The biggest benefits of Covid vaccines appear to be in the first six months

A new study of more than five million Kiwis, published in today's New Zealand Medical Journal, has found vaccines and boosters were most effective within the first few months after injection.

The second booster's effectiveness against hospitalisation dropped from 82 percent to 49-percent at six months.

Defence against infection fell from 57 percent to 10-percent.

The researchers recommend future studies to understand changes beyond six months, and differences by vaccine type and variant.