Among the pernicious features of Covid-19, the incubation period is longer than many other viral respiratory infections, including influenza, respiratory syncytial virus and rhinovirus. The good news is that the time between exposure and the onset of symptoms appears to be decreasing. Scientists from Peking University and Tsinghua University in Beijing analyzed data from more than 140 studies to estimate the incubation period of Covid caused by different strains of SARS-CoV-2. It dropped from an average of five days with alpha infection to 3.42 days with omicron, according to a study published Monday in the journal JAMA Network Open. The researchers also noted variable incubation periods in different age groups and disease severity. “The findings of this study suggest that SARS-CoV-2 is continuously evolving and mutating throughout the Covid-19 pandemic, generating variants with different enhanced transmission and virulence,” Wannian Liang and colleagues said. “Determining the incubation period of different variants is a key factor in determining the period of isolation.” The findings are important for places like China and Hong Kong, which maintain a Covid Zero policy aimed at eradicating any signs of the virus as soon as possible. All those infected and all foreign travelers are expected to self-isolate during the potential incubation period to prevent transmission to others. Both China and Hong Kong have recently reduced quarantine periods for new arrivals as part of their efforts to revive their economies.
