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On the same day President Donald Trump suggested he is protected from the coronavirus after his bout with COVID-19, researchers showed that a person can be infected with the virus twice.
"I went through it. Now they say I'm immune," Trump said at a campaign rally in Florida Monday. "I feel so powerful."
But in a new study, scientists detail the case of a Nevada man who tested positive for coronavirus, recovered, and contracted the virus again weeks later.
The evidence not only raises questions about how long immunity lasts after infection, but it also raises the possibility that a vaccine will not provide permanent protection.
"It is totally irresponsible for the president to go around claiming that he's immune," said Andrew Pavia, chief of the pediatric infectious diseases division at the University of Utah, who was not part of the new study. "That's just not something that we can say with any scientific certainty."
Writing in the journal The Lancet Infectious Diseases, scientists describe the case of a 25-year-old man who was infected on two separate occasions about six weeks apart.
The man first developed a sore throat, cough, headache, nausea and diarrhea in late March. Testing at a community event in Reno on April 18 found he had COVID-19, the disease caused by the coronavirus.
Symptoms cleared up by late April. He tested negative twice in May.
But at the end of May he got sick again, this time worse than before. He had to go to the hospital and needed supplemental oxygen.
That's when he came to the attention of Mark Pandori, director of the Nevada State Public Health Laboratory and co-author of the new study.
"We had our antenna up for it," Pandori said.
Early on in the pandemic, he said, he and his colleagues knew that the possibility of reinfection was one of many big questions facing health officials.
When the patient's name came through the public health system's records a second time, they went back to his first swab and compared the genetic code of the two viruses. They were two different variants.
Fourth published case
The case is the first reinfection in North America to be confirmed, but other cases have been published from Hong Kong, Belgium and Ecuador, and others are suspected.
Though only four cases of reinfection have been confirmed, it's not clear how common it is.
"While this seems rare, we really don't know because we're not out there looking very closely for it," Pandori said.
It's not clear why the Nevada patient had a worse illness the second time. The first patient with documented reinfection, a man from Hong Kong, had no symptoms the second time.
"The Hong Kong case made us hope that repeat infection would be milder than the first infection," said Rajesh Gandhi, an infectious diseases physician at Harvard Medical School and co-author of COVID-19 treatment guidelines at the National Institutes of Health and the Infectious Diseases Society of America. He was not part of the current study.
"Maybe [the Nevada patient] got just a bigger dose of the virus the second time around," Gandhi said. "Or maybe there's something about his immune system that didn't allow it to fight it off the second time."
Scientists don't have the answers yet, he added.
It's also possible that the second virus was different in some significant way.
"That seems less likely," Pavia, of the University of Utah, said. "But we are learning more every day and it pays to be humble."
Some viruses generate lifelong immunity after one infection, but others do not. The virus that causes COVID-19 is part of a large family of coronaviruses, including some that cause the common cold. Immunity to these viruses wanes after a year or two.
Experts say the growing evidence for reinfection suggests that immunity to the COVID-19 virus may be temporary.
Pavia said that this argues against a strategy known as herd immunity, which allows the virus to burn through the population unchecked in order to bring on immunity quicker. Some of Trump's health advisers recommend this approach.
"Even if the entire population were to develop natural immunity, with the millions and millions of deaths that would be the result of that strategy, that immunity will fade for many people over time," Pavia said. "And so, the virus can return."
It also suggests that "even a pretty effective coronavirus vaccine would need to be repeated year in year out," he added.
Nevada's Pandori is more optimistic. He notes that vaccines work differently from natural infection.
"While the bad news may be that our system gets tricked by this thing, we still have really good reasons to believe that vaccinology will win," Pandori said.
In the meantime, he said, people who have recovered from COVID-19 need to keep their guard up. Even if they are reinfected and have no symptoms, it's unclear whether they can spread the virus to others.
"There is no invulnerability, necessarily," he said. "We have to not only protect our own individual selves, but to protect those around us. We have to continue to be vigilant and act as though we've never had it."