Fourth Covid-19 jabs give people protection “over and above” that afforded to people who have had three jabs, a new study suggests.
Research is continuing to assess the levels of protection people have after vaccination, and for the length of time that this protection lasts.
A team of academics led by the University of Southampton have been tracking a group of people and their levels of antibodies and T cells, both measures which indicate a person’s level of protection against a virus.
The CovBoost trial also examined side-effects after a fourth jab.
Some 166 people took part in the study and offered blood samples, which means that scientists could examine the concentration of antibodies in the blood.
These were examined at various time points, including 28 days after the third jab was given; again just before their fourth boost was administered – which took place, on average, just over 200 days later; and then 14 days after they had their fourth jab.
The levels of antibodies waned in the period between third jabs and fourth boosters.
But a fortnight after the booster jab antibody levels rose even higher than the levels seen after the third jab.
And there were significant boosts compared with the levels seen on the day they were given their fourth booster – participants had 12 to 16 times higher levels of antibodies in the blood a fortnight after they got their fourth shot, compared with the day it was delivered.
Boosts were also seen in the cellular level, according to the study, which has been published in The Lancet Infectious Diseases journal.
Researchers examined data on people who had two doses of the AstraZeneca jab, followed by a Pfizer booster, who then received either a Pfizer jab or half dose of a Moderna jab for their fourth vaccine.
They also looked at people who had three doses of Pfizer, followed by a fourth Pfizer shot or a half-dose Moderna jab.
No severe side-effects were recorded among participants, with some reporting pain or fatigue.
But the authors said that the study provided a “hint” that a small number of people might reach a “ceiling” in terms of the amount of protection that they could get from a fourth jab.
The authors said that some people had high levels of immune response “even before the fourth dose and had limited boosting from the fourth dose”, including people who had just been infected with the virus.
Trial lead Professor Saul Faust, 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.”
Health and Social Care Secretary Sajid Javid added: “This is further evidence underlining the importance of people coming forward for their booster as soon as they are eligible.
“We’re able to live with Covid thanks to the protection provided by our phenomenal vaccine programme and a booster dose will top up your immunity to continue to keep you and your loved ones safe.”
A number of groups have been called forward for a spring booster, including to those aged 75 and over, people who live in care homes for older people, or people aged 12 and over who have a weakened immune system.
For most this will have been a fourth vaccine dose, but for some with a weakened immune system it will have been their fifth.
The new study supports the booster campaign and will also be used by experts who will decide on the future of the vaccination programme – including whether or not people with weakened immune systems should have further jabs and whether or not the booster programme should be rolled out to include other groups.
So far more than three million people have received their spring booster in England alone, according to the NHS in England.