Data from 11,000 healthcare workers in the U.K. found that people who have been infected with COVID-19 may have immunity from symptomatic infection for at least six months.
Researchers tested the workers who developed COVID-19 during the first wave of the virus last spring to see if any of them got symptoms during the second wave, in the fall. While some of them did have symptoms, none tested positive for the virus up to six months later.
According to the Daily Mail, of the 1,038 hospital staff members who became infected with the disease, only 128 developed COVID-19-like symptoms and none tested positive. When looking at the total 11,000 healthcare workers recruited in the study, not one registered a positive test after they had been infected by the virus.
“We conclude that SARS-CoV-2 infection appears to result in protection against symptomatic infection in working age adults, at least in the short term,” said the researchers. There have been a few reports of re-infection, however, including the case of a Dutch cancer patient in her 80’s who died after she battled COVID-19 for the second time.
Experts note that the U.K. study that was conducted in Newcastle only tested healthcare workers who developed symptoms so those who were asymptomatic could have become reinfected with the disease and spread it to others. According to Hartford HealthCare, about 30% of people with COVID-19 have no symptoms.
A previous U.S. study from the Icahn School of Medicine at Mount Sinai found that 90% of people who recover from COVID-19 have immunity for at least five months. While that contradicts an earlier study from the Imperial College of London that said antibodies decline more than 26% within three months, the American scientists said they found just the opposite conclusion. In fact, they suggested that immunity could last for years.
Professor Florian Krammer, a virologist at Icahn who lead the study team, said in a statement that “more than 90% of people who were mildly or moderately ill produce an antibody response strong enough to neutralize the virus, and the response is maintained for several months,” according to CNN.
The researchers explained that the sustained levels of immunity they observed came from long-lived cells in the bone marrow which is a typical response seen in other viruses. The drop off in antibodies noted in other studies likely came from the first responders, the plasmablasts, that launch the initial attack against pathogen invaders and then wane, according to CNN.
The team published their findings in the journal Science, adding that in working with antibodies generated from other human coronaviruses, these antibodies can last for years “and provide protection from reinfection or attenuated disease, even if individuals get reinfected.”