Virus World

There are now several cases of people becoming reinfected with Covid-19. But experts stress that’s not cause for panic. Here’s how to assess the news. Following the news this week of what appears to have been the first confirmed case of a Covid-19 reinfection, other researchers have been coming forward with their own reports. One in Belgium, another in the Netherlands. And now, one in Nevada. What caught experts’ attention about the case of the 25-year-old Reno man was not that he appears to have contracted SARS-CoV-2 (the name of the virus that causes Covid-19) a second time. Rather, it’s that his second bout was more serious than his first.  Immunologists had expected that if the immune response generated after an initial infection could not prevent a second case, then it should at least stave off more severe illness. That’s what occurred with the first known reinfection case, in a 33-year-old Hong Kong man.  Still, despite what happened to the man in Nevada, researchers are stressing this is not a sky-is-falling situation or one that should result in firm conclusions. They always presumed people would become vulnerable to Covid-19 again some time after recovering from an initial case, based on how our immune systems respond to other respiratory viruses, including other coronaviruses. It’s possible that these early cases of reinfection are outliers and have features that won’t apply to the tens of millions of other people who have already shaken off Covid-19.  “There are millions and millions of cases,” said Michael Mina, an epidemiologist at Harvard’s T.H. Chan School of Public Health. The real question that should get the most focus, Mina said, is, “What happens to most people?” But with more reinfection reports likely to make it into the scientific literature soon, and from there into the mainstream press, here are some things to look for in assessing them.

What’s the deal with the Nevada case?

The Reno resident in question first tested positive for SARS-CoV-2 in April after coming down with a sore throat, cough, and headache, as well as nausea and diarrhea. He got better over time and later tested negative twice.  But then, some 48 days later, the man started experiencing headaches, cough, and other symptoms again. Eventually, he became so sick that he had to be hospitalized and was found to have pneumonia. Researchers sequenced virus samples from both of his infections and found they were different, providing evidence that this was a new infection distinct from the first.

What happens when we get Covid-19 in the first case?

Researchers are finding that, generally, people who get Covid-19 develop a healthy immune response replete with both antibodies (molecules that can block pathogens from infecting cells) and T cells (which help wipe out the virus). This is what happens after other viral infections. In addition to fending off the virus the first time, that immune response also creates memories of the virus, should it try to invade a second time. It’s thought, then, that people who recover from Covid-19 will typically be protected from another case for some amount of time. With other coronaviruses, protection is thought to last for perhaps a little less than a year to about three years. But researchers can’t tell how long immunity will last with a new pathogen (like SARS-CoV-2) until people start getting reinfected. They also don’t know exactly what mechanisms provide protection against Covid-19, nor do they know what levels of antibodies or T cells are required to signal that someone is protected through a blood test. (These are called the “correlates of protection."

Why do experts expect second cases to be milder?

With other viruses, protective immunity doesn’t just vanish one day. Instead, it wanes over time. Researchers have then hypothesized that with SARS-CoV-2, perhaps our immune systems might not always be able to prevent it from getting a toehold in our cells — to halt infection entirely — but that it could still put up enough of a fight to guard us from getting really sick. Again, this is what happens with other respiratory pathogens. And it’s why some researchers actually looked at the Hong Kong case with relief. The man had mild to moderate Covid-19 symptoms during the first case, but was asymptomatic the second time. It was a demonstration, experts said, of what you would want your immune system to do. (The case was only detected because the man’s sample was taken at the airport when he arrived back in Hong Kong after traveling in Europe. “The fact that somebody may get reinfected is not surprising,” Malik Peiris, a virologist at the University of Hong Kong, told STAT earlier this week about the first reinfection. “But the reinfection didn’t cause disease, so that’s the first point.” The Nevada case, then, provides a counterexample to that....

A 25-year-old Nevada man appears had coronavirus twice, researchers say. Genetic tests indicate the patient was infected with two different varieties of the virus, a team at the University of Nevada Reno School of Medicine and the Nevada State Public Health Laboratory reported.  The patient was first diagnosed with coronavirus in April after he had a sore throat, cough, headache, nausea and diarrhea, the researchers wrote in a pre-print study posted Thursday. He got better around April 27, and he tested negative for the virus twice afterwards.  He continued to feel well for about a month. Then on May 31 he sought care for fever, headache, dizziness, cough, nausea and diarrhea. Five days later, he was hospitalized and required ongoing oxygen support. He was tested again for Covid-19 and the results were positive.