Scientists in Britain are examining whether smaller doses of Covid vaccine could be used as part of booster programmes, amid hopes that the approach could also increase the supply of jabs across the world. The use of so-called “fractional doses” has been proposed as a way of ensuring that precious supplies can immunise as many people as possible in parts of the world where there are shortages, while still providing high levels of protection from the virus. Several members of the Joint Committee on Vaccination and Immunisation (JCVI), which advises the UK government, are said to be interested in the idea. Lower doses of vaccines to tackle other diseases have been used in times of shortage. The JCVI is expected to rule out an immediate booster vaccine programme for all adults as it waits for more research to emerge, although the government is poised to proceed with follow-up jabs for those most at risk and in need of a boost to their immunity. This could start as early as next month. Hospital admissions and deaths from the virus rose slightly last week, with about 100 deaths reported each day. The effect of using lower doses in booster jabs is one of the questions being explored in an ongoing Cov-Boost trial being overseen by University Hospital Southampton. It has been funded by the government’s vaccine task force and the National Institute for Health Research. Its findings will inform the JCVI’s decisions about an autumn booster programme, alongside data from other trials and studies. Researchers are examining the safety and side effects of different doses, as it is possible that lower amounts of vaccine could boost immune responses while reducing the risk of side effects. Different vaccines could also behave in different ways. Some epidemiologists would like to see more studies commissioned because of the potential to help with global vaccine supplies. It is estimated that about 11 billion doses will be needed to fully vaccinate 70% of the world’s population. At the start of July, only 3.2 billion jabs had been administered. Researchers estimate that many of the world’s poorest will have to wait until 2023 for a vaccine. Some research into fractional doses has already been carried out. A paper led by Prof Benjamin Cowling, an epidemiologist at the University of Hong Kong, argued recently that the use of lower doses “is a potential solution to this global shortage of vaccines that has not been given sufficient attention and consideration”. Some researchers have warned that it is possible the approach could lead to greater vaccine resistance, but that could be offset by fewer people being infected. David Hunter, a professor of epidemiology and medicine at Oxford University, said the idea of reducing doses had been deployed in the fight against other diseases. “Stretching the vaccine supply further by administering lower doses of the antigens has been a strategy used in emergency situations when ebola and polio vaccine supplies were limited,” he said. “The basic idea is to immunise more people with the same supply. The key question is whether for each individual, vaccine efficacy is reduced, and if so, by how much. “It is plausible that booster shots could be given at a lower dose than first and second shots. Studies are under way for several Covid-19 vaccines to assess this. If a lower dose proves to only slightly diminish efficacy, then national regulators will need to consider the potential international benefits of increasing the number of shots available. It will be critical that this be done in a way that does not cause vaccine hesitancy due to a perception that the reduced dose shots are inferior.” Prof Danny Altmann, an immunologist at Imperial College London, said that the global shortage was more to do with distribution than supply. He added that there was potential to explore dosage amounts. “Vaccine dosing, like all else in the past 18 months, has been a case of building the plane while we fly, so there’s infinite potential to set up [randomised controlled trials] to revisit maximising spread of doses. This was done enormously effectively to deal with the production shortfall in yellow fever vaccine doses.” A spokesman for the Department of Health and Social Care said a booster programme was being prepared for the most vulnerable people in Britain. “Any booster programme will be based on the final advice of the independent JCVI. Until we receive the independent JCVI advice, no decisions can be made on wider requirements for those who receive booster jabs. ‘The UK is committed to supporting a global recovery to the Covid-19 pandemic and improving access to vaccines – and we will donate 100 million surplus vaccine doses within the next year as well as backing Covax to distribute 1.3 billion doses to 92 developing countries.” The headline of this article was amended on 22 August 2021 from “scientists look at halving boosters” to “scientists look at reducing boosters” to more closely align with the text of the article.