A recent study in the Lancet Medical Journal found that the effectiveness of a COVID-19 vaccine declines after a few months, signaling the need for booster shots.

Dr. Shad Marvasti of the University of Arizona College of Medicine says those with chronic illness, as well as those in jobs that often deal with face-to-face communication, should consider getting a booster shot as soon as possible.

“And if you’re a person who is out there more, a more public-facing job, you’re at higher risk for a breakthrough infection even if you’ve been fully vaccinated,” said Marvasti.

The study showed that after five months, the Pfizer vaccine was 73% effective at preventing COVID infections and 90% effective at preventing hospitalizations for those who are fully vaccinated.

Marvasti says the Moderna vaccine elicits a higher immune response that does not wain as much as the Pfizer vaccine.