BEIJING– Chinese researchers have revealed that the asymptomatic infections of the novel coronavirus disease (Covid-19) have a weaker immune response compared with the symptomatic ones. A research team from the Chongqing Medical University studied 37 asymptomatic cases, aging from eight to 75 years old, who were admitted to the Wanzhou Peoples Hospital, southwest Chinas Chongqing Municipality, for quarantine. The team found that the median viral shedding duration, defined as the interval from the first to last positive nasopharyngeal swab, among the asymptomatic cases was 19 days, longer than 14 days among patients with mild symptoms out of the 37 symptomatic people who were chosen as the control group, according to the research results published in the journal Nature Medicine. Both in the acute phase (the period when the viral RNA can be found in a respiratory specimen) and the early convalescent phase (eight weeks after being discharged from the hospital), the levels of IgG, an antibody specific to Covid-19, among the asymptomatic cases were significantly lower relative to the symptomatic cases. In addition, 30 asymptomatic cases had a decrease in neutralizing antibody levels in the early convalescent phase, whereas the decrease was observed only in 23 symptomatic cases. The research results indicated that the asymptomatic cases, compared with the symptomatic ones, had a weaker immune response to Covid-19. The discovery of the reduction in IgG and neutralizing antibody levels in the early convalescent phase may contribute to the immunity strategies and serological surveys, said the team.
