People who have been infected with coronavirus, without developing symptoms of Covid-19 disease, may have a weaker immune response to the virus than those who have become more seriously ill, Chinese researchers suggest in the journal Thursday Nature Medicine. The researchers warn, therefore, of the risks of instituting "immunity passports" which are supposed to ensure that their holders are protected against the disease.
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Longer duration of viral shedding in asymptomatic patients
The study describes immunologically and clinically, the case of 37 symptomless people whose infection was diagnosed by a virological test (RT-PCR by nasopharyngeal sampling) in the district of Wanzhou (in the municipality of Chongqing , southwest of China), before April 10, 2020.
Among these 37 asymptomatic patients - identified in a group of 178 people infected with the infection due to the new coronavirus, SARS-CoV, 22 were women and 15 men, aged 8 to 75 years (median age: 41 years) ).
The authors, Ai-Long Hua of Chongqing Medical University and his colleagues, found that these patients, placed in hospital isolation, had a median duration of viral excretion of 19 days, compared with 14 days in 37 patients showing symptoms (fever, cough, shortness of breath ...). This duration of excretion, however, does not amount to infectivity, which remains to be assessed, note the authors.
Eight weeks after discharge from the hospital, the levels of neutralizing antibodies, which a priori confer immunity against the virus, had decreased in 81.1% of patients without symptoms, compared with 62.2% in symptomatic patients.
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Determine the duration of immunity from antibodies
To further elucidate the immune response, the researchers measured certain substances (cytokines and chemokines) in the blood and observed their low levels in asymptomatic patients, showing a reduced inflammatory response.
"In this study, we observed that the levels of IgG and neutralizing antibodies in a high proportion of people who have recovered from SARS-CoV-2 infection begin to decrease within 2 to 3 months. infection, "they write.
These data, as well as previous analyzes of neutralizing antibodies, highlight the potential risks of using "immunity passports" and plead in favor of public health interventions (social distancing, hygiene, isolation of high-risk groups, generalized screening), according to the authors.
They advocate continuing research "urgently" on larger groups of patients with and without symptoms to determine the duration of immunity from antibodies.
Despite the small number of patients, "this corresponds to some concerns that natural immunity to coronaviruses may be short lived," according to British immunology professor Danny Altmann, who was not involved in this study.