COVID-19 Antibodies Appear to Last for at Least Two Months, Preliminary Study Shows

COVID-19 patients have been found to carry antibodies to the coronavirus for almost two months after falling sick, in a preliminary study. However, it is unclear whether the antibodies could protect the patients from being reinfected.

Scientists looked at the blood samples of 177 people who had caught the coronavirus which causes COVID-19. They found most patients had antibodies that were detectable for up to around 60 days after they were infected by the coronavirus. But between 2 to 8.5 percent did not.

The findings were submitted as a pre-print to the website medRxiv, meaning the study hasn't been through the rigorous peer review process required to publish in scientific journals. Releasing studies this way enables scientists to spark debate on a topic.

The group of participants included a range of COVID-19 patients, with 19 percent not showing symptoms when they tested positive, but were diagnosed when they were being treated for other conditions. A total of 94 percent of the patients were hospitalized with COVID-19, a quarter whom died. Some 73 percent of patients had at least one underlying health condition, which is known to be a risk factor for complications.

In past studies, antibodies have been linked to more serious infections. The authors of the new paper found those who did have antibodies were more likely to have COVID-19 symptoms, be older (at 65 versus 41 years old, on average) and were more likely to have at least one underlying health condition—such as high blood pressure—as well as a higher body mass index (BMI). High blood pressure and obesity are known to be risk factors for more severe COVID-19.

Patients who had antibody responses were also more likely to have markers of inflammation in the body. This process in turn is linked with an overreaction of certain immune cells that are thought to raise a person's risk of dying of COVID-19.

What the team described as "non-white" people had a higher chance of having more antibodies and being ill enough to be hospitalized, the team found. This finding mirrored past research suggesting that higher antibody levels are linked with disease severity, and that people of black and ethnic minority backgrounds are more likely to die of COVID-19.

Antibodies aren't the only weapon the immune system has in its arsenal against germs like the coronavirus, and the authors believe those who didn't create antibodies may have fought off the germ in a different way. Another potential explanation is that these patients may have had mild infections which stayed in the mucosal cells of the respiratory tract, where other arms of the immune system dominate antibody responses.

The authors acknowledged their study was limited for a number of reasons, including that most of the patients were hospitalised. More research is needed to document antibody levels in patients with less severe infections, they said.

Co-author Professor Sanjeev Krishna at the St George's, University of London in the U.K., said in a statement: "Our results provide an improved understanding of how best to use viral and antibody tests for coronavirus, especially when not every person exposed to the virus will have a positive response."

Daniel M. Davis, professor of immunology at the University of Manchester who did not work on the paper, told Newsweek: "Understanding how antibody production varies among people is vital for many reasons, not least in learning how to treat people appropriately."

Six months into the COVID-19 pandemic which has killed over 437,000 people in more than 8 million cases, it remains unclear whether people who catch the virus are protected against future reinfections.

Davis, the author of The Beautiful Cure, a book about the immune system, said: "Crucially, the mere presence of antibodies in a person's blood doesn't signify whether or not a person is really protected from being re-infected.

Addressing the differences in white and non-white participants, he said: "There could be any number of reasons for this, especially because only a small number of people were tested. Also, it's not clear whether such a small difference would have any biological consequence in itself."

Davis said: "Importantly, this study has not been peer-reviewed and must be taken as preliminary."

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Blood samples to test for COVID-19 antibodies sit on a table at a clinic in Moscow on May 15, 2020. VASILY MAXIMOV/AFP via Getty Images