Fourth Covid jab can give higher immunity than initial booster, study finds

A fourth dose of a Covid vaccine can increase the body's immune defences beyond the peak achieved after a third dose, according to research.

People over the age of 75, people living in care homes for older people, and people over the age of 12 who are immune to the vaccine are all offered a second booster.

Researchers say a fourth dose can help the immune system recover after a third jab.

Prof Saul Faust, who led the study, said that a fourth dose of Covid-19 vaccine can give a substantial boost to the immune system.

166 participants in the UK-based Cov-Boost trial received a fourth Covid jab on average seven months after having had a Pfizer/BioNTech jab as their third dose, according to a report in the Lancet Infectious Diseases. The Pfizer/BioNTech jab and the Oxford/AstraZeneca vaccine were the first two to be given to participants.

Half of them were given a full dose of the Pfizer/BioNTech Covid jab, while the other half were given half a dose of the Moderna jab. There were no serious adverse events associated with the vaccines.

The team found that 14 days after receiving the fourth jab, there was a 1.6-fold increase in antibodies among those who received the Pfizer/BioNTech vaccine, and a more than twofold increase among those who received the half-dose Moderna jab.

Those over and below 70 years of age saw increases.

Between the day before the fourth vaccine and 14 days after, levels of T-cells increased significantly.

The results for immunogenicity are consistent with the little observational evidence on vaccine effectiveness available from Israel, which indicates increased protection against disease from a fourth dose booster.

Faust said that those who had little waning of their immune responses before their fourth dose gained only a limited increase in their immune responses as a result of the booster, with similar findings for others who had a recent history of a Covid infection.

Faust said it was up to the UK's Joint Committee on Vaccination and Immunisation to decide if a second booster should be offered more widely.

Some experts think that people who are yet to reach middle age might never be offered another Covid jab.

Prof Danny Altmann said that the new study showed the added value of a fourth dose and that Omicron still posed a serious threat.

It doesn't suggest we should give up and have no more boosters because our first-generation vaccines are no longer effective.

Many of us, even with high apparent antibody levels, actually show very little protective neutralisation of Omicron.