Popularization of research advances on COVID-19

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Our antibodies protect us for at least 5 months

Since the beginning of the epidemic, there have been numerous questions raised concerning antibody responses against SARS-CoV-2. What levels of antibodies are necessary to give protection against reinfection, and how long will such protection last? Although we have assembled a great deal of data relating to critical cases of COVID-19, we don’t know as much about moderate or asymptomatic cases;  they have been less analyzed although they represent the majority of infections.

From March to October 2020, researchers at the Mount Sinai Hospital in New York studied the quantities of anti-S antibodies in 72 401 patients who had been found to be positive by RT-PCR, or by a doctor’s diagnosis, or who had declared as having been in contact with infected individuals. Amongst the people studied, less than 5% required hospitalization. The aim was to use volunteers who were convalescing to treat critically ill patients by adoptive transfer of their serum (blood cleared of cells and platelets) containing anti- SARS-CoV-2 antibodies.

Using an efficient “in-house” ELISA test to evaluate levels of anti- SARS-CoV-2 antibodies, it was found that of 30 082 patients who were positive :

  • 7,12% had low levels of antibodies;
  • 22,49% had moderate levels;
  • 70,39% had high levels.

Since not all of these antibodies were neutralizing, an in vitro test was also used, showing that in patients with moderate or high levels of antibodies, 90 to 100% had developed neutralizing antibodies. 121 donors were recalled for 2 supplementary evaluations: their levels of antibodies remained stable for 82 days after the appearance of symptoms and reduced slightly after 148 days.

As had already been observed during the SARS-CoV-1 (2002) and MERS-CoV (2012) epidemics, this study indicated that the vast majority (92,88% in this instance) of COVID-19 patients have adequate levels of neutralizing antibodies over 5 months.

However, this group of patients is still under observation. Not all of them had been tested by RT-PCR, but other studies have shown that 95 to 99% of patients diagnosed as positive by RT-PCR also showed positive with the ELISA test. Patients who do not develop these antibodies are therefore in the minority.

No clinical testing has yet formally shown that infection by SARS-CoV-2 would give protection against a second infection by the same virus. But this study’s researchers are optimistic: in the case of infection by other coronaviruses, the neutralizing antibodies confer protection for several years, and, in case of reinfection, symptoms are reduced. Moreover, in primates, after natural infection with SARS-CoV-2, adoptive antibody transfer, or even a vaccine, provide effective protection against reinfection.

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