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A recent study by the Liverpool School of Tropical Medicine estimates that herd immunity for COVID-19 may occur at lower levels than previously assumed

Proportion of population at which herd immunity is reached

Percent

Coefficient of variation**

Susceptibility. R = 3.0--Susceptibility. uncontrolled outbreak

Connectivity, R = 3.0--Connectivity. uncontrolled outbreak

•    It is a well known fact within epidemiology that higher variation in people's susceptibility to the virus or their level of connectivity to other people reduces the level at which “herd immunity” is achieved

•    This is because people who are most likely to get the virus - either because they are highly susceptible or have very high levels of interaction with other people - tend to do so before others, and subsequently, if they gain immunity, act as a brake on the virus’s spread

•    Historically, highly computationally intensive spatial models were used to estimate this. However, these are difficult to construct when a virus is not well understood, and have been used rarely for COVID-19

•    Through changing the methodology of an SEIR model¹, a team from the Liverpool School of Tropical Medicine estimated this relationship for COVID-19, and indicated that if the earliest estimates of variation for COVID-19 are correct, herd immunity could occur at lower levels than previously assumed

O 2020 L E K. Consulting LLC

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   Nonetheless, current estimates suggest that all countries remain a long way from even these lower levels of infection, so it is morę likely to be reached slowly over time, rather than as a direct policy objective, and further studies of the virus will be required to corroborate and refine these estimates