Our jab strategy ‘won’t achieve herd immunity’

Australia will not achieve herd immunity with its current vaccine strategy of using the Pfizer and AstraZeneca jabs, a University of Sydney study says.

Syringes filled with the Pfizer COVID-19 vaccination are ready for patients in Sydney. Picture: Bianca De Marchi

Australia will not achieve herd immunity with its current vaccine strategy of using the Pfizer and AstraZeneca jabs, a University of Sydney study says.

Researchers at the University of Sydney’s Centre for Complex Systems modelled Australia’s hybrid approach of using the Pfizer vaccine to inoculate part of the population and relying on the AstraZeneca shot to vaccinate the bulk of the population.

The study, which has not been peer-reviewed, found herd immunity would not be reached using this strategy even if 90 per cent of the population was to be vaccinated.

The team of researchers, led by modeller Mikhail Prokopenko, who also conducts research as part of the Marie Bashir Institute for Infectious Diseases and Bio­security, found herd immunity would be achieved if the high-­efficacy Pfizer vaccine was used alone and 70 per cent of the population was vaccinated.

But vaccinating 10 million people with Pfizer and using Astra­Zeneca — which was found in clinical trials to have an efficacy of 70 per cent — for the rest of the population meant herd immunity would not be achieved.

Lead author Cameron Zach­reson said modelling indicated the hybrid vaccine strategy would result in continuing outbreaks that would grow exponentially.

“Herd immunity is not possible under the current scheme,” Dr Zachreson said.

“That means future outbreaks will spread, and that means there’s the possibility that governments may decide to introduce lockdowns like we saw in previous outbreaks.

“Basically what we’re looking at is a scenario where instead of going for herd immunity, we’re setting ourselves up for a low level of COVID spread that we simply have to deal with, and the clinical outcomes should be less severe.”

Health Department secretary Brendan Murphy said this week that real-world data from the UK, which has vaccinated more than 11 million people with AstraZeneca and millions more with Pfizer, showed both vaccines were “equally efficacious”.

“They are both very, very good vaccines that prevent severe disease, hospitalisation in all age groups, including the elderly.”