2 Feb 2022

Shortened interval for Covid-19 vaccine booster key to limiting Omicron outbreak, experts say

6:29 pm on 2 February 2022

Experts are welcoming the shortening of the period between a second Covid-19 vaccine dose and the booster dose.

Nurses in the Far North Vaccinating during the lockdown

(File image) Photo: RNZ / Angus Dreaver

The change, which takes effect from this Friday, means that an additional million people will be eligible to get their booster dose. More than 1.3 million people have already got theirs.

Covid-19 modeller and Canterbury University professor Michael Plank* said boosting as many people as possible, as quickly as possible, would be crucial in managing the impacts of Omicron.

"With Omicron, getting the booster significantly reduces your own risk of getting seriously ill. It also reduces our collective risk that hospitals will be overwhelmed with Covid patients."

University of Canterbury professor, Michael Plank

Photo: Supplied.

The timing of boosters is all the more important with higher infection rates expected in the community over the coming weeks, and the immune system taking up to a week or two to respond to a vaccine dose, Prof Plank said.

"If you are eligible, please make a plan to get your booster and encourage your whānau and friends to do the same."

Te Pūnaha Matatini Covid-19 modeller Dion O'Neale** said by reducing the interval between the second and booster dose, there was a greater proportion of the population who would have access to increased protection.

"Data from the UK Health Security Agency indicates that for people three or more months after a second dose of the Pfizer vaccine, their protection against symptomatic infection is under 20 percent. This jumps to over 60 percent vaccine effectiveness against symptomatic infection after a booster dose."

The shortened period would also help address the issues seen during the initial Covid-19 vaccine rollout, Dr O'Neale said.

"Slower vaccination rates for Māori during the initial vaccine roll-out meant that a four-month wait would have left many ineligible for a booster over the next month when we are expecting Omicron cases to grow significantly.

"Reducing to a three-month interval to become eligible for a booster can help with not leaving people unprotected during this period.

"It is also important to note that eligibility is not the same thing as access. If the issues that led to slower uptake for some groups during the initial vaccine roll-out are not addressed for delivering boosters then we risk seeing the same people left with higher risk of infection and the possibility of severe health consequences."

Computational biologist David Welch, from the University of Auckland, said the country had the ability to administer more than 80,000 vaccine doses for a sustained period, and we should aim to achieve at least that.

"Reducing the interval for boosters from four months to three months is a sensible move and it will give people the ability to get the booster before encountering Omicron in the community.

"This will greatly increase the immunity we have in the population and reduce the impacts of the Omicron outbreak."

The shortened booster interval to three months only applies to the Pfizer vaccine. The Covid-19 Vaccine Technical Advisory Group will provide separate advice on AstraZeneca later this month.

Immunisation Advisory Centre director Nikki Turner told Checkpoint ideally there would be a longer gap between the second vaccine dose and booster, however, this was a good strategy to protect people in the face of rising Omicron infections.

"The immunity is effective from three months, it's just that you could hope for maybe more longevity for immunity with a longer gap. What we do know with Omicron is it comes into a country, it circulates for around three, maybe four months, so now is the time as a population [to get boosted], particularly for high risk people.

"We're expecting Omicron to go through New Zealand in a wave in probably about three months. So the peak of protection will be as Omicron goes through New Zealand."

Turner said it was looking likely that the situation would evolve so that those at high-risk of severe illness would continue to get boosters, rather than entire populations.

"Remember that not everybody's immunity will vanish at 10 weeks. Not everybody's the same, young healthy people will have immunity that lasts longer. Once again, our community will continue to have to protect those whose immunity drops off earlier.

"Immunity is not just about antibodies. You still have cellular immunity memory on board ... It's just that the antibody levels drop off."

*Conflict of interest statement: Michael Plank is partly funded by the Department of Prime Minister and Cabinet for research on mathematical modelling of Covid-19.

**Conflict of interest statement: Dion O'Neale is funded by the Department of Prime Minister and Cabinet to provide advice on the Covid-19 response and from a Health Research Council grant to look at equity related to Covid-19 in Aotearoa.

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