A research paper published in BMC infectious diseases on 11th March reviewed this issue.  

It is essential to understand the epidemiological parameters that determine the transmission dynamics of COVID-19 for public health intervention.

Globally, a number of studies have been conducted to estimate the average serial interval and incubation period for COVID-19.  

Combining findings of existing studies that estimate the average serial interval and incubation period of COVID-19 significantly improves the quality of evidence. 

The researchers aimed to determine the overall average serial interval and incubation period for COVID-19.  

They carried out a comprehensive search strategy from international electronic databases between 1st June and 31st July 2020.  They included all observational studies which reported the serial interval or incubation period in persons diagnosed with COVID-19. 

They combined a total of 23 studies to estimate the overall mean serial interval of COVID-19.  They also pooled the mean incubation period of COVID-19. 

They found that the onset of COVID-19 symptoms in an index case and the onset of symptoms in a secondary case was 5.2 days.  This is the so called the serial interval, so this is the onset of COVID symptoms in the initial case and the onset of COVID symptoms in the secondary case.  

They also found that the average time from infection until symptom onset, the incubation period, was 6.5 days. 

This study confirmed that the average serial interval of COVID-19 is shorter than the average incubation period. 

This therefore suggests that a substantial number of COVID-19 cases are attributed to pre-symptomatic transmission.  

The London General Practice encourages Covid testing of the workforce and effective vaccination in order to reduce the transmission of SARS-CoV-2.

Dr Paul Ettlinger
BM, DRCOG, FRCGP, FRIPH, DOccMed

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