The researchers speculate that the athletes' immune systems have been boosted and refined by the daily physical demands and damage of exercise so that they can respond so effectively to the vaccine.
While these results were remarkable, they did not address the acute effects of exercise and the question of whether a single high-intensity exercise could positively or negatively affect the body's responses to a vaccine. For the second of the new studies, published in Medicine & Science in Sports & Exercise in July, the scientists reverted to the same data, but focused only on the athletes' immune responses.
They compared the number of immune cells and antibodies in the athletes who got the flu shot within two hours of their last training session with those of the athletes who were shot one day after their last training session. If intense training weakens immune responses, the first group of athletes is expected to show fewer new immune cells than those who got their shot after a long break.
However, the researchers found no differences. Regardless of whether the athletes were vaccinated almost immediately after training or a day later, their immune responses were the same. Previous strenuous exercise had not decreased or increased the response.
Together, the two studies tell us that good form can increase our protection from vaccination, no matter how hard or when we exercise before the shot, says Dr. Sester.
Of course, these studies have focused on elite competitive athletes, who most of us are not. Dr. However, Sester believes that even more casual amateur athletes are likely to respond better to flu vaccines than sedentary people. Likewise, she and her colleagues expect that high fitness should improve the immune response to other vaccines, including possibly a Covid-19 shot.
"The basic principles of the vaccine response are probably the same," she says. However, future studies need to confirm this possibility when a vaccine becomes available.