Fourth Covid jab gives bigger boost than third dose

The latest results from the COV-BOOST (opens in a new tab) trial, run at NIHR Cambridge Clinical Research Facility at Cambridge University Hospitals NHS Foundation Trust (CUH), show that a fourth dose mRNA vaccine is safe and boosts antibody levels higher than that of a third dose.

Researchers have published their findings today in The Lancet Infectious Diseases (opens in a new tab).

Fourth doses of Covid vaccines have been offered as a spring booster for those most vulnerable in the UK.

This has been a precautionary strategy (opens in a new tab) to maintain high levels of immunity prior to COV-BOOST study data being available.

Professor Krishna Chatterjee, Director of the NIHR Clinical Research Facility in Cambridge, who is leading the trial at CUH, said:

“Our teams continue to work tirelessly to find vaccines and treatments to protect against Covid-19 and the results of the COV-BOOST study are testament to this.

"We couldn’t do it without the 230 local people who volunteered to take part in all phases of this trial either, and we thank them, along with all who are involved in ongoing research to tackle the virus as the pandemic evolves.”

The latest findings show that fourth dose mRNA booster vaccines for Covid are well-tolerated in people who received Pfizer as a third dose.

They are also effective at increasing both antibody and cellular immunity up to and above baseline and peak levels observed following third dose boosters.

While pain at 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 two vaccines trialled in the fourth dose sub-study were those deployed in the UK NHS third dose booster campaign:

● Pfizer (Pfizer-BioNTech)

● Moderna (half dose – 50 micrograms)

Professor Saul Faust, trial lead and Director of the NIHR Southampton Clinical Research Facility, said:

“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.”

The COV-BOOST study, led by University Hospital Southampton, provided the world’s first data (opens in a new tab) on the safety, immune responses and side-effects of a third Covid vaccine dose in mix and match schedules.

The study was key to shaping the UK’s autumn booster programme and provides vital evidence for global vaccination efforts.

Professor Andrew Ustianowski, NIHR Clinical Lead for the COVID-19 Vaccination Programme and Joint National Infection Specialty Lead said:

"The COV-BOOST study has continuously supported the UK's booster vaccination programme and had further impact on how vaccines are administered globally. The study's latest results once again show the importance of sustained research into Covid vaccines and how they are best used to keep the virus at bay.

“We knew that it was important to offer a fourth dose to those most vulnerable earlier in the year. 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 3rd doses at boosting immunity against Covid.

"It is thanks to the endless efforts and contribution of study participants and staff across the UK that we can keep discovering more about the use of vaccines, and they continue to play a pivotal role just as they have done throughout the pandemic."

Current COV-BOOST sub-studies are investigating the interval between second and third doses, fourth doses of mRNA vaccines, an omicron variant vaccine and fractional dosing in young people aged 18-30 years (opens in a new tab).