If you received your second dose of either the Pfizer or Moderna COVID-19 vaccine and experienced a sore arm and perhaps some fever, well, good for you.

“That’s typically a good sign,” said Fred Campbell, MD, an internal medicine physician and associate professor of medicine at UT Health San Antonio. “In general, a good local reaction is consistent with the body’s defense against that particular vaccine, which means the development of antibodies.”

But, he quickly added, everyone is different. If you don’t have a sore arm, “that doesn’t mean the vaccine is not working, it’s just that if you do it’s likely you’re getting a good response.”

Mild symptoms can begin immediately after getting the shot or within a few minutes or hours and can last a day or so, “but almost never for more than 36 hours,” Dr. Campbell said.

To relieve pain or soreness at the injection site, the Centers for Disease Control and Prevention recommends applying a cool, wet washcloth and exercising the arm. Drink plenty of fluids if you experience fever.

Another concern, Dr. Campbell added, is the time between the first and second doses. For the Pfizer vaccine, it’s recommended that the second dose be administered 21 days after the first. For Moderna, it’s 28 days.

But, he noted, those days are not set in stone.

“Because of the problems with supply and distribution,” Dr. Campbell said, “it appears now that it’s quite possible that you could receive the vaccine as late as six weeks after [the first dose]. And it’s clear that that provides the same level of protection as getting the second dose three or four weeks after.”

The vaccines will be most effective about 14 days after the second dose. Even then, people who have received the vaccines should continue to wear masks in public and practice physical distancing.

“The fact that these vaccines are extremely effective, better than 90% effective, nothing in medicine is 100%, except ‘do no harm.’ And doing no harm means to continue to wear the mask until advised by public health experts that we are at a point where we’ve achieved herd immunity and no longer have to worry about significant transmission of the virus.”