Why did they pause the vaccine trial?

You have probably heard that there are several vaccine trials going on right now. Scientists are working hard to develop a vaccine for COVID-19. A vaccine will be an important public health measure we can take to protect ourselves. 

Why was a vaccine trial stopped?

You may have heard that one of these vaccine trials, the one testing the vaccine developed by AstraZeneca, was temporarily stopped due to an adverse event in one of the participants. 

Prior to beginning any vaccine trial, scientists develop rules about when to temporarily stop the trial in case of safety concerns. Recently, a participant had a severe adverse event, or SAE. Researchers needed to investigate this event to see if it had anything to do with the experimental vaccine. The company concluded the trial was safe to resume in the UK on September 12th. Trials elsewhere remain paused.

What is an adverse event?

Any time there is a big clinical trial with lots of participants, some people will happen to get sick. This is called an adverse event, and it may or may not be related to the study. Generally, when severe adverse events happen, the trial is stopped while the scientists investigate the illness. If scientists determine that the adverse event was due to the trial, they may consider ending the study. If they are confident that the study is safe, they will resume the trial. 

In the case of the Astra Zeneca trial, the patient developed a condition called transverse myelitis. Transverse myelitis is a rare but serious condition that can have many different causes, such as infections or autoimmune disorders. It is not yet known what caused the condition in the patient who got sick.

Does this mean the vaccine could make me sick?

There is good news here: The pause means that vaccine scientists are making safety a top priority. Scientists will continue to work hard to make sure that any vaccine they make is safe and effective for everyone

Last update: October 9, 2020, 5:38 pm ET

Science review: GSN, JAB