Anyone who has survived Covid-19 is initially immune – at least that’s what epidemiologists have assumed so far. But reports of patients who got the disease again cause uncertainty. What is the current state of research?
Reports from Asia have caused a stir in the past few days, according to which patients who have already been cured have again been tested positive for the coronavirus. Is it possible that they weren’t immune after all? Can you catch the virus twice? So far there is no clear answer.
However, epidemiologists hope that an infected patient will be immune for at least a few months after recovery. “Being immune means that the body has developed a defense reaction against a virus. And because this immune reaction has a ‘memory’, it means that it later prevents infection with the same virus,” explains immunologist Eric Vivier from the university hospital in Marseille.
In general, it takes around three weeks for RNA viruses, which include Sars-CoV-2 in addition to the newer influenza pathogens, to produce enough protective antibodies, says Vivier. Experience has shown that this protection lasts for several months.
Rhesus monkeys develop resistance
So far the theory is – but the new Sars-CoV-2 is still too little researched to be sure. “We don’t know,” said WHO emergency director Mike Ryan, who directs the global fight against the virus. “We can only draw conclusions from our knowledge of other corona viruses, and even with them, our data are limited.”
When almost 800 people died worldwide during the Sars epidemic from November 2003 to summer 2003, the patients were “protected for an average of two to three years after their recovery,” explains François Balloux, an expert from University College London. “So you can get infected again, but the question is: after what time?” He adds: “We will only know that afterwards.”
A recent Chinese study with rhesus monkeys gives hope: the animals infected with the virus showed themselves to be resistant a few weeks after their recovery. According to Frédéric Tangyn from the Paris research center Institut Pasteur, the study says nothing about the period of immunity – because it only lasted one month.
However, many experts are skeptical about the reports from Asia that corona patients contracted a second infection. They think it is rather unlikely that it is actually a new infection.
Bad symptoms despite antibodies
According to Balloux, the virus could become chronic in some people, such as the herpes pathogen. Or the negative test results were flawed, and in reality the patients never got rid of the virus: “This would indicate that people remain contagious for a long time, several weeks,” he says. “That would not be ideal.”
A study published in early April with 175 cured Shanghai patients showed that most of them had developed different concentrations of Covid-19 antibodies between ten and 15 days after the onset of the lung disease caused by the virus. But whether “the presence of antibodies can be equated with immunity alone is another question,” warns the US expert at the WHO, Maria Van Kerkhove.
“We are wondering if someone who had Covid-19 is really that much protected,” says virologist Jean-François Delfraissy, who advises the French government. Even worse: According to Pasteur researcher Tangy, the antibodies could even aggravate the disease. He points out that the worst symptoms of Covid 19 do not appear until a patient has already developed antibodies.
It is also unclear who develops more effective antibodies – the most or the least affected patients, the older or the young? Given all of these uncertainties, some experts are also questioning the success of herd immunity. For Australian epidemiologist Archie Clements, only one thing is certain: “The only real solution is a vaccine.”
– .
