But as a young person seeking AstraZeneca, his path to inoculation was somewhat pocked.

"My regular GP told me AZ was a second rate vaccine and that the situation was not so dire that I needed a shot," the 27-year-old Sydneysider told AAP.

The conversation, a couple of weeks into the city's lockdown, ended with the advice Mr Hemmings wait for Pfizer.

Instead, he sought a second opinion, booking an appointment online with a doctor he'd not consulted before who gave him the shot he wanted on Thursday.

"I respect the opinion of my GP but I've done the risk calculus and getting vaccinated is more important than waiting for the perfect vaccine," Mr Hemmings says.

Melbourne woman Jeanette Wong also asked her GP in late July for more information on AstraZeneca.

"I've done my own research but you want to talk to a medical professional," she told AAP.

"Immediately, he was like 'No, you're in your 30s, you're healthy just wait for Pfizer'.

"He just did not want to talk about it objectively at all. He started scaring me, saying 'people are taking the AZ and are getting paralysed'."

Another clinic she enquired with wouldn't accept her as she is Singaporean and without Medicare coverage, leaving her unvaccinated for now as her city enters its sixth lockdown of the pandemic.

About 340,000 Australians under 50 have had at least one dose of AstraZeneca compared to 2.4 million with Pfizer.

They're among five million people overall who've received AZ - most of whom are over 60.

Australia's expert vaccine panel, ATAGI, says AstraZeneca is "very effective" at preventing severe disease and death in all ages from COVID-19.

But its nuanced and changing advice, the multiple risk-benefit scenarios and initial widespread publicity surrounding rare blood clots has confused even doctors, says AMA Vice President Chris Moy.

A lot of discussion with the patient is required and the government's no-fault indemnity scheme, taking the burden off doctors and their insurers, remains unfinalised.

"Without feeling completely backed in about that, some doctors don't feel comfortable prescribing it, especially when they perceive either complexity or ambiguity in the interpretation of ATAGI guidelines," Dr Moy says, noting GPs have no obligation to administer medications patients demand.

Father-of-one Alex Harvey was ready to get the jab in a northern Sydney clinic in July, only for a doctor to come in and "double-check I really understood that it's not recommended".

With his AstraZeneca-hesitant partner alongside him, the 47-year-old was talked into double-checking whether he could not find a Pfizer booking.

"A week later, it was clear Pfizer was not an option without waiting months anyway, so I went back a second time and got it done," he says.

Mr Harvey is satisfied with his decision, believing AstraZeneca may be the superior vaccine and noting its technology has been used in flu vaccines for more than a decade.

Victorian writer Miranda Luby tried six clinics before finding one willing to book her in for AstraZeneca.

She waited 40 minutes in the clinic on Friday - hours into a statewide lockdown - before seeing a teary doctor uncomfortable with giving the shot to a 33-year-old because of the ATAGI advice.

"She said go home, stay home, wait for Pfizer," a furious Ms Luby later tweeted.

"I'm not angry at the doctor, who was just trying to do what she feels is the right thing ... I'm angry at this gaslighting, f***ing government that is screaming at us to get vaccinated ASAP and running ads of young people suffocating and is setting up to blame us when things aren't going well months down the track."

Those doctors willing to administer jabs, however, have been the backbone of Australia's rollout.

Nearly 60 per cent of last week's 1.3 million shots were delivered by GPs and other primary carers.

Dr Moy says the Delta coronavirus variant has made the risk-benefit equation easier, showing there's little time between a no-threat and high-threat situation.

He also sees a broader psychological factor at play - vaccine success is virtually silent.

"For some doctors, the fear of feeling responsible for a patient suffering a rare side effect of a medication, even if it's incredibly rare, is closer and more tangible than the much greater benefit in the number that will be protected and saved but who will never know it," he says.

Even Queensland's top doctor changed tack last week, having been among the most vocal experts against young people receiving AstraZeneca.

"This is the time that people who are under age 60 should be talking to their GP about what is best for them as an individual, GPs know their patients," Dr Jeanette Young said on Tuesday after announcing further new virus cases in her state.

As with other medical consultations, Dr Moy says young people not happy with their GP's advice can seek a second opinion.

"(Many GPs) can see the overall threat is there and they understand the benefits of vaccination," the SA doctor says.

The online system Mr Hemmings used - HotDoc - this week rose to No.6 on both Apple and Google's app charts.

More than four million COVID vaccine appointments had been booked across Australia on its system, the company says.

Mr Hemmings, who noted a large number of people filling in new-patient forms at the clinic that vaccinated him, says he's aware of the clotting risk.

"But I'm also aware that my risk of clotting is higher with COVID-19," Mr Hemmings says.

"The perfect is the enemy of the good and frankly I don't want to contract COVID and end up in the ICU or die."

Australian Associated Press