A Phase II clinical trial, called Com-COV3, led by the University of Oxford has expanded to assess mixed Covid-19 vaccine dose schedules in adolescents aged 12 to 16 years in the UK.

The trial is funded by the UK Vaccines Taskforce (VTF) and the National Institute for Health Research (NIHR).

In the expanded portion, the trial will test the Covid-19 vaccines of Pfizer-BioNTech, Novavax and Moderna as combination regimens to potentially offer immune protection against the disease in a minimum of 360 adolescents.

Participants will be given a first dose of the Pfizer-BioNTech vaccine and then either a full dose or half dose of the Pfizer shot, a full dose of Novavax’s vaccine candidate or a half dose of Moderna’s vaccine at least eight weeks later.

The objective is to compare the immune responses from a heterologous schedule to those from a homologous regimen.

Subjects will be followed up to check for safety and immune responses, with results to be reported in a few months.

Trial lead researcher Matthew Snape said that the primary concern is the risks of myocarditis, especially with the second Pfizer vaccine dose in young men, Reuters reported.

Novavax Research and Development president Gregory Glenn said: “Expanding our understanding of how different Covid-19 vaccines can be used to implement flexible vaccine programmes across all age groups will be vital to ultimately controlling the pandemic.

“A mixed vaccination series could offer the potential to maximise the use of existing vaccine supply, increase the total number of individuals who can ultimately be vaccinated and accelerate rapid and equitable access across the globe.”

The company’s Covid-19 vaccine candidate, NVX-CoV2373, is also one of the four anti-SARS-CoV-2 vaccines being assessed in the University of Oxford-led Com-COV2 trial.

Com-COV2 is designed to study mixed Covid-19 vaccine regimens in 1050 adults aged 50 years or above. Other vaccines included in the trial are of Oxford-AstraZeneca, Pfizer and Moderna.