Pfizer has selected a lower dose of its Covid-19 vaccine, co-developed with BioNTech, for assessment in Phase II/III clinical trial involving children aged under 12.

The company chose 10µg and 3µg doses of the Covid-19 vaccine based on safety, tolerability and immune response data gathered from 144 children in a Phase I trial.

In the Phase II/III trial, up to 4,500 children will be enrolled at more than 90 sites in the US, Finland, Poland and Spain.

Participants aged five to 11 years will receive a 10µg dose of the vaccine, while those aged six months to five years will receive a 3µg dose.

In a statement, Pfizer clinical research and development senior vice-president Dr Bill Gruber said: “We take a deliberate and careful approach to help us understand the safety and how well the vaccine can be tolerated in younger children.

“Children younger than 12 make up a significant portion of the total global population and can develop Covid-19 disease, and also can spread the virus to others.

“If successful, we believe vaccinating children will help further protect our communities and contribute to the evolving herd immunity.”

Results from five to 11-year-old subjects are expected to be available in September and will be used to seek emergency use authorisation. Data from children aged two to five years is set to follow soon after.

Pfizer anticipates data from participants aged six months to two years in October or November.

The company’s Covid-19 vaccine already holds emergency use authorisation for children aged 12 to 15 in the US, Europe and Canada.

This age group received a 30μg dose of the vaccine. Data demonstrated a 100% vaccine efficacy in participants with or without prior Covid-19 infection and strong antibody responses.

Last month, a Public Health England (PHE) study found that the Covid-19 vaccine was effective against the B.1.617.2 variant of SARS-CoV-2 first identified in India and now detected worldwide.