types of coronavirus vaccines are licensed, and the side effects can vary between them, although there is more publicly available data on vaccines being developed in Western countries than in the rest of the world. There are also differences between countries’ vaccination standards, and some allow for inoculation of some in their final phase of trials with a large number of volunteers.
But in the United States, Great Britain and the European Union, regulatory agencies require each vaccine to be tested on tens of thousands of people before distribution. Currently, the United States uses those of Pfizer-BioNTech and Moderna, and Great Britain and Europe have also given the green light to that of AstraZeneca and the University of Oxford.
The large studies of all three found that common side effects were minor and typical of the immune system response: arm pain, fever, and flu-like symptoms such as fatigue, chills, and headaches.
But since extremely rare problems do not show up in even the largest studies, vaccines remain under control. The US and UK governments and the European Medicines Agency follow reports from health professionals and the public about possible side effects. In the United States, there is additional research, including tracking insurers’ claims for potential warnings. In addition, those who get the injection there can participate in a program that sends them messages to check if they notice any symptoms.
These checks have proven to be reassuring.
After receiving the injection, people should stay in the center for a while in case they develop a severe allergic reaction called anaphylaxis. Until now, these cases have been rare, with between 2 and 5 per million vaccines given in the first weeks of the US campaign, according to the Centers for Disease Control and Prevention (CDC) country.
Authorities expect to receive reports of health problems, and even deaths, that happen to occur in the days or weeks after vaccination, given the large number of people, including older people with more fragile health, who are vaccinated.
The deaths and other serious cases are being investigated to see if the vaccine played a role. Authorities look at the person’s general health and the frequency with which the problem occurs without the vaccine. With more than 52 million vaccines administered in the United States by mid-February, the CDC said it has found no patterns in deaths that indicate a safety concern.