Contact-adjusted Immunity Levels against SARS-CoV-2 in Korea and Prospects for Achieving Herd Immunity

Abstract

The proportion of population vaccinated cannot be directly translated into the herd immunity. We have to account for the age-stratified contact patterns to calculate the population immunity level, since not every individual gathers evenly. Here, we calculated the contact-adjusted population immunity against severe acute respiratory syndrome coronavirus 2 in South Korea using age-specific incidence and vaccine uptake rate. We further explored options to achieve the theoretical herd immunity with age-varying immunity scenarios. As of June 21, 2021, when a quarter of the population received at least one dose of a coronavirus disease 2019 (COVID-19) vaccine, the contact-adjusted immunity level was 12.5% under the social distancing level 1. When 80% of individuals aged 10 years and over gained immunity, we could achieve a 58.2% contact-adjusted immunity level. The pros and cons of vaccinating children should be weighed since the risks of COVID-19 for the young are less than the elderly, and the long-term safety of vaccines is still obscure.

Presumed population immunity to SARS-CoV-2 in South Korea, April 2022

“…The contact mixing pattern between different age groups widely varies across countries and settings [ 1 ]. In Korea, the contact number in school-aged children was found to be this age group had the highest contact number of all [ 9 ], suggesting that the improved population immunity in this age group may have substantially reduced the community transmission of SARS-CoV-2.…”