ATAGI has endorsed use of Novavax’s COVID-19 vaccine as a booster when no other vaccine is suitable and tweaked its advice on AstraZeneca’s shot in an update for immunisation providers.

The committee previously suggested AstraZeneca’s vaccine, Vaxzevria, was a booster option for people who had it as a primary course but now recommends it as a booster “in those who have a medical contraindication to or who decline a booster dose of mRNA vaccine”.

New research suggests an mRNA vaccine booster after a primary course of Vaxzevria leads to a 10-fold higher increase in anti-spike IgG antibodies than a third or fourth Vaxzevria shot, according to ATAGI’s update, published on Wednesday.

“This is particularly important with Omicron becoming the dominant circulating SARS-CoV-2 variant, where higher antibody levels after the booster dose appear important for providing protection against Omicron.”

A booster dose of either approved mRNA vaccine, after any primary course, provided 50-75% effectiveness against infection and 80-95% effectiveness against hospitalisation with the Omicron variant, the committee said.

Vaccine effectiveness against symptomatic infection with BA.2, a sublineage of Omicron, was higher than for Omicron itself, it added.

Meanwhile, Novavax was expected to lodge a TGA application for its vaccine, Nuvaxovid, to be used as a boostr “shortly”, ATAGI said.

But in the meantime, GPs could administer the vaccine as a boostr ahead of TGA approval “if no other vaccine is suitable”.

In a phase II trial of about 3000 patients, a Nuvaxovid  generated lower antibody levels than a Comirnaty booster, both in patients who had received a primary course of Vaxzevria and those whose primary course was Pfizer’s Comirnaty, it added.

The Federal Government estimated that between 5% and 20% of the 900,000 Australian adults who were not vaccinated by January 2022 would be happy to get the protein-based vaccine.