The exercising volunteers then rode a stationary bike or walked rapidly for 90 minutes after their vaccinations, either at the lab or outside on the sidewalks near the Covid vaccine sites. They worked out at a mildly challenging pace, aiming to keep their heart rates between about 120 and 140 beats per minute. But the researchers also asked some of the flu-shot volunteers to ride for only 45 minutes, to see if the shorter workout might be equally effective at amping immunity.
Because antibody levels tend to build in the weeks following a vaccination, the researchers drew blood from everyone again two and four weeks after their shots. (People getting the Covid vaccine received their second shot in the interim, since a second Pfizer shot should be given three weeks after the first.)
45 minutes is not enough.
After a month, everyone’s antibody levels to the flu or Covid shot rose substantially, as expected after getting a vaccine. But they were highest in the men and women who had exercised for 90 minutes afterward. This antibody bonus was not huge. “But it was statistically significant,” said Marian Kohut, a professor of kinesiology and member of the Nanovaccine Institute at Iowa State, who oversaw the new study.
People who exercised also did not report additional side effects after their shots. (They did not experience fewer side effects, either.)
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Covid boosters. Data released by the Centers for Disease Control and Prevention showed that booster shots against the coronavirus lose much of their potency after about four months, adding to evidence suggesting that some Americans may need a fourth dose.
Interestingly, 45 minutes of exercise in this study was not enough to bump up antibodies. The shorter workout probably did not increase the levels of substances needed to amplify immunity, including interferon alfa, Dr. Kohut said.
The researchers also repeated the flu vaccine experiment in mice that either jogged afterward or stayed still. The researchers checked their blood for interferon alfa levels and found them higher with exercise. But if the scientists chemically blocked production of the substance, the animals gained a little extra antibody benefit from exercise, suggesting exercise improves vaccine response in part by first raising interferon alfa levels.
The upshot of the results, then, is that “if you have the time and a safe place to exercise after your vaccination,” a moderate 90-minute exercise session may make your vaccine response greater, Dr. Kohut said, without adding to side effects.