Several European countries have now suspended use of the AstraZeneca COVID-19 vaccine over concerns about blood clots.
The connection between the vaccine - which has not been approved for use in the U.S. - and the blood clots is still unclear. The World Health Organization has said the vaccine is safe to use.
I think it’s also showing a great deal of being conservative about how we deploy these vaccines,” said Dr. C. Buddy Creech, director of Vanderbilt University’s vaccine research program, who said the rate of blood clots among people who received the shot is not any higher than would be expected in the general population.
The AstraZeneca vaccine went through clinical trials and was approved for use in several countries before concerns about the blood clots arose.
"When we launch a vaccine, we don’t just stop looking for side effects," Dr. Creech explained. "In fact, we start employing even more ways to look for any rare events that may occur when we start giving to more than we could ever do in a clinical trial."
He says that in the U.S., vaccine producers, doctors and public health agencies are continuously investigating the effects of the Pfizer, Moderna and Johnson & Johnson vaccines even after they were given emergency use authorization by the FDA.
Some side effects are anticipated and normal, such as arm pain, fever, chills, fatigue and headache.
Aside from those, there are two main categories of harmful side effects that health experts are watching for.
"The first main group are those that happen in the hours following vaccinations," said Dr. Creech. This includes allergic reactions.
“The second group that we see is in the month or month and a half following vaccination where we might see different types of responses,” such as a drop in blood count or neurological issues.
Dr. Creech told KCBS Radio's "Ask An Expert" that researchers such as himself are constantly monitoring large health systems such as Kaiser for reports of any issues that may arise after someone is vaccinated to look for potential side effects or patterns. Additionally, there are reporting systems set up for smaller systems and individual doctors to submit information.
The CDC has also set up its own reporting site called V-safe, for members of the public to self-report.
Dr. Creech said this makes it possible for experts and public health agencies to see any potential issues in close to real time and pull vaccines if necessary.
"When we have multiple options it allows us to move different products in and out,” he said. "Whatever it will take to promote the health of our populations, that’s what we should be doing."
But at this point, he added there is nothing for people to be afraid of.
"Now that we’ve gotten three months or so under our belts from the Pfizer and Moderna vaccines, we really are maintaining that confidence in safety."
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