Fractional COVID booster doses provide strong long-lasting immunity

The trials found fractional doses, where people receive half the standard vaccine amount given as boosters, produced strong immune responses that remained comparable to full-dose boosters.

CEPI Clinical Development Science Lead Amol Chaudari said, "These pivotal insights - produced across different countries, with different vaccines and people who had received different first COVID vaccine doses - essentially show that public health officials can get 'more bang for their buck' with COVID vaccine boosters. If COVID cases were to ramp up again and there be strain on the vaccine supply, these findings could be key to expanding vaccination coverage quickly and preventing future infections and deaths. The findings could also prove helpful for future vaccines against other coronaviruses manufactured using similar technologies."

Additional research from the team published in Vaccine, found vaccination in the morning, rather than afternoon, improved responses to the mRNA vaccine, but not the protein-based vaccine. The findings suggest simple changes to vaccination timing may offer meaningful benefits.

"This knowledge can also help future public health strategies to combat emerging pathogens like hantavirus, Ebola and mpox."

MCRI Associate Professor Claire von Mollendorf said, "These trial results demonstrate that shaping effective public health policy requires monitoring long-term immune responses across diverse settings with variable infection rates and different primary vaccine schedules."

Source:

Murdoch Childrens Research Institute

Journal references:

John D. Hart, Eddy Fadlyana, Nadia Mazarakis, Nina Dwi Putri, Emma Watts, Kerryn A. Moore, Eleanor F. G. Neal, Djatnika Setiabudi, Muhammad Gilang Dwi Putra, Cattram Nguyen, Aqila Sakina Zhafira, Pratama Wicaksana, Robert Sinto, Dwi Oktavia, Rini Fajarani, Agnes Rengga Indrati, Chrysanti Murad, Yovita Hartantri, Hendarsyah Suryadinata, Yulia Sofiatin, Kusnandi Rusmil, Hindra I. Satari, Sri Rezeki. Hadinegoro, Cissy B. Kartasasmita, Julitasari Sundoro, Paul V. Licciardi, Claire von Mollendorf and Edward K. Mulholland. 'Immunogenicity of fractional and standard dose COVID-19 vaccine boosters among healthy adults in Indonesia: twenty four month follow-up from a randomised controlled trial,' Nature Communications. DOI: 10.1038/s41467-025-63598-6

Tsetsegsaikhan Batmunkh, Eleanor FG Neal, Otgonjargal Amraa, Nadia Mazarakis, Bolor Altangerel, Naranbaatar Avaa, Lkhagvagaram Batbayar, Khishigjargal Batsukh, Kathryn Bright, Tsogjargal Burentogtokh, Lien Anh Ha Do, Gantuya Dorj, John D Hart, Otgonbold Jamiyandorj, Khulan Javkhlantugs, Sarantsetseg Jigjidsuren, Frances Justice, Shuo Li, Khaliunaa Mashbaatar, Kerryn A Moore, Narantuya Namjil, Cattram D Nguyen, Batbayar Ochirbat, Unursaikhan Surenjav, Helen Thomson, Bilegtsaikhan Tsolmon, Paul V Licciardi, Claire von Mollendorf and Kim Mulholland. 'Fractional BNT162b2 boosters induce durable immune responses after non-mRNA priming in Mongolia: a randomised controlled trial,' Frontiers in Immunology. DOI: 10.3389/fimmu.2026.1789248