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COVID-19 vaccine boosters give immunity three months on

Third doses of several COVID-19 vaccines give prolonged protection against the infection, according to the NIHR-supported COV-BOOST study.

Strong immune responses were seen 84 days after third jabs of five of the vaccines currently approved for UK use: AstraZeneca, Pfizer, Moderna, Janssen and Novavax. 

Of 2,883 participants, including 187 vaccinated at the Churchill Hospital, Oxfordshire, 2,422 had not caught the infection by their three-month follow-up. 

Third doses of Pfizer or Moderna vaccines produced the strongest immunity for participants given two initial doses of AstraZeneca, while a third dose of the Janssen jab gave better protection than Pfizer or Moderna following two Pfizer doses.

Responses to a half or full dose of Pfizer were similar in participants who had AstraZeneca or Pfizer doses initially.

The rate at which immune cell responses declined after third doses was similar between all vaccine combinations and doses.

These findings follow initial results published last year on the safety and effectiveness of third doses after 28 days, which underpinned the UK’s autumn 2021 booster roll-out.

Saul Faust, trial lead, said: “What COV-BOOST has shown is that most of the currently approved vaccines drive persistent protection when used as a third dose. That gives countries worldwide confidence in the value of booster programmes and flexibility in delivering them.

“Although very high antibody levels may be useful to control a new variant spreading in society in the first few weeks after a booster jab, the longer-term protection against hospitalisation and death is perhaps the most important factor for future booster programmes.

“We also found a half dose of the Pfizer vaccine gives similar responses as a full dose at three months, which could help in planning global vaccine supply and delivery.”

The seven vaccines trialled in the main COV-BOOST trial were:

  • AstraZeneca (Oxford-AstraZeneca)
  • Pfizer (Pfizer-BioNTech)
  • Moderna
  • Novavax
  • Valneva
  • Janssen
  • CureVac (first-generation vaccine no longer in clinical development)

Ongoing COV-BOOST sub-studies are investigating the interval between second and third doses, an Omicron variant vaccine and fractional dosing in young people aged 18-30 years. Find out more on the study website

Read more on the NIHR website.