Sporadic reports of Covid-19 patients seemingly becoming reinfected with the coronavirus have sparked doubts about whether people can ever gain immunity against the pathogen—and although current research suggests reinfection within a short time frame is unlikely, some researchers are hesitant to completely dismiss the idea.

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Doctors' stories, new studies raise concerns about coronavirus immunity

Since the coronavirus pandemic began, there have been reports from doctors throughout the world about recovered Covid-19 patients seemingly becoming reinfected with the novel coronavirus, leaving some people doubting whether humans can become immune to the virus.

For instance, a physician in New Jersey has claimed that at least two of his Covid-19 patients had recovered from and tested negative for the coronavirus for months, but then started again experiencing symptoms of the disease and tested positive. One of those patients began showing symptoms of Covid-19 again after attending a party. "So that is … reinfection," the doctor said.

The physician said the second recovered patient who appeared to be reinfected was a family member of the first patient. According to the doctor, that patient had tested negative for the coronavirus for several weeks, and even had developed enough antibodies to the virus that he was able to donate plasma for experimental Covid-19 treatments before again experiencing symptoms of the disease.

Further, some recent studies also have sparked questions about coronavirus immunity. For example, results from a study recently released in preprint that hasn't yet been peer reviewed showed that antibodies developed against the coronavirus in people who'd been infected declined significantly within two to three months post infection.

Moreover, Elitza Theel, director of the infectious diseases serology laboratory at the Mayo Clinic who was not involved in the study, said researchers are finding that coronavirus "antibodies will peak at about 20 to 30 days after symptom onset, and then they decline," and "[t]hey seem to decline much more rapidly in individuals that were asymptomatic or had mild forms of the disease."

Given that antibodies help to neutralize the coronavirus and are believed to provide people with immunity against the pathogen, those findings have raised alarms among some observers that people may gain natural immunity to the coronavirus for only a few months.

Robert Glatter, an assistant professor of emergency medicine at Lenox Hill Hospital and Northwell Health, explained that, if people could become reinfected with the coronavirus within a short period of time, it would mean that people may need to receive multiple vaccinations against the virus throughout the year to control the coronavirus' spread.

"It would definitely be a predicament for public health, there's no question about that," especially if there isn't a vaccine against the virus, said Kamran Kadkhoda, medical director of immunopathology at the Cleveland Clinic. "In the absence of a vaccine, the main thing that we'd have against reinfection are these prevention measures" such as physical distancing and face masks, Kadkhoda explained.

Research suggests coronavirus reinfection is unlikely

But despite the anecdotal reports from doctors about patients becoming reinfected with the coronavirus, researchers say there's no evidence supporting the notion that people can become reinfected with the virus within a short time period.

"I haven't heard of a case where it's been truly unambiguously demonstrated," said Marc Lipsitch, an epidemiologist at the Harvard T.H. Chan School of Public Health.

For instance, South Korea's Center for Disease Control and Prevention in one study confirmed that, among 285 cases of people who again tested positive for the coronavirus two months after receiving their initial positive test results (including some who were experiencing Covid-19 symptoms two months after their initial diagnoses), none of the patients' new samples contained enough virus particles to allow researchers to grow the virus from the samples in a lab. Researchers said those results indicated that the patients weren't actively infected with the virus, and the diagnostic tests likely had detected dead virus particles that remained in their bodies or generated false-positive positive results.

Further, the researchers noted that none of the patients who re-tested positive for the coronavirus transmitted the pathogen to others.

"It was pretty solid epidemiological and virological evidence that reinfection was not happening, at least in those people," Angela Rasmussen, a virologist at Columbia University, said.

As for studies showing that antibodies for the novel coronavirus decline over time, researchers say that's how antibodies work for a host of viruses.

Michael Mina, an immunologist at Harvard University, said although those studies have left some people "scratching their heads saying, 'What an extraordinarily odd virus that it's not leading to robust immunity,' … they're totally wrong."

"It doesn't get more textbook than this," he added.

And some research has resulted in different findings regarding coronavirus antibody levels over time. For example, results from a separate study that were released preprint and haven't been peer reviewed found that 120 patients who were infected with the coronavirus and experienced mild or moderate symptoms of Covid-19 had stable levels of coronavirus antibodies for at least three months post infection—and in some cases, those levels increased over that time.

In addition, even if someone who had been infected with the coronavirus didn't develop antibodies for the pathogen, a person's T-cells and B-cells could fight off reinfection, public health experts say.

"Even if you don't have a very high level of antibodies, you may be able to respond very rapidly to a challenge and nip it in the bud," said Michel Nussenzweig, head of the laboratory for molecular immunology at Rockefeller University. "You may be able to produce a better … faster response the second time around."

Ultimately, Monica Gandhi, a professor of medicine and associate chief of infectious diseases at the University of California-San Francisco, said, "No one is yet believing in reinfection since there is no good scientific report on it."

So why do some people experience Covid-19 symptoms twice?

So why, then, do some people seemingly recover from Covid-19 but again experience symptoms later?

Clinicians say more research is needed to answer the question of why some patients appear to fall ill with Covid-19 more than once, but some believe that such patients simply relapse because the coronavirus lays dormant in their bodies and reemerges—an occurrence that's been seen with some viruses that often result in lifetime immunity, such as the chickenpox virus, according to Daniel Griffin, an infectious diseases doctor and researcher at Columbia University Medical Center.

It also may be possible that some patients experience a long course of infection that ramps up months after they first contract the coronavirus and initially experience symptoms of Covid-19, some experts have said. And others have speculated that some patients may contract a different virus with similar symptoms to Covid-19 and assume they've been reinfected with the coronavirus.

But 'no one wants to dismiss the possibility' of reinfection completely

However, while most experts say they don't think it's likely people can contract the coronavirus more than once within a short period of time, "no one wants to dismiss the possibility" of reinfection altogether, Gandhi said.

And Griffin noted that, if researchers eventually find two different versions of the novel coronavirus' genetic code in one patient's body, it could point to two separate infections.

"This is one of those things I really don't want to be true," Griffin said, "[b]ut a lot of us are starting to say, 'I'm willing to entertain it as a possibility. Let's keep our eyes out and start watching'" (Johnson/Cha, Washington Post, 7/22; Resnick/Irfan, Vox, 7/22; Mandavilli, New York Times, 7/22; Craig, Monmouth Daily Voice, 7/9; Sternlicht, Forbes, 5/19).