As severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the novel coronavirus that causes coronavirus disease 2019 (COVID-19), began to spread globally, it became apparent that the virus, unlike the closely related SARS-CoV in the 2003 outbreak, could not be contained by symptom-based screening alone. Asymptomatic and clinically mild infections were uncommon during the 2003 SARS-CoV outbreak and there were no reported instances of transmission from persons before the onset of symptoms. SARS-CoV-2 spread faster than SARS-CoV and accumulating evidence showed that SARS-CoV-2, unlike SARS-CoV, can be transmitted from persons without symptoms.
Measures to reduce transmission from individuals who do not have COVID-19 symptoms have become controversial and politicized and have likely had negative effects on the economy and many societal activities. Transmission by persons who are infected but do not have any symptoms can arise from 2 different infection states: presymptomatic individuals (who are infectious before developing symptoms), and individuals who never experience symptoms (asymptomatic infections).
The baseline assumptions in a study published in JAMA were that peak infectiousness occurred at the median of symptom onset and that 30% of individuals with infection never develop symptoms and are 75% as infectious as those who do develop symptoms. The assumptions imply that persons with infection who never develop symptoms may account for approximately 24% of all transmission. Measures such as wearing masks, hand hygiene, social distancing, and strategic testing are foundational to slowing the spread of COVID-19 until safe and effective vaccines are widely available and used.
Stay the course, get vaccinated, mask up, and stay tuned!