How do we know the

COVID-19 vaccines are safe?

Scientists look for

safety issues during the testing phase and continue their monitoring as shots

roll out around the world. So far, the only serious warning to emerge is a rare

risk of severe allergic reactions.

Different types of

COVID-19 vaccines have been authorised and it’s possible side effects will

differ for each — although there’s more public data on the vaccines being

rolled out in Western countries than elsewhere. Countries also vary in their

vaccine standards, with some allowing the use of shots before final-stage

testing involving large numbers of volunteers.

But in the US,

Britain and European Union, regulators required any vaccine to be tested in

tens of thousands of people before distribution. So far, the US is using shots

from Pfizer and Moderna, while Britain and Europe have cleared those plus the

AstraZeneca vaccine.

Those companies’

large studies found that common side effects were minor and typical of the

immune system revving up: soreness in the arm, fever and flu-like symptoms

including fatigue, chills and headache.

But since extremely

rare problems might not turn up even in large tests, the vaccines still are

being monitored. The US and British governments and the European Medicines

Agency track reports filed by health workers and the public about suspected

side effects. Extra scrutiny in the US includes tracking insurance claims for

red flags. And US vaccine recipients can sign up for a program that sends text

messages to see if they’re feeling side effects.

Those checks are

proving reassuring.

People are supposed

to wait around 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 anaphylaxis reports for every million vaccine doses in the

first weeks of US inoculations, according to the Centers for Disease Control

and Prevention.

Officials expected

to receive reports of health problems, even deaths, that occur just by chance

in the days or weeks after vaccination, given the huge numbers of people,

including the frail elderly, getting inoculated.

Deaths and other

serious events are investigated to see if the vaccine played a role.

Authorities consider the person’s overall health and how often the reported

condition occurs without vaccination. With more than 52 million vaccine doses

administered in the US by mid-February, the CDC said it hasn’t detected any

patterns in deaths that signal a safety problem.