“I think this study adds to the growing evidence that, along with vaccination, daily physical activity is the single most important thing you can do to prevent severe COVID-19 outcomes,” said Robert Sallis, a family and sports medicine doctor at the Kaiser Permanente Fontana Medical Center in California and former president of the American College of Sports Medicine. He has researched covid and exercise but was not involved with the new study.
The study’s findings raise questions, though, about how much — or little — exercise might best magnify vaccine benefits and whether it is too late to benefit if you already have been fully vaccinated or will be soon.
A wealth of research in the past year has shown that being active and fit substantially lowers your risk of becoming seriously ill if you develop covid. Sallis led a study, for instance, of almost 50,000 Californians who tested positive for the coronavirus before vaccines were available. Those who had regularly walked or otherwise worked out before falling ill were about half as likely to need hospitalization as sedentary people.
Similarly, an August review of 16 past studies involving nearly 2 million people concluded that active people were substantially less likely than the inactive to be infected, hospitalized or killed by covid.
These connections between exercise and covid protection make sense, Sallis said. We know “that immune function improves with regular physical activity,” he said, as do lung health and inflammation levels, which otherwise can contribute to spiraling bad outcomes with covid.
But studies had not looked at whether active people gain additional benefits from their coronavirus shots and boosters.
So, for the new study, which was just published in the British Journal of Sports Medicine, researchers in Johannesburg gathered anonymized records of almost 200,000 men and women from the nation’s largest health insurer.
The records included information about people’s vaccinations, covid outcomes and exercise habits, gleaned from activity trackers and gym visits. Because the health insurer gave people points and prizes for being active, the study subjects tended to scrupulously record each workout.
The researchers first broadly compared the vaccinated and unvaccinated. (The Johnson & Johnson vaccine was the only available option then.) As expected, the unvaccinated developed covid and became seriously ill in much larger numbers than the vaccinated.
But even among the fully vaccinated, exercise made a significant difference in covid outcomes, said Jon Patricios, a professor of clinical medicine and health sciences at the University of Witwatersrand in Johannesburg-Braamfontein, who oversaw the new study.
Vaccinated people who walked or otherwise exercised moderately for at least 150 minutes a week were almost three times less likely to be hospitalized if they developed covid than those who were vaccinated but sedentary.
In more concrete terms, their vaccines protected them about 25 percent better than the same shots in sedentary people.
These people’s exercise habits met or exceeded the standard exercise guidelines promoted by the World Health Organization and the Centers for Disease Control and Prevention, Patricios said, which call for a half-hour or so of moderate activity at least five times a week.
But even vaccinated people who moved less, exercising for as little as an hour each week, were 1.4 times less likely to be hospitalized than the sedentary, vaccinated group, suggesting their vaccines were about 12 percent more effective than those of people who did not exercise.
“Doing something mattered, even if people weren’t meeting the full guidelines,” Patricios said. “It’s an idea we call ‘small steps, strong shield.’ ”
If you cannot fit in a 30-minute walk today, he said, a 10-minute walk is better than skipping exercise altogether.
This study was associational, though, meaning it shows links between activity and covid outcomes. While it does not prove that being active causes vaccines to be more effective, the links were consistent and the effects large, Patricios said.
He also believes the relationship would be similar for exercise and other coronavirus vaccines such as the Moderna and Pfizer versions, and in people who do not happen to live in Johannesburg.
How habitual activity augments vaccine response is still somewhat unclear. But Patricios suspects exercisers’ brawny immune systems prompt the creation of extra battalions of covid antibodies after each vaccination. Lifestyles might also affect response, including people’s diets and income.
Perhaps most encouraging, “I do not think it is ever too late” to start exercising, he said. Been inactive? A stroll today should begin prepping your immune system to respond with greater fervor to your next vaccination or covid exposure. “Plus,” he pointed out, “you don’t need a prescription, and it’s free.”
Do you have a fitness question? Email YourMove@washpost.com and we may answer your question in a future column.