The government is set to tweak its vaccination timetable to accelerate jabs for those aged 30 to 39, after Doherty Institute modelling showing it is vital to get younger adults quickly vaccinated, because they are high COVID transmitters.

Those in their 30s and 20s – scheduled for the Pfizer vaccine – are at the back of the queue under the rollout plan, becoming eligible from September-October, according to the man in charge of the rollout, General JJ Frewen, speaking some weeks ago.

With Pfizer in short supply, they are now under some pressure, including from Scott Morrison and changing health advice, to take the AstraZeneca vaccine.

Government sources said on Tuesday the plan would be tweaked, probably this week, after incoming Pfizer supply numbers were confirmed.

The Doherty modelling, used as a basis for national cabinet last week setting vaccination targets, says: “As supply allows, extending vaccinations for adults under 40 years offers the greatest potential to reduce transmission now that a high proportion of vulnerable Australians are vaccinated.”

The vaccine uptake by young people 16 and over “will strongly influence the impact of vaccination on overall transmission,” Doherty says.

The modelling was released on Tuesday at a news conference by Scott Morrison and Professor Jodie McVernon, Director of Epidemiology at the Doherty Institute.

McVernon said the 20 to 39 year olds were “the peak spreaders” of the virus.

“They will bring COVID home to their children, they will take it home to their own parents, and this is the group now where we’re proposing the reorientation of the strategy,” she said.

National cabinet last week agreed in principle to a four stage plan to move from the present suppression strategy (aiming for zero community transmission) to a limited reopening when 70% of people 16 and over have been fully vaccinated. When the vaccination level reached 80%, lockdowns would be rare and limited.

In an analysis for the national cabinet meeting, Treasury calculated the direct impact on economic activity of various vaccination scenarios modelled by Doherty.

Treasury found that “continuing to minimise the number of COVID-19 cases, by taking early and strong action in response to outbreaks of the Delta variant, is consistently more cost effective than allowing higher levels of community transmission, which ultimately requires longer and more costly lockdowns.”

At 50% vaccination rates, the direct economic cost of minimising cases is about $570 million a week; at 60%, it is about $430 million.

At 70%, with only low level restrictions needed, the expected economic cost of COVID-19 management falls to about $200 million each week, reducing to about $140 million at an 80% vaccination level.

Treasurer Josh Frydenberg said the clear message from the economic modelling “is that until we get to 70% and above vaccination rates, the economic imperative is that governments need to move fast to get on top of those cases. If they don’t, we see lengthier and more severe lockdowns, which have a much more significant economic cost.”

“What Treasury have found is that at 50% and 60% vaccination rates, it’s five times more costly, should governments not move early to get on top of the virus.”

The NSW government has recently come under sharp criticism for not moving earlier in the current Sydney outbreak. There is now a prolonged lockdown.

Despite Australia’s still low vaccination rate – only about one in five 16 and over have had two doses – Morrison strongly rejected Anthony Albanese’s proposal that everyone who is fully vaccinated by December 1 should receive $300.

Morrison said the proposal was “a vote of no-confidence in Australians”, and “a bubble without a thought”. It said to people that health concerns they might have about a vaccine could be paid off.

Pointing to the relatively high level of take-up by older people Morrison said: “Do we really think that Australians of younger ages are less committed to their own health, the health of their families, the health of their communities, than those who are older? Of course not.”

“It’s not a game show. And it’s very important that we continue to respect how Australians are engaging with this process. So if they do have hesitancy about vaccines, I’m not going to pay them off. I’m going to pay a GP to sit down with them and talk them through their concerns, which is what I have already done.”

The Essential poll, released Tuesday, found 47% of people who have not been vaccinated say they would take Pfizer but not AstraZeneca. This unwillingness to receive AstraZeneca has increased substantially since April.