A month after testing positive for COVID-19, a group of people with mild infections had protective antibodies in their blood, a new study has found.
The study, whose findings should be interpreted with caution as it has not yet been peer-reviewed or published in a medical journal, followed a group of 160 hospital staff in France who had tested positive for COVID-19 but did not require hospitalization.
The researchers found that nearly all the patients had measurable amounts of antibodies — material produced by the body as it fights off an infection – and that these antibodies were somewhat able to neutralize the virus. The neutralization appeared to increase over time, though how that translates to immunity isn’t clear.
“Although not yet demonstrated, several lines of evidence suggest that the presence of neutralizing antibodies may be associated with protective immunity for SARS-CoV-2 infection,” the study authors wrote.
But, as the study only looked at people for up to about a month after symptom onset, it doesn’t show whether antibodies will be present much longer than that, or if they confer immunity to the virus, how long that immunity might last.
“We know there is mounting evidence that people who get infected mount an immune response,” said Dr. Isaac Bogoch, an infectious disease specialist at Toronto General Hospital.
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“There’s very likely to be some degree of immunity to this infection for some period of time. It’s just not clear what the duration of time is,” he said.
There is growing evidence that people might develop some immunity if they’re infected, though it’s still a bit early to say.
An experiment done on macaques found that monkeys who recovered from the disease didn’t develop it again when they were re-exposed to the virus. It’s unclear whether this finding translates to humans, though.
It’s a key question, particularly when it comes to “serologic testing” — tests to determine whether someone has had the disease. Without knowing more about what kind of immunity the antibodies confer, it’s hard to know what to do with the results.
And, according to a recent update from the U.S. Centers for Disease Control and Prevention, current serologic tests might have very high rates of “false positives,” meaning that they show someone has had the coronavirus even if they actually haven’t.
In populations with a low prevalence of COVID-19, less than half of those who test positive might actually have antibodies, the CDC said. For that reason, it doesn’t currently recommend that serologic test results be used to determine whether someone should return to work, school, or other communal settings.
“Even if your serology test is positive and someone truly has antibodies, it doesn’t answer the question to what extent are they immune and how long are they immune,” Bogoch said.
More research is required to find out the answers to these questions, he said, but he’s hopeful they will be answered soon.
“We’re already reaching a point now where the first settings that experienced this infection are coming up to six months,” he said. “This is a perfect cohort to follow moving forward.
“We’re still in the midst of a global pandemic. People have been infected and they have recovered. Let’s see if they get reinfected.”
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