It May Be Possible to Catch the Coronavirus Twice, Scientists Believe

People who catch the novel coronavirus may be at risk of being reinfected, according to a team of scientists who have reviewed existing studies on different coronaviruses and immunity.

The researchers also warned COVID-19 could become a seasonal virus if a vaccine isn't developed.

Five months into the COVID-19 pandemic, more than 5.1 million cases have been reported, and 1.9 million people are known to have survived the disease, according to Johns Hopkins University. The U.S. is the country with the most known cases, as the graph below by Statista shows. One of the more pressing questions surrounding the little-understood coronavirus is whether a person is immune after catching it.

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The chart illustrates the 10 countries with the highest number of coronavirus cases as of May 22. Statista

To try to answer this question, scientists assessed 40 existing studies on the coronavirus family of bugs that SARS-CoV-2—which causes COVID-19—is a member of. The team looked at research on COVID-19-causing SAR-CoV-2, as well as SARS-CoV, the bug behind the 2002 to 2004 SARS epidemic; MERS-CoV of 2013's MERS outbreak; and four coronaviruses that cause common colds. The findings were published in the Journal of General Virology.

The immune system can take a few days to produce antibodies against any given invader. Evidence suggests most people who catch SARS-CoV-2 have an antibody response between 10 and 14 days after being infected. Antibodies are detected in some patients a long time after symptoms have passed, and not at all in a small number of cases in the timescales of those studies, according to the review.

Over time, antibodies to other coronaviruses fade, the team found. In cases of coronaviruses that cause common colds, people have been known to be reinfected after just 80 days. Therefore "reinfection of previously mild SARS-CoV-2 cases is a realistic possibility that should be considered in models of a second wave and the post-pandemic era," according to the team.

Modeling studies that have forecast the potential progression of COVID-19 cited by the team suggest that fading antibodies could have a "major impact" on whether SARS-CoV-2 will become an endemic coronavirus.

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People practice social distancing in white circles in Domino Park, during the Covid-19 pandemic on May 17, 2020, in the in Brooklyn borough of New York City. JOHANNES EISELE/AFP via Getty Images

If our immunity isn't permanent, as with coronaviruses OC43 and HKU1 that cause the common cold, "many epidemiological scenarios lead to SARS-CoV-2 becoming a seasonal human coronavirus, with either annual, biennial or sporadic patterns of epidemics over the next 5 years," they wrote.

But if we can engineer immunity with a vaccine, "models suggest that SARS-CoV-2 infection can be dramatically reduced or possibly eliminated."

"It is also unclear if reinfections will result in onward transmission, but that cannot be excluded," the authors said.

If a person doesn't build up protective antibodies to SARS-CoV-2, it is possible that other arms of the immune system may change the course COVID-19 takes, either by easing symptoms or making the infection worse at the moment the antibody response is starting up.

The authors called for studies measuring whether antibodies can neutralize the virus, categorized by age group and disease severity to be started as a matter of urgency. Researchers should also try to document whether people with mild COVID-19 and with low levels of antibodies have been reinfected.

Paul Kellman, professor of virus genomics at Imperial College London, said in a statement that other coronaviruses are a good place to start when trying to shed light on our immunity to SARS-CoV-2, but added: "We need to be cautious about inferring too much."

"We do not really know what happens on the pathway of a new coronavirus in humans becoming an endemic seasonal infection, but it could be that when the four seasonal coronavirus[es] first jumped from animals into humans they were much like SARS-CoV-2 in their transmission and pathogenesis.

"Over time, as population immunity to the seasonal coronavirus[es] became widespread, the amount of severe disease probably declines. However, seasonal coronavirus[es] can still cause pneumonia in some people," said Kellam.

Alain Kohl, deputy editor-in-chief of the Journal of General Virology, said in a statement: "Understanding immune responses to these viruses is on many people's minds—from the public hearing about vaccines, testing and antibodies, to policymakers, and scientists working on or with an interest in the current pandemic.

"This review gives an up-to-date, and superbly researched, overview of this field. Many people will find areas or topics of interest in this article, that should help them understand the important discussions going on. We are delighted to see it published in the journal."