Estimating unobserved SARS-CoV-2 infections in the United States

Alex Perkins; Sean M. Cavany; Sean M Moore; Rachel J Oidtman; Anita Lerch; Marya Poterek

By March 12, there were a total of 152 reported cases and one reported death in the US that were classified as imported on the basis of international travel to areas with known SARS-CoV-2 transmission (19) . By jointly estimating ρ travel and the relative infectiousness of asymptomatic infections, α, we obtained a median estimate of 0.39 (95% PPI: 0.15 -0.90) for ρ travel under our baseline scenario. This resulted in a median of 452 (95% PPI: 206 -1068) imported infections. Under the alternative importation timing scenario, where importation timing was based on international case reports, we obtained a median estimate of 1.00 (95% PPI: 0.98 -1.00) for ρ travel and 187 (95% PPI: 174 -202) imported infections. An estimate of ρ travel = 1.00 implies that all symptomatic imported infections were detected, but it still means that asymptomatic infections would have been undetected. Whereas the baseline importation scenario resulted in most importations happening in March and a few throughout February and January, the alternative importation scenario resulted in many importations still happening in March but a large proportion of them also happening around late January (Fig. S3) .