Covid 19 coronavirus Delta outbreak: Does immunity from Pfizer vaccine wane, and should MIQ workers get booster shots now?

There are 35 new cases of Covid-19 in the New Zealand community to confirm today. Of these 33 are in Auckland and two are in Wellington. Video / NZ Herald

ANALYSIS:

Are fully vaccinated quarantine workers at risk as they care for the 154 border and community cases of Covid-19 in the country at the moment?

And should the Government use a fraction of the 750,000 doses of the Pfizer vaccine we have in reserve to give these workers a booster dose?

The answer to the first question is complex, according to immunology experts, but two doses still provide excellent protection.

The answer to the second, so far, is "no".

The questions are arising as recent studies suggest waning immunity from Pfizer against the Delta variant - some as low as 39 per cent against infection, though the vaccine still protected people from severe health impacts.

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Experts say Pfizer continues to be effective, and it's too early to say whether booster shots for frontline border workers - who started having their first dose six months ago - are needed.

"We know immunity is holding well for over six months, and our earliest vaccinations were in February," says Dr Nikki Turner, director of the Immunisation Advisory Centre.

Protection against mild and asymptomatic carriage was lower with the Delta variant, she said, but "that is not related to waning immunity".

Immunisation Advisory Centre director Dr Nikki Turner says protection from the Pfizer vaccine is still "holding up well" six months after a second dose. Photo / Mark Mitchell

Among some recent studies is one via the Mayo Clinic Health System - looking at a time period of January to July 2021 in Minnesota - which said that Pfizer was 42 per cent effective against infection by July.

A study in Qatar found Pfizer was 53.5 per cent effective against any Delta infection at least 14 days after the second dose in a population, "in a population in which a large proportion of fully vaccinated persons received their second dose several months earlier".

The Health Ministry in Israel, where Delta is rampant, recently said Pfizer was 39 per cent effective against infection, but it still provides strong protection against severe illness and hospitalisation.

And an Oxford University study, based on more than three million nose and throat swabs taken across Britain, found efficacy for the Pfizer vaccine falling from 85 per cent two weeks after a second shot to 75 per cent after 90 days.

Chief investigator of that study, Sarah Walker, noted that the protection level was still "doing really well" against Delta.

Nikki Turner told the Herald that there was no compelling case so far to start giving booster shots to frontline workers.

"We are all continuing to review data as it comes in and are watching waning immunity closely. It varies with environment.

"It is possible that particularly higher-risk groups may need boosting next year."

Auckland University vaccinologist Dr Helen Petousis-Harris said there was yet to be a study in a controlled environment, without which there are several variables affecting the data.

"One thing is a change in behaviour. If you look at Israel, they spent a lot of time in lockdown, which then eased off. And there are different schedules between doses in different studies, which is likely to make a difference.

"Countries have also vaccinated starting with the oldest people. All of that really makes it very complex."

She added that offering booster shots while others have had no vaccine dose could create ethical issues.

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The Government could still decide there was enough of a trend in enough studies to warrant boosting MIQ workers, starting with those who have contact with any of the quarantine wings.

Waning immunity was something director general of health Ashley Bloomfield said he was "keeping an eye on".

"The studies about waning immunity are still in their early days, it's really a watch and wait at the moment."

The Government is yet to order any more than the 10 million doses it has already bought from Pfizer, partly because it remains to be seen if the next order should be for the current vaccine, or for one that has been tweaked for any variants.

Even if everyone who is eligible becomes fully vaccinated, there should still be about 1.3 million doses left over to at least start a booster programme, if needed.

"Of course, we're in conversations [with Pfizer] to make sure that we have vaccine supplies available next year, canvassing all of the different options and looking at what our needs will be," Covid-19 Response Minister Chris Hipkins said yesterday.

"We'll make that decision, as we always do, based on the best health and science advice available."