Why You Need Two Doses of the COVID-19 Vaccine

Both the Pfizer and Moderna COVID-19 vaccines require two doses, three to four weeks apart for maximum protection. Experts say, while getting double doses might be a hassle, it is needed to have maximum protection against the virus.

According to Bustle, Dr. John A. Sellick, a professor at the Jacobs School of Medicine and Biomedical Sciences at the University of Buffalo, "the first dose primes the immune system and the second dose boosts it to give high level protection."

Both vaccines use genetic, mRNA technology to teach the body's immune system to make antibodies against the SARS-CoV-virus that causes COVID-19. Multi-dose vaccines are not new, according to Bustle, and the HPV vaccine requires three doses. Experts say, while the first dose trains your body to produce the correct antibody response, subsequent doses jog the immune system's memory so it does not forget, and in fact, produces stronger antibodies for longer protection.

Sellick said both Pfizer and Moderna tested different configurations to find the most effective way to provide immunity and decided, based on those tests, to develop the two-dose system. In fact, a study in December, published in The New England Journal of Medicine, stated the first dose of the Pfizer vaccine was only 52% protective. After the second shot, efficacy jumped to 91%, and a week later was 95% effective against COVID-19.

According to The New York Times, Dr. Paul Offit, a member of the Food and Drug Administration's advisory board, explained the second shot does not have to be given precisely in the three-week window.

"The second shot can be picked up at any time after the first," he said. "No need to start the series over."