A $17.6 million, CEPI-funded research program spanning Australia, Indonesia, and Mongolia has found that fractional — or half — doses of COVID-19 vaccines produce immune responses comparable to full doses over time, according to results from the Murdoch Children’s Research Institute.

The program tracked more than 2,000 participants across three randomised trials over as long as two years. In Indonesia, a study of more than 1,200 adults comparing Pfizer, AstraZeneca, and CoronaVac vaccines was published in Nature Communications. In Mongolia, a trial of 601 adults receiving fractional doses of the Pfizer vaccine was published in Frontiers in Immunology. And in Australia, a study of 496 adults comparing mRNA and protein-based fourth doses was published in the Journal of Infection — a result that has since secured an additional $2 million in funding from Australia’s National Health and Medical Research Council to extend follow-up to 30 months.

A related study, published in the journal Vaccine, found that morning vaccination produced a better immune response to mRNA vaccines than afternoon vaccination.

“These findings give us confidence that dose-sparing strategies can maintain strong, lasting protection,” said Dr Nadia Mazarakis, one of the researchers involved. CEPI’s Amol Chaudari, and MCRI’s Associate Professor Paul Licciardi and Associate Professor Claire von Mollendorf, were also central to the work, which the team says could help stretch vaccine supplies further in future outbreaks.

Journal: Journal of Infection
DOI: 10.1016/j.jinf.2026.106727
Publication Date: 16 July 2026

Source: EurekAlert