No symptoms of Covid-19 can mean weaker immunity, study finds
People infected with the new coronavirus who did not develop symptoms of the disease may have a weaker immune response against the virus than those who did fall sicker, Chinese researchers suggest in the journal Nature Medicine.
The researchers warn, therefore, about the risks of implementing "immunity passports" that would guarantee their holders to be protected against the virus.
The study describes in the immunological and clinical plan in the case of 37 people without symptoms whose infection was diagnosed by a nasopharyngeal virological test in the Wanzhou district, southwest China) before April 10, 2020.
Among those 37 asymptomatic patients identified in a group of 178 people infected with the new coronavirus, 22 were women and 15 men, aged 8 to 75 years (mean age: 41 years).
The authors, Ai-Long Hua, from Chongqing Medical University and their colleagues, found that these patients, isolated in hospital, had an average duration of viral excretion of 19 days, compared to 14 days in 37 patients who presented symptoms (fever, cough, breathing difficulties).
This duration of excretion does not mean, however, that they infect others, which remains to be evaluated, the authors reveal.
Eight weeks after hospital discharge, levels of neutralizing antibodies, which a priori give immunity to the virus, decreased 81.1% in patients without symptoms, compared to 62.2% in patients with symptoms.
To further explain the immune response, the researchers measured some substances (cytokines and chemokines) in the blood and observed their low levels in asymptomatic patients, showing a reduced anti-inflammatory response.
These data, as well as previous analyzes of neutralizing antibodies, highlight the potential risks of using “immunity passports”, and therefore advocate the continued application of common preventive health measures.