The researchers said that fourth doses of coronavirus jabs have been offered as a spring booster for those most vulnerable in Britain. This has been a precautionary strategy to maintain high levels of immunity prior to the study data being available, they added.
The study, published in The Lancet Infectious Disease journal, show that a fourth dose mRNA booster vaccines for the virus are well-tolerated in those who received Pfizer as a third shot.
The researchers said that they are also effective at increasing both antibody and cellular immunity up to and above baseline and peak levels observed following third dose boosters.
Professor Saul Faust, trial lead and Director of the NIHR Southampton Clinical Research Facility, stated, "These results underline the benefits of the most vulnerable people receiving current spring boosters and gives confidence for any prospective autumn booster programme in the UK, if the Joint Committee on Vaccination and Immunisation considers it needed at that time.".
In the findings, nearly 166 people who had received a third dose of Pfizer, after Pfizer or AstraZeneca initial doses in June last year, were randomised to receive full dose Pfizer or half dose Moderna as a fourth shot.
The fourth jab was administered approximately seven months after the third shot.
While pain at Covid-19 vaccination site and fatigue were the most common side effects, there were no vaccine-related serious adverse events and fourth doses were safe and well tolerated, the researchers added.
"We knew that it was important to offer a fourth dose to those most vulnerable earlier in the year," Professor Andrew Ustianowski, NIHR Clinical Lead for the COVID-19 Vaccination Programme, stated.
"These new study findings support that decision and provides the public with the confidence that fourth doses are both safe and even more effective than third doses at boosting immunity against COVID-19," Ustianowski added.
