An interesting article published in the Journal of the American Medical Association looked at this important subject. SARS-CoV-2 is readily transmitted person to person. Optimal control of COVID-19 depends on direct resources and health messaging to mitigation efforts that are most likely to prevent transmission, but the relative importance of these measures is in doubt. This study tried to assess the proportion of SARS-CoV
2 transmissions in the community that are likely to occur from persons without symptoms.
The baseline assumptions for the model with a peak infectiousness occurred at the medium of symptom onset and that 30% of individuals with infection who never develop symptoms are 75% as infectious as those who do develop symptoms.
Combined, these baseline assumptions imply that persons with infection who never developed symptoms may account for about 24% of all transmissions.
In this base case, 59% of all transmissions came from asymptomatic transmission, comparing 35% from presymptomatic individuals and 24% from individuals who never develop symptoms. Under a broad range of values for each of these assumptions, at least 50% of new SARS-CoV-2 infections were estimated to have originated from exposures to individuals with infection but without symptoms.
Transmission from asymptomatic individuals is thus estimated to account for more than half of all transmissions. Therefore, in addition to identification AND isolation of persons with symptomatic COVID-19, effective control of spread will require reducing the risk of transmission from people with infection who do not have symptoms. These findings therefore suggest measures such as wearing masks, hand hygiene, social distancing and strategic testing of people who are not ill will be fundamental to slowing the spread of COVID-19 until the safe and effective vaccines have been adequately administered. This would appear to suggest that the current lockdown may be the only way of preventing transmission.
The London General Practice supports all measures which are able to reduce the transmission of this deadly virus and hence reduce morbidity and mortality.
Dr Paul Ettlinger
BM, DRCOG, MRCGP, FRIPH, DOccMed