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Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections

The clinical features and immune responses of asymptomatic individuals infected with severe acute respiratory syndrome coronavirus 2 ( SARS-CoV-2 ) have not been well described.

Researchers have studied 37 asymptomatic individuals in the Wanzhou District who were diagnosed with RT–PCR-confirmed SARS-CoV-2 infections but without any relevant clinical symptoms in the preceding 14 days and during hospitalization.
Asymptomatic individuals were admitted to the government-designated Wanzhou People’s Hospital for centralized isolation in accordance with policy.

The median duration of viral shedding in the asymptomatic group was 19 days ( interquartile range [ IQR ], 15–26 days ).

The asymptomatic group had a significantly longer duration of viral shedding than the symptomatic group ( log-rank P = 0.028 ).

The virus-specific IgG levels in the asymptomatic group ( median S/CO, 3.4; IQR, 1.6–10.7 ) were significantly lower ( P = 0.005 ) relative to the symptomatic group ( median S/CO, 20.5; IQR, 5.8–38.2 ) in the acute phase.

Of asymptomatic individuals, 93.3% ( 28/30 ) and 81.1% ( 30/37 ) had reduction in IgG and neutralizing antibody levels, respectively, during the early convalescent phase, as compared to 96.8% ( 30/31 ) and 62.2% ( 23/37 ) of symptomatic patients.

Forty percent of asymptomatic individuals became seronegative and 12.9% of the symptomatic group became negative for IgG in the early convalescent phase.
In addition, asymptomatic individuals exhibited lower levels of 18 pro- and anti-inflammatory cytokines.

These data suggest that asymptomatic individuals had a weaker immune response to SARS-CoV-2 infection.
The reduction in IgG and neutralizing antibody levels in the early convalescent phase might have implications for immunity strategy and serological surveys. ( Xagena )

Long Q et al, Nat Med 2020; 26: 1200–1204