Coronavirus: Recovery may not confer immunity, warn experts

PARIS/SANTIAGO • Even as virologists zero in on the virus that causes 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 immunised means that you have developed an immune response against a virus such that you can repulse it," said Dr Eric Vivier, a professor of immunology in the public hospital system in Marseilles.

"Our immune systems remember, which normally prevents you from being infected by the same virus later on."

For some viral diseases such as measles, overcoming the sickness confers immunity for life.

But for RNA-based viruses such as Sars-CoV-2 - the scientific name for 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, Dr Vivier told Agence France-Presse.

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 do not have the answers to that - it's an unknown," said Dr Michael Ryan, executive director of the World Health Organisation's (WHO) health emergencies programme, when asked how long a recovered Covid-19 patient would have immunity.

For severe acute respiratory syndrome, which killed about 800 people across the world in 2002 and 2003, recovered patients remained protected "for about three years, on average", said Professor Francois Balloux, director of the Genetics Institute at University College London.

"One can certainly get reinfected, but after how much time? We'll only know retroactively."

Several cases from South Korea showed that patients who recovered from Covid-19 later tested positive for the virus. But there are several ways to explain that outcome, scientists said.

While it is not impossible that these individuals became infected a second time, there is little evidence that this is what happened.

More likely, the virus never completely disappeared in the first place and remained - dormant and asymptomatic - as a chronic infection, said Prof Balloux.

Dr Ryan said he is not sure whether the presence of antibodies in blood gives full protection against reinfection with the coronavirus.

"A lot of preliminary information coming to us right now would suggest quite a low percentage of the population have seroconverted (to produce antibodies).

"The expectation that... the majority in society may have developed antibodies - the general evidence is pointing against that, so it may not solve the problem of governments," he added.

Meanwhile, Chile plans to issue immunity cards from tomorrow to people who have recovered from Covid-19, to signal that they are no longer contagious and can return to work and their normal lives, said Health Minister Jaime Manalich.

The measure may prove controversial as some of the cards will be based on the presence of antibodies to the virus, for which countries have struggled to mass produce reliable tests.

AGENCE FRANCE-PRESSE, REUTERS, BLOOMBERG