The US pharmaceutical said on Friday that a lower dose of its COVID-19 vaccine in those aged between two and four generated a weaker immune response than expected. In the study, children were given the Pfizer vaccine in two three-microgram doses – this is around one-tenth of the jab administered to adults.
The results found it did not create the same antibody response that a larger dose of the vaccine had in older children.
The three-microgram dose also generated a similar immune response in younger children aged six to 24 months.
Pfizer had expected to produce positive vaccine data for the under-five age group by the end of year.
The company is now going to trial a three-dose course in both age groups, as well as in older children.
It found the risk of reinfection with Omicron is 5.4 times greater than the previously dominant Delta variant.
Professor Neil Ferguson from Imperial College London, whose modelling helped to trigger the first lockdown in March 2020, said the variant poses a “major threat”.
He said: “This study provides further evidence of the very substantial extent to which Omicron can evade prior immunity, given by both infection or vaccination.
“This level of immune evasion means that Omicron poses a major, imminent threat to public health.”
On Friday, the UK recorded 93,045 new Covid cases, the highest daily total since the pandemic began.
It is understood the Prime Minister is considering a two-week circuit-breaker lockdown over the Christmas period following the surge in infections.
A Government spokesperson said: “The Government will continue to look closely at all the emerging data and we’ll keep our measures under review as we learn more about this variant.”