A study from the University of Oxford has warned that the Pfizer Covid-19 vaccine becomes significantly less effective against the Delta variant just four months after the second dose - although it still offers some protection.
The study, published last week, makes the case for administering booster shots of the vaccine to keep efficacy high.
It found the efficacy of the Pfizer vaccine against symptomatic infection falls significantly within 90 days of receiving a second dose to about 75 per cent against the Delta variant.
This is down from 85 per cent effectiveness within the first fortnight of the second dose.
It also showed that the Pfizer vaccine is initially more effective than the AstraZeneca vaccine. However, about four months after the second dose, the Pfizer jab's efficacy wanes to the point where AstraZeneca's vaccine become the more effective of the two.
Director general of health Dr Ashley Bloomfield said he was aware of the studies showing waning efficacy.
"The studies about waning immunity are still in their early days, it's really a watch and wait at the moment," Bloomfield said.
"The numbers are quite small but that's something we're keeping an eye on," Bloomfield said.
Other countries are beginning to offer or recommend booster shots of the Covid vaccines. Israel is offering some boosters and the United States will begin offering people a third shot after September 20.
The studies could be of some concern to the first people vaccinated in New Zealand, mainly border workers, who will soon approach the period where the studies suggest efficacy wanes.
Bloomfield said these people should not be concerned.
"There's no evidence efficacy is waning now - we started vaccinating in February and there's nothing to suggest that given hundreds of millions of these doses have been given around the world that there is waning immunity
Nevertheless, Bloomfield said the Government was in "active talks" with Pfizer about securing booster shots which will either be an additional dose of the existing vaccine or a new, "tweaked" version.
"We are in active talks with Pfizer about ensuring we're going to get access to a booster shot of the Pfizer vaccine either similar to the one now or if it needs to get tweaked to a new sort of version of it," Bloomfield said.
National's Covid-19 spokesman Chris Bishop said the Government should have already ordered booster shots.
"We should already have ordered the boosters - other countries are well ahead of us on this, just as they were ahead of us ordering the Pfizer vaccine," Bishop said.
He said the Government should start by ordering additional doses of the original Pfizer vaccine for use as boosters.
Bishop said if the Pfizer vaccine was outdated by new "tweaked" boosters coming online, the Government could donate leftover Pfizer jabs and order the most up to date jab.
"We can always give away the vaccines if we decide we don't need them," Bishop said.
"This is the best investment a government can make in New Zealanders' health but also in the New Zealand economy," Bishop said.
Covid-19 Minister Chris Hipkins said the border workforce could be vaccinated from any jabs left over from the 10 million Pfizer vaccine doses the Government has already ordered. These are set to arrive throughout the year.
"We already have additional shots available should we need to use them for booster shots
"We've got over 10 million doses coming between now and the end of the year. We know we will need about 8.2 million of those to fully deliver to the eligible population if everyone comes forward to get one so we will have additional doses available [for boosters]," Hipkins said.
Medical director of the Royal New Zealand College of General Practitioners Bryan Betty said the evidence of boosters was "very much evolving at this point".
"It at very early stages," he said.
He said ordering booster shots would be "premature at this point".
"I think we would be jumping the gun on what is best practice is," he said.
Betty said that there will "no doubt" be Covid-19 booster shots administered on a periodic basis, but that it was too early to tell how long the interval should be between someone's second dose of vaccine and their first booster.
The study had not yet been peer-reviewed. It analysed data collected more than three million swabs collected in the United Kingdom as part of a longer survey conduced by the UK's Office of National Statistics.