New research analyzing health data for more than five million Kiwi residents shows COVID-19 vaccinations have been most effective at preventing infections and hospital admissions in the first month after they're administered. The study is published in the New Zealand Medical Journal . "By six months, vaccine effectiveness drops significantly, highlighting the important role of booster shots in maintaining protection against COVID-19," said study co-author Professor Colin Simpson, an associate dean at the University's Faculty of Health.
The study's findings are based on comparing health outcomes for vaccinated and unvaccinated people for the period from 8 December 2020 to 28 February 2023 when the omicron variant of COVID-19 was dominant. The researchers assessed the effectiveness of the first and second vaccine doses , plus the subsequent two boosters, in preventing infection, hospitalizations, and death from COVID-19. Health data for 5.
3 million people were included in the study. Of those: Analysis of health data showed vaccine effectiveness in preventing infection and hospital admissions from COVID-19 was the highest in the first 30 days after vaccination, said co-author Dr. James Mbinta, a research fellow in the School of Health.
"For example, the initial booster shot reduced hospital admissions by 81% in the first month after it was administered. By month six, its effectiveness had declined to 57.4%.
"Similarly, the second booster reduced hospitalizations by 81.8% in the .