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(CNN) --
Being repeatedly sick with COVID-19 appears to increase a person's chances of facing new and sometimes long-lasting health problems after their infection, according to the first study on the health risks of reinfection.
The study, which is based on the health records of more than 5.6 million people treated in the Veterans Administration Health System, found that compared to those with a single Covid-19 infection, those with had two or more documented infections had more than double the risk of dying and triple the risk of being hospitalized within six months of their last infection.
They also had a higher risk of lung and heart problems, fatigue, digestive and kidney disorders, diabetes and neurological problems.
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The results come at a time when a new wave of coronavirus variants, in particular the omicron subvariant BA.5, has become dominant in the United States and Europe, causing a new surge in cases and hospitalizations.
The BA.5 subvariant caused about 54% of cases across the country last week, doubling its share of covid-19 transmission in the last two weeks, according to data released Tuesday by the Centers for Disease Control and Prevention. US Diseases (CDC).
The BA.5 subvariant has key mutations that help it evade antibodies generated by both vaccines and previous infection, leaving many people vulnerable to reinfection.
Dr. Ziyad Al-Aly, a clinical epidemiologist at Washington University in Saint Louis, led the research, which was published as a preprint before peer review.
Al-Aly relates that he decided to do so after observing that reinfections were becoming more frequent among his own patients.
"If you were to ask me about the reinfection a year and a half ago, I would say that maybe I had a patient here or there, but it was very, very rare," Al-Aly said.
However, that is no longer true.
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"So we asked ourselves a simple question: If you've already been infected with COVID and now you're on your second infection, does it really add risk? And the simple answer is yes."
Calculation of risks due to reinfections
Al-Aly and his team compared the health records of more than 250,000 people who had tested positive for COVID-19 once with the records of another 38,000 who had two or more documented COVID-19 infections in their medical records.
As a control group, more than 5.3 million people without a record of covid-19 infection were used.
Among people with reinfections, 36,000 had two Covid-19 infections, about 2,200 had contracted Covid-19 three times, and 246 had been infected four times.
The most common new diagnoses following reinfections included chest pain, abnormal heart rhythms, heart attacks, inflammation of the heart muscle or the pericardium (a sac-like membrane that surrounds the heart), heart failure, and blood clots.
Among the most common lung problems were shortness of breath, low oxygen in the blood, lung disease and fluid buildup around the lungs, Al-Aly said.
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The study found that the risk of a new health problem was highest at the time of reinfection with COVID-19, but also persisted for at least six months.
The increased risk was present whether or not he had been vaccinated, and it was gradual, that is, it increased with each subsequent infection.
Al-Aly said that's not what people really think will happen when they get Covid a second or third time.
"There's this idea that if you've had Covid before, your immune system is trained to recognize it and is better equipped to fight it off, and if you get it again, it might not affect you as much, but that's not really true," he said.
Al-Aly said that doesn't mean there aren't people who have had covid and are fine;
there's a lot.
Rather, what his study shows is that each infection carries a new risk, and that risk accumulates over time, he said.
Even if a person has half the risk of developing lasting health problems during a second infection than during the first, he said, they still have a 50% higher risk of problems than someone who didn't get sick with Covid-19 a second time.
The study has some important limitations.
Al-Aly says reinfections are more common among people who are already at risk because of their age or health.
That shows that reinfection may not be random, and it could be that the health risks associated with reinfections are not random either.
"Sicker individuals or people with immune dysfunction may be at increased risk of reinfection and adverse health outcomes after reinfection," Al-Aly said.
The doctor was not interested in trying to isolate the pure effects of reinfection, but rather wanted to understand how repeated infections affect the people who contract them.
"The most relevant question for people's lives is: if you get reinfected, does it increase the risk of acute complications and prolonged covid, and the answer is a clear yes and yes," he said.
The study is observational, which means it cannot be used to determine a cause-and-effect relationship.
Al-Aly says the researchers saw these increased risks even after weighting the data to account for the effects of a person's age, gender, medication use, and underlying health before becoming ill with COVID-19.
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Experts not involved in the research say it's compelling.
"I think a lot of people have this idea that if you've survived the first infection, the second time you'll be fine. There should be no problem,'" said Dr. Daniel Griffin, an instructor of clinical medicine at Columbia University.
"The conventional wisdom, true, is that reinfections are mild, nothing to worry about, nothing to see here," Griffin said of the study on the "This Week in Virology" podcast.
But that is not being confirmed, she said.
That's not how it's supposed to work.
Even when viruses change form, like the flu, our immune systems often retain the memory of how to recognize and fight off a part of them.
They may still get sick, but the idea is that our previous immunity is there to mount some kind of defense and prevent us from serious harm.
With coronaviruses, and especially the SARS-CoV-2 coronavirus, the blows keep coming.
"A year later, you can get re-infected with the same coronavirus a second time. It's not clear that that second infection could be milder, because coronaviruses inherently have the ability to interfere with lifelong immunity," Griffin told CNN. .
Griffin says he has seen Covid-19 reinfections both ways.
Sometimes the second or third is easier for your patients, but sometimes not.
How does this compare to other respiratory infections?
At the beginning of the pandemic, people would get sick from covid and three months would go by where they were fairly protected, he said.
But now, those reinfections are more frequent, no doubt due to the rapid changes of the virus.
He says that he has recorded some people who have been infected four times in the last two years.
"We don't really record a lot of that with the flu," Griffin said.
As for what people should do now about this risk, Dr. Michael Osterholm, who directs the Center for Infectious Disease Research and Policy at the University of Minnesota, says that Americans no longer want to know more about the pandemic, however, this does not mean that the pandemic will no longer continue.
Osterholm said he has three close friends who recently went to a restaurant for the first time since the pandemic began.
All of them tested positive within 72 hours of that visit to the restaurant.
If you're at higher risk of getting sick or just want to avoid getting sick, now's a good time to wear an N95 mask in public places, he says.
"People don't want to hear it, but it's the reality. We're seeing this resurgence and there are more and more vaccine failures. It's clearly a big concern," he says.
-- Deidre McPhillips of CNN Health contributed to this report.
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