The world-first Covid-19 alternating dose vaccine study launched on Thursday, February 4, 2021 in the UK will examine whether different vaccines can safely be used for 2-dose regimes in the future. According to a press release from the UK Government, participants in the clinical trial will receive different vaccines for their first and second doses. As of now, the vaccines being rolled out are administered to people in two doses with shots of the same kind, weeks apart. The move comes as countries around the world race to inoculate their people against Covid-19 and tackle new variants resulting from its mutating coronavirus, and the logistic challenges around vaccinations. The development is trying to enhance this effort by mixing and matching different shots. Currently, apart from the single-dose Covid-19 vaccine developed by Johnson & Johnson, other vaccines developed so far use a two-dose regimen. Backed by £7 million of government funding, the 13-month study will be the first in the world to determine the effects of using different vaccines for the first and second dose – for example, using Oxford University/AstraZeneca’s vaccine for the first dose, followed by Pfizer/BioNTech’s vaccine for the seconds. The two vaccines are approved for use in the UK. The study, run by the National Immunisation Schedule Evaluation Consortium (NISEC) across 8 National Institute for Health Research (NIHR) supported sites, will also gather immunological evidence on different intervals between the first and second dose for a mixed-vaccine regimen against control groups when the same vaccine is used for both doses. Meanwhile, the statement indicated that there are no current plans to change the current programme of two doses of the same vaccine over 12 weeks remains unchanged. The study will monitor the impact of the different dosing regimens on patients’ immune responses, which have the potential to be higher or lower than from the same dose regimen. Initial findings are expected to be released in the summer. The study has received ethics approval from the Research Ethics Committee, as well as approval from the Medicines and Healthcare products Regulatory Agency (MHRA). Should the study show promising results, then the government may consider reviewing the vaccine regimen approach if needed, but only if proven to be safe and recommended by the Joint Committee on Vaccination and Immunisation (JCVI). The UK Minister for COVID-19 Vaccine Deployment, Nadhim Zahawi, said that “this is a hugely important clinical trial that will provide them with more vital evidence on the safety of these vaccines when used in different ways.” Deputy Chief Medical Officer and Senior Responsible Officer for the study, Professor Jonathan Van-Tam, said that given the inevitable challenges of immunising large numbers of the population against Covid-19 and potential global supply constraints, there are definite advantages to having data that could support a more flexible immunisation programme, if needed. “It is also even possible that by combining vaccines, the immune response could be enhanced giving even higher antibody levels that last longer; unless this is evaluated in a clinical trial we just won’t know,” he observed. Over 800 volunteers are expected to take part in the study, referred to as the COVID-19 Heterologous Prime Boost study or ‘Com-Cov’, across 8 different sites across England – including in London, Birmingham and Liverpool. The participants will be recruited over the course of February via the NHS COVID-19 Vaccine Research Registry, with vaccinations expected to start towards the middle of the month and initial results to be made available over the summer period. Chief Investigator Matthew Snape, Associate Professor in Paediatrics and Vaccinology at the University of Oxford, said this is a tremendously exciting study that will provide information vital to the roll out of vaccines in the UK and globally. “If we do show that these vaccines can be used interchangeably in the same schedule this will greatly increase the flexibility of vaccine delivery, and could provide clues as to how to increase the breadth of protection against new virus strains,” he said. On 25 January 2021, the UK government issued guidelines stating that there was no evidence on the interchangeability of the COVID-19 vaccines. However, it stated that for individuals who started the schedule and who attend for vaccination at a site where the same vaccine is not available, or if the first product received is unknown, it is reasonable to offer one dose of the locally available product to complete the schedule. This option, it pointed out, is preferred if the individual is likely to be at immediate high risk or is considered unlikely to attend again.
