Nature Medicine: COVID-19 vaccination protects unvaccinated populations

Currently, mass vaccination of COVID-19 vaccine is being carried out around the world. Multiple clinical trials and real-world studies have shown that the COVID-19 vaccine provides effective protection against COVID-19 in recipients. The other goal of mass vaccination is "herd immunity," which means that when a sufficient percentage of the population becomes immune from the vaccine (or natural infection), they prevent the spread of the virus so that the unvaccinated population does not become infected.

Then, in the novel coronavirus is still spreading in many countries and regions in the world today, can we achieve "herd immunity" by vaccinating the new coronavirus vaccine? A study conducted in Israel and published today in Nature Medicine shows that the vaccination of the novel coronavirus vaccine not only protects those who receive it, but also reduces the risk of infection in unvaccinated people.

Israel has one of the highest rates of COVID-19 vaccination in the world, with more than 60% of the Israeli population receiving at least one dose of COVID-19 vaccination, according to Our Word in Data. Real-world studies conducted in the country have also revealed excellent results in protecting those vaccinated with the new coronavirus.

In this study, we analyzed whether the novel coronavirus vaccine can reduce the risk of novel coronavirus infection in unvaccinated individuals at the population level. The researchers analyzed 177 geographically located communities with different vaccination rates. They analyzed data on two groups of people who had been vaccinated and tested positive for nucleic acid, which indicates infection with novel coronavirus.

One category is adults aged 16-50 years, who have been receiving COVID-19 vaccine at increasing rates since mid-December 2020. The other group is adolescents and children under 16 years of age, who do not have an authorized vaccine available and therefore have not been vaccinated against COVID-19.

The researchers measured changes in vaccination rates among adults aged 16 to 50 in different communities at fixed intervals, and then measured changes in positive nucleic acid tests among people younger than 16 in the same community after 28 days. The design gives time for the vaccine to take effect and gives vaccinated adults a chance to interact with the unvaccinated population, allowing researchers to observe the vaccine's protective effect on the unvaccinated population.

The results showed a strong negative correlation between an increase in the percentage of vaccinated adults aged 16-50 years and the positive nucleic acid test rate among unvaccinated people under 16 years of age in the same community. The higher the proportion of vaccinated, the lower the positive rate of nucleic acid detection in the unvaccinated population. On average, for every 20 percent increase in the percentage of vaccinated people in a community, the number of positive nucleic acid tests among unvaccinated people in the same community dropped by two times.