Booster shot of Pfizer Covid jab increases protection to over 90%, new study finds

A booster shot of the Pfizer vaccine gives over 90% protection against symptomatic Covid-19 regardless of which vaccine was used first, a British study has found.

The study, led by the UK Health Security Agency and published on Monday, examined the effectiveness of this booster for over-50s who had received AstraZeneca or Pfizer as their first shots.

“Our study provides real world evidence of significant increased protection from the booster vaccine dose against symptomatic disease in those aged over 50 year of age irrespective of which primary course was received,” the study found.

The study found in people who had received the AstraZeneca vaccine, the absolute vaccine effectiveness was boosted to 93.1%.

For people whose first jabs were Pfizer, the vaccine effectiveness was increased to 94%.

This contrasts with the vaccine effectiveness measured for people who were five months on from their original shots but who had not received a booster. The vaccine effectiveness in these cases was measured at 44.1% for people who had AstraZeneca and 62% for those who had Pfizer.

The study notes protection against severe disease and hospitalisation remained strong for people after the original two doses, but there is now concern around waning immunity “in older adults and those with underlying medical conditions compared to young, healthy adults”.

The booster campaign started in the UK on September 21 for older people, and on Monday was expanded to include all over-40s. It was also decided to offer teens aged 16 to 17 a second dose of the Pfizer vaccine as until now one dose had been deemed sufficient.

In Ireland, it is expected boosters will be rolled out for all adults aged over 50 after Cabinet meets on Tuesday.

“These findings suggest that the booster offers very high levels of protection against symptomatic disease, at least in the short-term,” the study states.

“Given the recent deployment of the booster programme in the UK, further follow-up is needed to understand how protection changes over time against both mild and severe disease.” The authors state the findings indicate greater protection for vulnerable older people if they receive a booster shot.

“This will be important in the 2021to 2022 winter period when Covid-19 is likely to co-circulate alongside other respiratory viruses, including seasonal influenza virus,” the study states.