“For example, the initial booster shot reduced hospital admissions by 81% in the first month after it was administered,” said Mbinta, of Victoria University’s School of Health.
After six months, that effectiveness fell to around 57%.
“Similarly, the second booster reduced hospitalisations by 81.8% in the first month – by month six, this figure had dropped to 49%.”
The drop in stopping infection was sharper still, going from 57% at the one-month mark, to about 10% after six months.
Importantly, however, the drop in preventing death from Covid-19 was small: the first booster was shown to be about 93% effective at doing so for two months – and five or six months later, that protection had only fallen to about 87.2%.
“Our findings suggest vaccination provides longer-term protection against hospitalisation and dying from Covid-19, and shorter-term protection against infection,” study co-author Professor Colin Simpson said.
Simpson added that more research would be needed to assess vaccine effectiveness beyond the six-month periods they analysed, and also that of future doses.
The study comes as figures show most of the under-65 population eligible for free second boosters – including around eight in 10 people in their 30s and 40s – haven’t bothered to get one.
Fortunately, uptake was much higher among our over-65s, of whom nearly three-quarters have received the second booster – and who continued to make up the bulk of Covid-attributed hospitalisations and deaths.
Experts say boosting remains especially important for older Kiwis and other at-risk groups like immuno-compromised people, as the antibody top-ups they get from the vaccine wanes markedly faster.
Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.
New data: How much protection is the Covid vaccine giving Kiwis?
