John Whyte MD, MPH
Chief Medical Officer, WebMD
Why do I need more than one shot of the coronavirus vaccine? Both the Pfizer-BioNTech and Moderna vaccines require two doses to offer the full benefit. The first dose helps the immune system create a response against SARS-CoV-2, the virus that causes COVID-19. The second dose further boosts the immune response to ensure long-term protection.
Research shows that the vaccines are more than 50% effective 10 days or so after the first shot and nearly 95% effective several days after the second. Each vaccine requires different spacing between the doses. So it's really important to work with your doctor to get the timing right on the vaccine you are given.
And please make sure you get the second shot. I don't want you to think one is better than none. You do need both. The reality is that getting two shots isn't new to vaccines. Several vaccines require that, including for hepatitis B, HPV, and shingles.