Mixed Covid-19 vaccine schedules are an effective way to protect young people from the virus, according to new research.
Using both the Pfizer-BioNTech vaccine and the Novavax vaccine, UK researchers led by the University of Oxford have shown that mixing vaccines and the combined use of full and fractional doses given at a later date provide ‘a greater breadth’ of protection against Covid-19 infections in adolescents.
The findings, published in the Journal of Infection, could allow greater flexibility in vaccine schedules and improve Covid-19 vaccine supply globally.
As part of the Com-COV3 study, the researchers examined the effects of mixed and fractional doses of Covid-19 schedules on 148 12- to 16-year-olds. By looking at immune response and the side effects of mixed doses of vaccines, the researchers were able to establish the effectiveness of administering a full first dose of the Pfizer-BioNTech vaccine followed by either a one-third (fractional) dose of the Pfizer-BioNTech vaccine or a full dose of the Novavax vaccine at least eight weeks after the initial dose.
Both a mixed vaccine schedule and a vaccine schedule with a partial second dose were well-tolerated in young people and generated a robust immune response that lasted for at least eight months.
Using a full dose of the Pfizer-BioNTech vaccine followed by a full dose of Novavax was more effective than following the first Pfizer-BioNTech vaccine with a second full dose of the Pfizer-BioNTech vaccine. The mixed vaccine schedule led to fewer breakthrough infections and generated higher antibody responses against various Covid-19 variants, including wild-type and Omicron variants, BA.1 and BA.2.
The study raised no vaccine safety concerns, and the side effects for all mixed and non-mixed vaccine schedules were favourable. The participants given a smaller second dose of the Pfizer-BioNTech vaccine reported fewer and milder side effects than those given full second doses.
Dr Angela Minassian, Chief Investigator on the trial from the Oxford Vaccine Group, said: ‘This study has embodied an incredible effort from our collaborating UK sites and the willing young people who took part. Together we have shown that mixed and fractional doses of Covid-19 vaccine schedules studied are well-tolerated and generate robust immune responses in adolescents for at least eight months.’
She added: ‘Of particular interest is the enhanced performance of Novavax’s protein sub-unit vaccine following a dose of Pfizer-BioNTech’s mRNA, compared to the standard two doses of Pfizer-BioNTech mRNA. While interpretation should be cautious considering the study’s small sample size, this suggests that a combination of vaccine platforms may result in a greater breadth of protection.’