You need two doses of the Pfizer and Moderna vaccines to be fully protected against COVID-19. In the case of the Pfizer vaccine, guidelines established by the Food and Drug Administration say you must wait 21 days after your first shot to get the second, or “booster,” dose. With the Moderna jab, the shots are spaced at least 28 days apart.
But what if you miss that important second dose? According to Good Housekeeping, some people may be hesitant to return to get their second shot because they don’t want to wait in a long line again or had a bad reaction to the first shot.
Experts say it is vital for your immunity to complete the vaccination course. Dr. Nicholas Kman, an emergency physician at Ohio State University’s Wexner Medical Center, says getting both shots ensures as much immunity as possible against COVID-19. Research has shown that getting only one shot of the Pfizer drug, provides 52% defense against the spread of the virus and the first shot of the Moderna vaccine imparts 80% protection. But there are no clinical studies to show how long partial protection lasts. Kman says that while both vaccines do provide about 80% protection against a person becoming infected by the virus after the first dose, the second dose increases the number of antibodies in bloodstream tenfold, offering 95% efficacy.
Dr. Anthony Fauci, the director of the National Institute of Allergies and Infectious Diseases questions whether one shot of the vaccine can provide long-term immunity, said Good Housekeeping.
“When you leave it at one dose, the question is, how long does immunity last?” he asks. The infectious disease expert warns that with the new B.1.1.7 variant on the scene, “You’re in a tenuous zone if you don’t have full impact.”
If you do miss that second shot, Dr. Adam Ratner, a pediatric infectious disease expert at NYU Langone Health and a vaccine researcher, tells TIME that you should schedule one as soon as you can. While the three-to-four-week gap is recommended, the Centers for Disease Control and Prevention (CDC) says it’s okay to get your booster shot within 42 days of the first.
“Beyond that, we start to operate in an area where there’s simply less data,” explains Ratner. Experts say that it does not mean that the vaccine is less effective if given more than six weeks apart, it implies that we just do not have the clinical data to support the efficacy of a wider gap between doses. Many countries, including the U.K, are purposely delaying the second dose in order to give more residents at last one shot at immunization.
What you do not want to do is start over or mix and match your vaccines, say experts at the CDC. If you need to reschedule your second dose, even beyond the 42-day mark because you are feeling ill or your healthcare provider recommends you wait, you may still be fully protected.
“It’s reasonable to suspect that the vaccine remains effective if the series are spaced out farther,” Dr. Sachin Nagrani, medical director at Heal, in Washington D.C., tells Good Housekeeping. And Dr. Kman adds that “getting a different vaccine for your second dose may be theoretically possible, but certainly not studied or recommended. It would be better to wait to get the same manufacturer given that you do have good protection at the two-week point after your first shot.”