Covid vaccination cut risk of adverse heart events, large study finds

Recent Covid vaccination appears to have broad cardioprotective effects, according to a new study , which found reduced risk of events like heart attacks and stroke, hospitalization, and death in people who had received the vaccine.

The study, published in JAMA Internal Medicine on Monday along with several other Covid-related papers, followed more than 1 million veterans who received flu vaccinations at Veterans Affairs health care facilities in 2024; about a third of them also received a Covid vaccine.

Infection with SARS-CoV-2 is known to increase the risk of adverse cardiac events. In the eight months after the veterans were vaccinated, the researchers found, those who received Covid vaccines (either mRNA or another type) had a roughly 38% lower risk of Covid-associated major cardiovascular events. This benefit was greatest for those 75 and older and those with chronic conditions like kidney and lung disease.

To the researchers’ surprise, Covid vaccination was also tied to a nearly 24% reduction in all-cause cardiac events — not just those with a documented Covid diagnosis. The authors said this could translate to prevention of approximately 3,500 major cardiac events and 2,400 deaths annually per 1 million people.

Ziyad Al-Aly, a doctor and clinical researcher at Washington University in St. Louis, who led the study, chalks this up to higher rates of Covid infections in the broader community. He spoke to STAT about cases where individuals who felt “under the weather” did not test for Covid at the time, but then weeks later ended up in the emergency room with a cardiovascular event. “What that really means is that those [events] are actually likely related to SARS-CoV-2, that were never recognized to be so in the first place,” he said.

Robert Califf, a cardiologist and former commissioner of the Food and Drug Administration, wrote an accompanying commentary on Al-Aly’s findings. Califf spoke to STAT about why Covid vaccination may protect the heart saying, “There are many, many studies now that show that vaccinations of various types seem to reduce the risk of chronic diseases, including cardiovascular disease … this is not inconsistent with what the other studies have shown.” He agreed with Al-Aly’s thoughts, saying, “it’s also worth keeping in mind that the testing environment has changed a lot, so knowing for sure who had a subsequent infection, that’s probably the shakiest of the whole thing.”

Al-Aly stressed to STAT that Covid is still prevalent in the general population. “Despite the fact that the virus has evolved and things have mellowed down, and we no longer think of Covid infection as consequential, there is still actually a tidal wave of SARS-CoV-2 that continues to circulate in the population,” he said. “Much of it is only unrecognized, leading to heart problems. Much of it is unlinked or unattributed to SARS-CoV-2, because people are not testing.”

While Al-Aly’s findings indicate cardioprotective benefits of Covid vaccines, these results may surprise some because vaccine-related myocarditis — inflammation of the heart muscle — was an early concern about mRNA formulations. The side effect was seen mostly in young men . Notably, studies have found that vaccine-related myocarditis is significantly milder than myocarditis resulting from an actual Covid infection.

Researchers have described multiple potential connections between Covid and heart health, including increased inflammation triggered by the infection and direct damage to heart tissues from the virus. Infection also increases risk of long Covid , or other persistent symptoms. Nevertheless, Covid shot uptake in older adults is less than half that of the uptake of flu vaccines.

“I think when you have more than half of the population, even high risk, who are not electing to get updated, people are not viewing it as a medical necessity and a way to prove what the risks and benefits are would be to do large randomized trials. I thought the new NIH was going to answer those kinds of questions, but it doesn’t seem to be doing that,” said Califf.

Another new study in JAMA Internal Medicine , led by Ryan Wiegand and researchers at the Center for Disease Control and Prevention, evaluated the effectiveness of 2024-2025 Covid vaccines in the U.S. Among those who were vaccinated, there was a reduced likelihood of Covid-associated emergency room or urgent care visits. For adults 18 years and older, vaccine effectiveness was 41% against critical illness.

Bill Hanage, a professor of epidemiology at Harvard University not involved in these studies, told STAT he found it striking that “over the short term, the Covid vaccines in the Wiegand study are roughly as effective as flu vaccines.” He added,  “It is only recently that influenza has overtaken Covid as the most significant respiratory cause of illness and death in the United States. And it’s worth mentioning that those were pretty bad flu seasons. Covid vaccines are still protec…