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Detailed modelling shows how declining immunity rates may affect case numbers in Queensland into 2022.

The modelling,commissioned by the Palaszczuk government and conducted by experts at QIMR Berghofer Medical Research Institute,predicted a large spike in cases about March 2022 if immunity declined in line with what had been seen in other parts of the world.

It showed there could be about 100 new COVID infections each day in Queensland by January if the state reopened at an 80 per cent vaccination rate under a simulated outbreak,and about 1000 new daily cases by mid-2022.

Infections would be highest 90 days after Queensland reopened at an 80 per cent vaccination rate,at which time there could have been about 100 deaths,with the over-65s age group making up most of those.

However,those figures assumed the overall immunity of people who had been vaccinated stayed unchanged,which might not be the reality.

Figures from overseas indicate the immunity of people who are fully vaccinated reduces over time,although the data is complicated and there is no consensus over how much and how quickly immunity wanes.

QIMR health modelling expert Dr James Roberts said the majority of their modelling assumed overall immunity rates would not change,which was not what had been seen overseas.

Health modelling expert James Roberts,one of the modelling’s authors from QIMR,said they wanted to give context in the modelling for what could happen if immunity levels did not stay consistent.

“We haven’t specifically modelled boosters,but we have suggested if there is a lot of waning[immunity] from the vaccine,then there is a possibility cases could climb at a much steeper rate,” Dr Roberts said.

“This suggests boosters do need to be considered.”

The federal governmenthas made a third dose of the vaccine available for the immunocompromised,based on advice from the Australian Technical Advisory Group on Immunisation.

However,there has not been any recommendation made on a third or booster dose for the general population.

Griffith University infectious diseases expert Nigel McMillan said it was no surprise immunity rates went down in vaccinated people over time,as that happened for almost every vaccine.

Professor McMillan said the Delta variant had “changed the game” because it was so much more infectious than previous COVID-19 variants.

“We had really good vaccine coverage and vaccinated people were not passing on infections nearly at all until Delta came along,” he said.

“This will only get worse and that is why boosters will be important for people to have.”

Professor McMillan said he believed boosters would eventually be rolled out widely,and they would consist of “version two” of the COVID-19 vaccine.

“Pfizer are working on a new vaccine,so are Novovax,they will be the important boosters for people to have,” he said.

The UQ vaccine,the development of which had to be abandoned late in 2020 because of false positives in other screening programs,is also in development again with an eye on being a good booster shot as well as a first dose for anyone not vaccinated.

Queensland Health Minister Yvette D’Ath said the government was aware of the need for booster shots and would probably prioritise people in aged care if they were approved by the TGA and recommended by ATAGI.

“[Aged care residents] were the people who first got vaccinated back in February of this year,so they will need to get a booster shot,” Ms D’Ath said.

“But what we say is before you worry about whether you’ll need a third shot,how about you get your first shot.”

On Tuesday,72.47 per cent of Queenslanders aged over 16 had received their first dose,while 56.9 per cent were fully vaccinated.

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