GPs split over dosing interval for AstraZeneca Covid-19 vaccine

Doctors say they will decide on a ‘case-by-case basis’ whether to give the AstraZeneca vaccine to patients as soon as eight weeks after their first dose.

President of the Australian Medical Association (NSW), Danielle McMullen. Picture: Jonathan Ng

Doctors say they will decide on a “case-by-case basis” whether to give the AstraZeneca vaccine to patients as soon as eight weeks after their first dose as thousands of people rush to gain earlier ­appointments.

The nation’s chief medical officer, Paul Kelly, has endorsed advice that people in Covid-19 hotspot areas of Sydney should be given their second AstraZeneca vaccine eight weeks after their first dose instead of 12.

The advice has seen patients around Australia inundate doctors’ surgeries to ask whether they can also shorten the interval between their first and second AstraZeneca shots, but general practitioners have been giving differing advice.

The president of the Australian Medical Association (NSW), Danielle McMullen, said Scott Morrison’s announcement about shortening the dosing interval came as a surprise to doctors.

“We weren’t given any warning that a change or a change of guidance was imminent,” Dr McMullen said. “GPs have been flooded with calls.

“We do know that a 12-week interval gives you better protection, but given the Sydney outbreak, it does seem reasonable that if people want to bring forward their second dose to eight or 10 weeks, they can do that providing they can get an appointment.

“We’ve got to remember that GP clinics are already booked up with people who have booked their 12 week dose. Clinics may or may not have the capacity in the vaccine supply to be able to bring forward doses.”

A study in the Lancet published earlier this year found that the AstraZeneca vaccine provided 81.3 per cent protection when two doses were given 12 weeks apart, but efficacy fell to 60 per cent when doses were given between six and eight weeks apart.

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Efficacy was 63.7 per cent when doses were given between nine and eleven weeks apart.

Deputy chair of the Australian GP Alliance Mukesh Haikerwal called for clarification on the dosing interval from the Australian Technical Advisory Group on Immunisation. “The recommendation on the product infor­mation is four to 12 weeks between doses. We know the nearer you are to 12 weeks, the better, but how about our advisers gives us some direction?”

The Therapeutic Goods Administration has approved AstraZeneca vaccine doses to be given between four and 12 weeks apart.

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Federal AMA vice-president Chris Moy said the recommendation to shorten the dosing interval was sensible: “Given the situation in NSW, with a very urgent need to try and have people fully vaccinated as far as possible and protected as quickly as possible, it’s a reasonable balance.”

The change of advice in NSW comes as a study published in the scientific journal Nature found one dose of a Covid-19 vaccine provided minimal protection against the Delta strain because the variant had mutations that allowed it to evade some of the neutralising antibodies produced by vaccines or by natural infection but two doses of a ­vaccine provided “substantial” protection.

 

In the US, Pfizer announced it would seek clearance from regulators to distribute a booster shot of its Covid-19 vaccine in fully vaccinated people, based on initial study data that found a third shot increased protection.

In Australia, social media was flooded with posts from people who had tried to get their second AstraZeneca shot sooner but had been knocked back by doctors.

Sydney GP Kean-Seng Lim said patients were given advice on an individual basis. “As a GP, I need to make an individual assessment of risk for every person … in the context of the prevalence of the virus in the community,” Dr Lim said. “Changing from a 12-week interval to an eight-week interval will require significant adjustments at general practice level.”