Although reports of reinfection from the novel coronavirus have been rare so far, public health experts worry that new variants of the virus may be less susceptible to natural immunity—meaning people who've recovered from a previous coronavirus infection may be at risk of reinfection by a new variant.

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Reported cases of coronavirus reinfection have been rare so far—but data constraints exist

Reported cases of reinfection from the novel coronavirus can occur, but they've been rare so far, according to the World Health Organization (WHO). Late last year, Maria Van Kerkhove, head of WHO's emerging diseases and zoonosis unit, said continuing research suggests immunity to the novel virus may last for at least six months. "In some people, it may wane after a few months, but we do get a good indication that natural infection immune response is lasting for some months," Van Kerkhove said.

However, Kerkhove cautioned, "[w]e're about a year into this pandemic, and so we still have a lot to learn." And as it stands, many questions regarding immunity to the novel coronavirus still haven't been answered definitively.

Along those same lines, it's not entirely clear just how many people have been reinfected with the novel coronavirus thus far, Kaiser Health News reports.

Cheat sheets: Population Health 101

According to a global tracker, officials have reported fewer than 50 substantiated cases of reinfection worldwide, including five cases in the United States. However, KHN reports that in the United States, "scientists' understanding of reinfection has been constrained by the limited number of U.S. labs that retain [coronavirus] testing samples or perform genetic sequencing."

According to a review of reinfection tracking efforts, "many U.S. states aren't rigorously tracking or investigating suspected cases of reinfection," KHN reports. And in states that are doing so, officials have identified and are investigating "far more potential cases [of reinfection] than previously anticipated," according to KHN.

Mark Pandori, director of Nevada's public health lab, told KHN, "I predict that we are missing cases of reinfection," adding, "They are very difficult to ascertain, so you need specialized teams to do that work, or a core lab."

Experts worry new coronavirus variants could increase risk of reinfection

According to KHN, scientists say efforts to determine how frequently coronavirus reinfections have occurred so far also could help researchers evaluate whether newly emerging variants of the novel coronavirus can subvert natural immunity, and therefore increase the risk that people who've already recovered from coronavirus infections could become infected again.

Scott Lindquist, Washington's state epidemiologist for communicable diseases, told KHN, "Those two areas, reinfection and variants, may cross paths."

Some experts believe that new coronavirus variants may be emerging in response to increased human immunity to earlier variants of the virus. For instance, research suggests that new coronavirus variants first discovered in Brazil, South Africa, and the United Kingdom have developed mutations that appear to make them more transmissible than earlier variants of the virus, as well as less susceptible to immunity acquired from earlier variants and current Covid-19 vaccines. And as Emma Hodcroft, a molecular epidemiologist at the University of Bern, recently told Vox, the variants discovered in Brazil and South Africa both have a mutation known as E484K that "might allow reinfection."

Cheat sheets: Evidence-based medicine 101

Some new research appears to support that theory, the Associated Press reports. For example, according to the AP, a recent study in South Africa found that 2% of the study's participants who had recovered from previous coronavirus infections became infected again with the new variant circulating in the country.

"What this basically tells us, unfortunately, is that past infection with early variants of the virus in South Africa does not protect" against the new variant, Shabir Madhi of the University of the Witwatersrand in Johannesburg, who worked on the study, said.

Similarly, researchers in Brazil have documented several cases in which people who'd recovered from previous coronavirus infections became reinfected with the new variant circulating there, the AP reports.

What does this mean?

Ultimately, experts say the threat of coronavirus reinfection means that people—including those who've recovered from a previous coronavirus infection—should continue practicing measures intended to curb the novel coronavirus's spread, such as wearing face masks and physical distancing.

Stuart Sealfon of Mount Sinai's Icahn School of Medicine, who has worked on research regarding novel coronavirus reinfections, told the AP, "Previous infection does not give you a free pass. … A substantial risk of reinfection remains."

In addition, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and chief medical adviser for the White House's Covid-19 response, said the potential for reinfection should serve as "an incentive to do what we have been saying all along: to vaccinate as many people as we can and to do so as quickly as we can." He added, "My looking at the data suggests ... and I want to underline suggests ... the protection induced by a vaccine may even be a little better" against the new variants than immunity provided by natural infection (Marchione, Associated Press, 2/8; Aleccia, Kaiser Health News, 2/8; Resnick, Vox, 1/27).