A vaccinologist says she will not be rushing to get her fourth immunisation against Covid-19.

Adults in Australia can now get Moderna's Omicron Covid-19 booster vaccine.

University of Auckland vaccinologist Helen Petousis-Harris told Morning Report there was some benefit to it for the "old and frail" and immunocompromised, but most people would have enough immunity from previous infection and three Covid vaccines.

She says new vaccines may become available by next winter.

"It's coming, but ... it's not a matter of urgency."

Petousis-Harris says the population in New Zealand had immunity.

"The recipe for the best immunity that we have at the moment is having had your vaccine and then had the Omicron infection and that is the most superior immunity.

"If you've got that hybrid immunity, I wouldn't be running out to get myself boosted. I don't think it would be particularly useful."

She says had not seen any evidence to suggest a fourth vaccine would help further.

Recent data suggests the main Omicron subvariant in New Zealand is becoming less dominant as new subvariants rise.

The latest Covid report from the Ministry of Health says that BA.5, which drove the recent winter wave now accounted for about 75 percent of cases in the two weeks to 30 September. That was the variant's lowest share of cases in months.

The BA.4.6 variant's share increased sharply in the latest data to 15 percent, while the BA.2.75 variant was also gaining and was up to 10 percent.

The ministry's report also says the Omicron BQ.1.1 lineage had not been detected in New Zealand in the fortnight to 30 September.

Earlier this year, the government confirmed people would be able to get their second booster dose six months after their first.

This fourth dose covers several hundred thousand people in vulnerable groups, including elderly, aged care residents, and those in disability care facilities.

Asked it the country would benefit from making a second booster more widely available, Immunisation Advisory Centre medical director Dr Nikki Turner says: "No".

- RNZ.