Research press release


Nature Medicine

Immunology: COVID-19 vaccination helps protect unvaccinated people

重症急性呼吸器症候群コロナウイルス2(SARS-CoV-2)ワクチンの接種レベルが高いほど、16歳以下でワクチン接種を受けていない人たちのSARS-CoV-2感染率が低くなることを示した研究がNature Medicine に掲載される。この知見は、イスラエルの別々の177の地域で2020年12月6日から2021年3月9日にかけて行われたワクチン接種の記録と感染検査結果の分析に基づくもので、SARS-CoV-2ワクチンの接種がワクチン既接種者とワクチン未接種者の両方を感染から守ることを明らかにしている。


イスラエルでは、2020年12月19日にワクチン接種が始まり、9週間以内に人口のほぼ50%が初回接種を終えた。ワクチン接種が、ワクチン未接種者の間でのSARS-CoV-2伝播を集団レベルで減少させるかどうかを調べるために、R Kishony、T Patalonたちは、ワクチン接種率が異なっている177の地域(ファイザー・ビオンテック社製ワクチンの初回接種を受けた人数は合計で137万人になる)と、接種できるワクチンがまだないために接種を受けていない16歳以下の集団に着目した。そして、一定の期間をおいてそれぞれの地域でSARS-CoV-2検査を行い、陽性者数の変化を調べた。その結果、ある集団内のワクチン既接種者数が20%増えるごとに、同じ地域のワクチン未接種集団中でSARS-CoV-2検査で陽性と判定される数が、平均して約2分の1に減少することが分かった。


Higher levels of vaccination against COVID-19 were associated with lower rates of infection with SARS-CoV-2 among a group of unvaccinated people of 16 years of age and under, reports a study in Nature Medicine. The findings, based on an analysis of vaccination records and test results from 177 geographically distinct communities in Israel from 6 December 2020 to 9 March 2021, demonstrate that vaccination against COVID-19 helps to protect those who have and have not been vaccinated.

Clinical trials and vaccination campaigns have shown that the Pfizer–BioNTech vaccine against COVID-19 is highly effective at preventing infection and disease at the individual and community levels. However, it has been suggested that vaccination could also increase transmission due to changes in human behavior. For example, those who have been vaccinated might be less mindful of social distancing or may not quarantine after coming into contact with a person with COVID-19.

The vaccination rollout in Israel began on 19 December 2020 and administered the first dose of the vaccine to almost 50% of the population within 9 weeks. To determine whether vaccination reduces the transmission of SARS-CoV-2 among unvaccinated people at the population level, Roy Kishony, Tal Patalon and colleagues focused their attention on 177 geographically distinct communities, which had varying vaccination rates (amounting to a total of 1.37 million first-dose recipients of the Pfizer-BioNTech vaccine), and a cohort of unvaccinated people under 16 years of age for whom the vaccine was not yet available. The authors assessed changes in the number of positive tests for COVID-19 within each community between fixed time intervals. They found that, on average, for each 20% increase in the number of vaccinated people in a given population, the number of positive SARS-CoV-2 tests in the unvaccinated population in the same community decreased approximately two fold.

The authors caution that their findings do not take into account the possibility of naturally acquired immunity to SARS-CoV-2. They conclude that, although the observed vaccine-associated protection of the unvaccinated population is encouraging, further studies are needed to understand whether and how vaccination campaigns might support the prospect of herd immunity and disease eradication.

doi: 10.1038/s41591-021-01407-5


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