The third dose of Pfizer-BioNTech vaccine against Covid-19 virus has shown 95.6% efficacy compared to those who did not receive a booster, according to the vaccine makers.
Pfizer-BioNTech announced the results from a Phase 3 trial evaluating the efficacy and safety of a 30-µg booster dose, the same dosage strength as those in the primary series, of the mRNA-based Pfizer-BioNTech Covid-19 vaccine.
The clinical phase three trial with "10,000 participants 16 years of age and older" showed "a relative vaccine efficacy of 95.6 per cent 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".
Citing multiple subgroup analyses, the study suggests that booster dose efficacy was consistent irrespective of age, sex, race, ethnicity, or comorbid conditions.
The US and German partners are the first to publish efficacy results from any randomized, controlled Covid-19 vaccine booster trial.
Pfizer-BioNTech and Moderna Covid vaccines are at the centre of the immunisation programme in the United States to fight the pandemic.
The US Food and Drug Administration (FDA) has already authorised the third dose of Pfizer Covid vaccine for emergency use among individuals 65 years of age and older, all adults at high risk of severe Covid-19, and those with frequent institutional or occupational exposure to the virus.
The European Medicines Agency (EMA) approved a booster for over-18s at the beginning of October, allowing national regulators to decide which groups should be eligible first.