Morrison said Australians should get the second dose of the AstraZeneca vaccine in the early part of the eight to 12-week waiting period.
Prime Minister Scott Morrison has urged Australians to get their second dose of the AstraZeneca vaccine after two months instead of three.
His plea came as the highly contagious Delta variant continued to sweep across Sydney despite a lockdown there.
The AstraZeneca jab requires two doses, which are recommended to be received up to 12 weeks apart, but the health advice allows for a shorter time if there is a risk of COVID-19 exposure.
What did the Prime Minister say?
Mr. Morrison said Australians should get the second dose of the AstraZeneca vaccine in the early part of the eight to 12-week waiting period.
His comment came after he spoke about the growing number of COVID-19 cases in south-western Sydney.
"We would also be encouraging the eight to 12-week the second dose to be done at the earlier part of that eight to 12-week period.
That is consistent with medical advice, the TGA approval does sit and ATAGI advice on eight to 12 weeks.
And given the risks to people of the outbreak in that area, we believe it's important that they get the second dose of AstraZeneca as soon as possible.
That is the community that is most at risk in these circumstances."
What is ATAGI advice?
The independent Australian Technical Advisory Group on Immunisation (ATAGI) says the recommended interval between two doses of the AstraZeneca vaccine is 12 weeks.
ATAGI says the efficacy — or effectiveness — of AstraZeneca is higher after a longer time between doses.
"Efficacy against symptomatic COVID-19 ranges from about 62 percent to 73 percent, with the higher efficacy seen after a longer interval (12 weeks) between doses.
Efficacy from day 22 after the first dose up until 12 weeks is about 73 percent."
This is in line with research looking at the differences in AstraZeneca's efficacy based on vaccine timing.
A study involving more than 17,000 participants, published in the medical journal The Lancet in February, found that a three-month gap between the first and second dose could have advantages over a shorter one.
The vaccine had about 81 percent efficacy if the second dose was given 12 weeks after the first, but that dropped to 55 percent if the gap was six weeks or less, the study indicated.
But no matter what, two doses are better than one and some countries have shortened the interval in order to get more people fully vaccinated faster.
The World Health Organization says longer dose intervals within the eight to 12 weeks are associated with greater vaccine efficacy.
Can the second dose of AstraZeneca be less than 12 weeks?
Yes, ATAGI says the minimum interval between doses is no less than four weeks.
It says this may be "acceptable and may be appropriate in certain circumstances, for example, imminent travel or anticipated risk of COVID-19 exposure".
Epidemiologist Mary-Louise McLaws said reducing the time between doses was a good idea in light of the Delta strain outbreak in Sydney.
Professor McLaws said moving from a 12-week gap to an eight-week gap would "reduce your risk of dying, it will reduce your risk of hospitalisation, but will not protect you all from symptomatic or asymptomatic infection".
"The idea of moving a second dose forward will be a good idea, but we may have to have a booster shot after that," she said.
"Because if we start moving away from that 12 weeks, your antibody response may not be as good as it could be.
"But given that we are in dire straits at the moment with Delta, we do not want it to go across any state borders, we do not want it to go to the elderly.
"It is a good idea."
Are other countries shortening the wait time?
The United Kingdom brought forward the second dose of the AstraZeneca jab from 12 weeks to eight weeks in a bid to accelerate its vaccination programs.
Its decision last month came after updated advice from the Joint Committee on Vaccination and Immunisation, which recommended reducing the waiting period to counter the threat of new variants, including Delta.
Several provincial Canadian governments have also shortened the wait time between doses of the AstraZeneca jab to eight weeks.