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The findings support the most up-to-date recommendations for individuals to get their booster shots without delay, to maintain high immunity levels in the population. 

The optimal timing for booster shots following the last COVID-19 vaccination or infection has remained unclear, with guidance on the interval between boosters varying widely. When COVID-19 vaccines were first released, some studies found that increasing the interval between your first two doses improved antibody immunity against SARS-CoV-2. To elucidate whether these findings remain true for subsequent booster vaccines, researchers conducted a randomised clinical trial to determine if delaying a COVID-19 booster vaccine by three months improved immunity against SARS-SoV-2. 

University of Melbourne’s Dr Wen Shi Lee, Research Officer at the Doherty Institute, said the findings, published in The Journal of Clinical Investigation, showed there is no advantage to delaying booster vaccination in a pre-immune population. 

“We observed no difference between participants who received the booster immediately and those who got it three months later. Both had the same immune responses, with similar increase in neutralising antibodies, which help protect against the virus, in blood and saliva,” said Dr Lee, the paper’s first author.  

“The incidence of symptomatic and asymptomatic SARS-CoV-2 infection was also similar between both groups, with about half of the participants experiencing infection in the period of up to a year following booster administration.” 

Moderna's bivalent Spikevax, the mRNA COVID-19 booster vaccine used in the trial was effective in triggering an immune response against Omicron strains. However, the research team found that the increased antibody levels were short-lived, waning significantly by day 84 and returning to pre-booster levels by day 240. This highlights the need for vaccines offering longer-lasting protection and broader immunity against SARS-CoV-2. 

University of Melbourne’s Professor Stephen Kent, Laboratory Head at the Doherty Institute and senior author of the study, said their work demonstrates the importance of maintaining robust COVID-19 booster programs to sustain immunity levels in the population, especially as the virus continues to evolve. 

“Our research shows that if it has been a long time since you were last vaccinated or infected with COVID-19, delaying your booster does not lead to better immunity. So, if you are eligible, go ahead and get your booster shot,” said Professor Kent.  

The Department of Health and Aged Care advises that all adults receive COVID-19 booster vaccinations every 12 months to maintain optimal protection against severe illness, hospitalisation and death from COVID-19. This is particularly recommended for people aged 65 years or older and people at higher risk of severe COVID-19. 

• Peer review: Lee W.S, et al. Randomised controlled trial reveals no benefit to a 3-month delay in COVID-19 mRNA booster vaccine. The Journal of Clinical Investigation (2024). https://doi.org/10.1172/JCI181244 
• Collaboration:  The clinical trial was conducted with the Royal Melbourne Hospital. 
• Funding: The National Health and Medical Research Council (NHMRC) and Medical Research Future Fund (MRFF), with additional support from the Australian Government and Moderna.