The CDC recommends the second booster for those over 50 who received their initial booster shot at least four months earlier.
Scott Olson via Getty Images News
New data on the second booster suggests the older you are, the more you need it.
Understanding how much protection a vaccine offers is not as simple as it sounds.
Andriy Onufriyenko/Moment via Getty Images
For a number of reasons, as time goes on vaccines become less effective. So how do researchers calculate how well vaccines are working?
People getting vaccinated may still have questions about COVID-19 vaccines, like why it takes two doses — and then two weeks — to take full effect.
THE CANADIAN PRESS/Ryan Remiorz
A medical student answers questions he gets asked at a COVID-19 vaccine clinic: Efficacy versus real-world effectiveness, immune response and how the mRNA vaccines compare to vaccines already in wide use.
Vaccine efficacy statistics are often based on the results of randomized controlled trials.
Vaccine efficacy is usually expressed as a percentage, but what is it actually measuring? Statisticians explain what the numbers mean, and what they say about how well a vaccine can protect us.
AstraZeneca, Pfizer and Moderna appear equivalent in reducing your chance of serious illness from COVID-19.
China has administered more than one billion doses of its homegrown COVID-19 vaccines, the majority of which were developed by local companies Sinovac and Sinopharm. So what do we know about them?
Even if we came up with a definition of what makes the “best” vaccine, we don’t have the luxury of choice, when vaccines are in short supply.