You have been vaccinated and recently had covid-19, so you don鈥檛 have to worry about catching it again, right? Wrong. A large study suggests that every time a person is reinfected, they have additional health risks, both during their immediate illness and in the months afterwards.
鈥淓very reinfection is like rolling the dice again,鈥� says at VA St. Louis Health Care System in Missouri. 鈥淎 second infection is still bad for you.鈥�
These findings are especially concerning because the omicron subvariants BA.4 and BA.5, which are driving the latest wave of cases in much of the world, are even better at evading prior immunity than the BA.1 and BA.2 subvariants that caused the first omicron waves. Many millions of people worldwide could therefore be reinfected in the coming weeks.
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The study gained a lot of attention online when it was . Among other things, it found that people with two or more covid-19 infections were twice as likely to die of any cause and three times as likely to be hospitalised in the six months after catching the coronavirus, compared with people who caught it just once.
This was widely misinterpreted as reinfections being worse than first infections. That absolutely isn鈥檛 the case, says Al-Aly.
The risk of serious outcomes after reinfections is probably smaller than after the first infection, he says. We can鈥檛 be certain, however, as the study compared people who had been infected at least twice with those who had been infected just once, rather than comparing first and second infections in the same individuals. It is possible that those who were infected twice were especially vulnerable and more likely to be severely affected, says Al-Aly.
Some have argued all the study shows is that getting a second or third covid-19 infection is covid-19 just once. To some extent, this is true.
While this may seem obvious to some, others assume reinfections will be harmless. Nobody had quantified the effect of reinfections before, says Al-Aly, or shown that people remain worse off for at least six months after the reinfection.
In the study, people who had second or third covid-19 infections had significantly higher rates of everything from heart disease to kidney disorders during the first 30 days of infection, as well as in the months that followed, than people with just one infection, suggesting a cumulative increase in risk. This was true both for those who were unvaccinated and for those who received at least one dose before catching covid-19 for the second time.
The study was based on the health records of nearly 6 million people, maintained by the US Department of Veterans Affairs. Of these, nearly 260,000 people had one covid-19 infection and 40,000 had two or more.
Across the study, the average age of the people was 60, but many were as young as 20, says Al-Aly, who doesn鈥檛 think the results apply only to older people.
One criticism of the study is that it defined reinfections as a positive test 30 days or more after a previous positive test, which could be a persistent initial infection rather than a reinfection. That criticism is entirely fair, says Al-Aly. The team has since reanalysed the data looking only at positive tests that occurred at least 90 days after the first, and the results are essentially the same, he says.
Overall, these findings shouldn鈥檛 be a big surprise given what we know about the risk of reinfection with other viruses. For instance, flu reinfections occasionally cause serious complications, from heart inflammation to multi-organ failure, especially in older people.
Flu reinfections result in a huge global disease burden. It wouldn鈥檛 be surprising if 鈥� for the next few years, at least 鈥� covid-19鈥檚 burden is even higher, due to higher numbers of reinfections and possibly greater risks with each reinfection.
So what should we do? Given there is a reduced appetite for wearing masks and limiting social contact, Al-Aly says we should be giving more people preventative treatments, such as Pfizer鈥檚 Paxlovid (made up of the generic drugs nirmatrelvir and ritonavir), while prioritising the development of more effective vaccines, like nasal ones.
鈥淭here is simply no excuse for why these vaccines are not being hyper-aggressively pursued,鈥� at the Scripps Research Translational Institute in California . 鈥淭he lack of priority and resource allocation stems from the illusion that the pandemic is behind us.鈥�
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