People who have been infected by the new coronavirus do not develop symptoms of the disease Covid-19, may have lower antibody levels against the virus than those who are more seriously ill, suggest that the chinese scientists Thursday in the journal Nature Medicine.
The researchers warn, as a result, risks to set up “passports of immunity” which would be expected to ensure that their holders are protected against the disease.
A study on 37 individuals
The study describes the immunological and clinical, the cases of 37 people without symptoms whose infection has been diagnosed by a virologic test (RT-PCR nasopharyngeal swab) in the district of Wanzhou (in Chongqing municipality, southwest China) by the 10th of April 2020.
Among these 37 patients, asymptomatic – identified in a group of 178 people with the infection with the novel coronavirus, the SARS-CoV, 22 were women and 15 men, aged from 8 to 75 years. The median age was 41 years.
Excretion viral over a longer period
The authors Have Long Hua of the medical University of Chongqing and his colleagues, have found that these patients put in isolation in hospital had a median duration of viral excretion of 19 days compared to 14 days in 37 patients with symptoms (fever, cough, shortness of breath…). The duration of excretion is not equivalent, however, an infectivity which remains to be assessed, are the responsibility of the authors.
Eight weeks after leaving the hospital, the levels of neutralizing antibodies, which confer a priori immunity against the virus, had decreased in 81.1% of patients without symptoms, compared to 62,2 % in symptomatic patients.
The inflammatory response reduced
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 an inflammatory response reduced.
“In this study, we observed that the rate of IgG and neutralizing antibodies in a high proportion of people who have recovered from an infection with SARS-CoV-2 begin to decrease within 2 to 3 months after infection,” they write.
Immunity probably more brief
These data, together with previous analyses of neutralizing antibodies, highlight the potential risks of the use of “passports of immunity” and plead in favour of public health interventions (social distancing, hygiene, isolation of high-risk groups, screening for generalized), according to the authors.
They advocate for further research “urgently” on larger groups of patients with and without symptoms to determine the duration of immunity from antibodies.
In spite of the small number of patients, “this corresponds to some of the concerns according to which the natural immunity to the coronavirus may be short-lived,” according to the professor of immunology british Danny Altmann, who was not involved in this study.