COVID-19 was twice as contagious during the early months than WHO estimates

Branco Weiss Fellow Gabriele Manoli is co-author of a research article recently published in PLOS One that analyzes the spread of the COVID-19 pandemic in its early stages. The analysis shows that governments had a much smaller window of time to act than previously thought: During the early months of the pandemic, the average number of new infections caused by an infected individual (i.e. the basic reproduction number, R0) was 4.5, or more than twice as many as the initial 2.2 rate estimated by the World Health Organization at the time.

This means that governments had just 20 days from the first reported cases to implement non-pharmaceutical interventions stringent enough to reduce the transmission rate to below 1.1 and prevent widespread infections and deaths. If delays in implementing these interventions allowed the reproduction rate to remain above 2.7 for at least 44 days – as was the case in many of the 57 countries studied – any subsequent interventions were unlikely to be effective.

The new analysis helps identify the timing and type of interventions that may work best, the hospital capacity needed, as well as other critical considerations. In addition, the researchers estimate that it requires 78% of a population to no longer be susceptible to COVID-19 to reach herd immunity. That can help inform decisions about how many vaccines are needed.

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