Pfizer Inc and its German partner BioNTech announced on Thursday that findings from a Phase III trial showed that a booster dose of its COVID-19 vaccine, including the Delta form, had high efficacy against the virus.

During a period when the Delta strain was widespread, they said a trial of 10,000 persons aged 16 and over showed 95.6 %efficiency against the infections.

The booster shot also had a favorable safety profile, according to the study.

Pfizer has previously stated that the efficiency of their two-shot vaccination decreases over time, citing research that found 84 % effectiveness four months after the second treatment, down from a peak of 96 %. Some governments have already begun preparing to administer booster dosages.

Pfizer, BioNTech say vaccine protects for 6 months

The study's median period between the second dose and the booster shot or placebo was roughly 11 months, according to the drugmakers, who also noted that the booster group had just five cases of COVID-19 compared to 109 cases in the placebo group.

Pfizer CEO Albert Bourla said in a statement, "These results provide further evidence of the benefits of boosters as we aim to keep people well-protected against this disease,"

The participants' average age was 53 years, with 55.5 % being between 16 and 55 years old and 23.3% being 65 or older.

The businesses said they would submit full study results to the US Food and Drug Administration (FDA), the European Medicines Agency, and other regulatory bodies as soon as feasible for peer-reviewed publication.

For patients with impaired immune systems who are anticipated to have less protection from the two-dose regimens, US and EU regulators have previously approved a third dosage of COVID-19 vaccines from Pfizer-BioNTech and Moderna.