COVID-19: presymptomatic, asymptomatic transmission in ~50% of cases, per modeling

  • 08/01/2021

  • Liz Scherer
  • Clinical Essentials
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Takeaway

  • People infected with SARS-CoV-2 but without symptoms may be involved in ≥50% of transmission, according to this modeling study. 
  • Identification and isolation confined to people who are symptomatic with COVID-19 will not control transmission. 

Why this matters

  • In addition to mask wearing and social distancing, asymptomatic testing is important among those with possible exposure and/or high risk for exposure to infected persons within households or the community.

Key results

  • Under a variety of baseline assumptions (average relative hourly infectiousness, median incubation periods), ~59% of transmissions occurred from persons without symptoms: 35% were presymptomatic, and 24% were asymptomatic.
  • With peak infectiousness ranging from 2 days before (more presymptomatic transmission) vs 2 days after (less presymptomatic transmission) median symptom onset, and assuming an asymptomatic transmission range of 0%-70%, at least 50% of new SARS-CoV-2 infections arise from pre/asymptomatic transmission.
  • On the conservative end of peak infectiousness 2 days postmedian onset with 0% asymptomatic transmission, persons without symptoms would account for >25% of transmissions.

Study design

  • Decision analytical modeling study evaluating the proportion of SARS-CoV-2 community transmission attributable to persons without symptoms (i.e., presymptomatic, asymptomatic).
  • Funding: CDC.

Limitations

  • Qualitative precision lacking.
  • Proportion of presymptomatic and never-symptomatic infections is unknown. 
  • Individual levels of infectiousness likely underestimated.