How much do asymptomatic infections contribute to an epidemic?

What is it about?

Many infectious diseases in humans may manifest with no or mild symptoms. Yet, infected individuals with no symptoms still participate in spreading the disease. During the full course of an epidemic, estimating how many transmissions were caused by asymptomatic individuals is not straightforward. For example, if 60% of infected individuals are asymptomatic, they are not necessarily responsible for 30% of all transmissions when their infectiousness is on average half that of symptomatic cases. This paper provides a simple formula to estimate the contribution of asymptomatic infections to the total number of transmissions during an epidemic.

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Why is it important?

Asymptomatic cases are difficult to detect. Hence, reaching them for control measures requires more efforts. Quantifying their importance in spreading the disease enable public health measures to be appropriately targeted and scaled.