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 

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