Fact file

Which Covid vaccine works best as a booster?

Fourth jabs should only be offered to ‘most vulnerable’, UK vaccine chief says

Fourth Covid-19 vaccine boosters should not be rolled out to everyone in the UK until there is more evidence collected about their ability to stem infections, the head of the government’s vaccine advisory board has said.

Professor Andrew Pollard, chair of the Joint Committee on Vaccination and Immunisation, told The Telegraph that giving boosters to people every six months was “not sustainable” and said further vaccines should “target the vulnerable”.

“More data are needed to assess whether, when and how often those who are vulnerable will need additional doses,” he said, adding that Britain should not follow Israel and Germany’s lead by approving a fourth jab for all over-60s. 

“We can’t vaccinate the planet every four to six months,” he said. “It’s not sustainable or affordable.”

More than 34m people have received a booster dose in the UK, which equates to 59.5% of the population. 

A study of seven different vaccines, published in The Lancet last month, found the Pfizer and Moderna jabs to be the most “potent” boosters. But the emergence of the Omicron variant has complicated the picture.

Pfizer booster

In a hugely positive development, researchers in Israel found that a three-shot course of the Pfizer vaccine provides a significant defence against the new Omicron variant.

Gili Regev-Yochay, director of the Infectious Diseases Unit at the Sheba Medical Center, told Reuters a booster dose of the Pfizer jab increases protection “about a hundred fold”.

In a previous study published in The Lancet, those who received two doses of AstraZeneca and then received a booster Pfizer jab had a 25-fold increase in antibodies. When the Pfizer booster was given following two Pfizer shots, antibody levels rose more than eightfold.

The Lancet’s findings also suggest that a half dose of Pfizer “could have an effective response as a booster” and could “help with vaccine supplies”, reported The Washington Post.

In October, the first full trial of the jab’s booster efficacy found that a third dose of the Pfizer Covid-19 vaccine provides “excellent” immunity against the virus.

The pharmaceutical giant found that a booster shot of the vaccine is 95.6% more effective than two shots and a placebo at preventing infection. A researcher involved in the trial told the Financial Times (FT) that it represents a “big step forwards”.

The findings came before the recent discovery of the Omicron variant, but Danny Altmann, professor of Immunology at Imperial College London, said: “If you’ve got a glimmer of evidence, and I think we have, that the vaccines are still holding up to some extent, then it would be a good idea to get as many people boosted as quickly as possible to raise their level of protection.”

That now appears to have been vindicated by the real-world Omicron data from the Israeli study.

Moderna booster

In another encouraging development, Moderna has announced that latest clinical trials show its vaccine “significantly raises the level of antibodies that can thwart the Omicron variant”, The New York Times (NYT) said.

Results published by the company last month show that the currently authorised booster dose of 50 micrograms — half the dose given for first and second jabs — increases the level of antibodies to 37 times their former level.

A full dose of 100 micrograms was even more effective, boosting antibody levels by around 83-times compared with receiving just two jabs, Moderna said.

The results “are based on laboratory tests that do not capture the full range of the body’s immune response against the virus”, the NYT said, and suggest that “although vaccines may not prevent infection from the variant”, they will “prevent severe illness”.

The trial is now being reviewed by independent experts.

In an earlier study, a full dose of the Moderna vaccine was found to raise antibody levels 32-fold in people who had been given two initial doses of AstraZeneca.

Antibodies were raised 11-fold in those who had initially received two doses of Pfizer. Overall, it was found to be the booster that most dramatically strengthened the body’s immune defences. 

The results of the trial prompted the UK to secure an extra 114 million doses of Pfizer and Moderna vaccines to be delivered over the next two years, reported the BBC.

AstraZeneca booster

A report by the UK Health Security Agency in December suggested that people “who have had two doses of the Oxford/AstraZeneca jab 25 or more weeks ago have far lower protection against symptomatic infection with Omicron than with Delta”, reported The Guardian.

A previous study suggested that although the AstraZeneca booster did increase immune responses in people who had received two previous doses of the UK-produced jab, the level of protection was not as high as that from the Modern and Pfizer booster jabs.

But AstraZeneca announced last month that “together with Oxford university, we have taken preliminary steps in producing an Omicron variant vaccine, in case it is needed, and will be informed by emerging data”.

The company’s vaccines are not being widely used during the UK’s booster campaign. Concerns remain about the potential side effects of the jab, with research ongoing about links with rare blood clotting.

However, the NHS has said that “some people may be offered a booster dose of the Oxford/AstraZeneca vaccine if they cannot have the Pfizer/BioNTech or Moderna vaccine”.

Johnson & Johnson booster

The vaccine produced by pharmaceutical giant Johnson & Johnson is unusual in that it is a single-shot jab. In the US, a second J&J shot has been approved as a booster.

A booster shot provides high levels of protection against the Omicron variant, according to data from a trial of healthcare workers in South Africa released in late December.

Preliminary results from the study, which has not been peer-reviewed, found that for people who had received one dose of the US-developed vaccine, the booster improved protection against hospitalisation to 85% from 63%.

Results of a trial published in September found that protection against moderate to severe disease in people given a second J&J vaccine between two and six months after their first rose from 85% to 94%.

Their amount of neutralizing antibodies also increased four-fold, explained Maureen Ferran, associate professor of biology at Rochester Institute of Technology, for The Conversation.

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