Side effects coming with the second dose of the Moderna and Pfizer vaccines have increased so-called vaccine hesitancy. Some people are even hoping to get away with just one shot. But the National Institutes of Health is warning against stopping at one dose.

“When you just leave it at one dose, the question is, how long does it last?” Dr. Anthony Fauci, the director of NIAID, said. “And when you’re dealing with variants, you’re in a tenuous zone.”

Dr. Paul Offit, the director of the vaccine education center at Children’s Hospital of Philadelphia, urges people to get both shots despite the side effects associated with the second dose.

“Although it’s true the second dose can cause fatigue and fever and headache and muscle ache, it is a small price to pay to be protected against this disease for a more durable or longer length period of time,” Offit said.