Why you shouldn’t forgo your second COVID-19 vaccine dose

More than 35% of the U.S. population is fully vaccinated for COVID-19, according to the Centers for Disease Control and Prevention (CDC). And for anyone who receives the Moderna or Pfizer COVID-19 vaccines, two doses are required to complete the series and be fully vaccinated.

The CDC released a study earlier this year that revealed nearly 5% of the people who received the first dose of those vaccines did not receive the second dose within the recommended interval — 21 days for Pfizer and 28 days for Moderna.

"To get the maximum protection that's been demonstrated in the trials, we know that you're not considered fully protected until two weeks after your second dose of vaccine. And so that's why we really encourage everyone to make sure they get that second dose in," says Nipunie Rajapakse, M.D., a Mayo Clinic pediatric infectious diseases specialist.

The CDC is identifying and addressing possible barriers to completing the COVID-19 vaccination series. Dr. Rajapakse says clinical trials for the Moderna and Pfizer COVID-19 vaccines have shown that they are most effective when people take the full two-dose series.

"The first dose acts as a primer for your immune system. So it's the first chance to practice recognizing the infection and to practice making some antibodies," says Dr. Rajapakse. "And the second dose is usually what we call a booster dose. It really gives a chance for the immune system to kind of rev up and really ramp up that antibody production. And that's why it's really important to get that second booster dose, because that's where you get the high levels of protective antibodies generated."

Dr. Rajapakse adds that it's important to recognize that someone is not considered fully vaccinated and protected from COVID-19 until two weeks after the second dose of the Moderna or Pfizer COVID-19 vaccines. And even if you are beyond the recommended intervals of 21 or 28 days between vaccine doses, you can and should receive your second dose.

Learn how to schedule your COVID-19 vaccination, and read more about COVID-19.

Information in this post was accurate at the time of its posting. Due to the fluid nature of the COVID-19 pandemic, scientific understanding, along with guidelines and recommendations, may have changed since the original publication date.