A booster shot of the anti-Covid-19 vaccine developed by Pfizer/BioNTech is 95.6 per cent effective against symptomatic infection, according to trial data published by the makers.

The clinical phase three trial with “10,000 participants 16 years of age and older” showed “a relative vaccine efficacy of 95.6pc against disease during a period when Delta was the prevalent strain”, the companies said in a statement.

The study presented the “first results” of a booster trial, with a third shot of the vaccine demonstrating a “favourable safety profile”.

“These results provide further evidence of the benefits of boosters as we aim to keep people well-protected against this disease,” said Pfizer CEO Albert Bourla.