Herd immunity can defeat COVID-19

Herd immunity that prevents the spread of the coronavirus can be developed with 43% coverage of COVID-19 patient or a vaccinated population, Report says, citing Science.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread globally despite the many different preventive measures that have been put in place to reduce transmission. Some countries aimed for suppression by extreme quarantine measures (lockdown), and others for mitigation by slowing the spread using specific preventive measures in combination with protection of the vulnerable a critical question for both policies have been when to lift some or all the restrictions. A closely related issue is if and when herd immunity can be achieved. Herd immunity is defined as a level of population immunity such that disease spreading will decline and stop even after all preventive measures have been relaxed. If all precautionary measures are relaxed when the immunity level from infection is below the herd immunity level, then the second wave of the disease may start once restrictions are lifted.

Despite various levels of preventive measures, in 2020, many countries have suffered severely from the coronavirus 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome. We show that population heterogeneity can significantly impact disease-induced immunity as the proportion infected in groups with the highest contact rates is more significant than in groups with low contact rates. We estimate that if R0 = 2.5 in an age-structured community with mixing rates fitted to social activity, then the disease-induced herd immunity level can be around 43%, which is substantially less than the classical herd immunity level of 60% obtained through homogeneous immunization of the population. Our estimates should be interpreted as an illustration of how population heterogeneity affects herd immunity, rather than an exact value or even the best forecast.