IMMUNITY AFTER COVID-19 STILL UNCERTAIN
Rna-based viruses may provide limited protection from reinfection
PARIS—EVEN as virologists zero in on the virus that causes the new coronavirus disease 2019 (COVID-19), a very basic question remains unanswered: do those who recover from the disease have immunity?
There is no clear answer to this question, experts say, even if many have assumed that contracting the potentially deadly disease confers immunity, at least for a while.
“Being immunized means that you have developed an immune response against a virus such that you can repulse it,” explained Eric Vivier, a professor of immunology in Marseilles.
A few months
“Our immune systems remember, which normally prevents you from being infected by the same virus later on.”
For some viral diseases, such a measles, confer immunity for life.
But for Rna-based viruses such as SARS-COV-2—THE bug that causes the COVID-19 disease—it takes about three weeks to build up a sufficient quantity of antibodies, and even then they may provide protection for only a few months, Vivier told AFP.
At least that is the theory.
In reality, the new coronavirus has thrown up one surprise after another, to the point where virologists and epidemiologists are sure of very little.
“We would expect that to be a reasonable period of protection, but it is very difficult to say with a new virus—we can only extrapolate from other coronaviruses, and even that data is quite limited,” said Michael Ryan, executive director of the World Health Organization’s Emergencies Program when asked how long a recovered COVID-19 patient would have immunity.
For SARS, which killed about 800 people across the world in 2002 and 2003, recovered patients remained protected “for about three years, on average,” Francois Balloux, director of the Genetics Institute at University College London, told AFP.
“One can certainly get reinfected, but after how much time? We’ll only know retroactively.”
A recent study from China reported on rhesus monkeys that recovered from SARSCOV-2 and did not get reinfected when exposed once again to the virus.
“But that doesn’t really reveal anything,” said Pasteur Institute researcher Frederic Tangy, noting that the experiment unfolded over only a month.
Positive again
Indeed, several cases from South Korea found that patients who recovered from COVID-19 later tested positive for the virus.
While it is not impossible that these individuals became infected a second time, Balloux said it was more likely that the virus never completely disappeared and remains— dormant and asymptomatic— as a “chronic infection.”
“That suggests that people remain infected for a long time—several weeks,” Balloux added. “That is not ideal.”
Another prepublication study that looked at 175 recovered patients in Shanghai showed different concentrations of protective antibodies 10 to 15 days after the onset of symptoms.
“But whether that antibody response actually means immunity is a separate question,” commented Maria Van Kerhove, technical lead of the WHO Emergencies Program.
“That’s something we really need to better understand—what does that antibody response look like in terms of immunity.”
Indeed, a host of questions remain.
“We are at the stage of asking whether someone who has overcome COVID-19 is really that protected,” said Jean-francois Delfraissy, president of France’s official science advisory board.
For Tangy, an even grimmer reality cannot be excluded.
“It is possible that the antibodies that someone develops against the virus could actually increase the risk of the disease becoming worse,” he said, noting that the most serious symptoms come after the patient had formed antibodies.
Faced with all these uncertainties, some experts have doubts about the wisdom of pursuing a “herd immunity” strategy.
“The only real solution for now is a vaccine,” Archie Clements, a professor at Curtin University in Perth, Australia, told AFP.