The phase III trial included data from 43,448 participants who were 16 years of age and older. Half of the participants received 30-µg BNT162b2 and half received the placebo in a two-dose regimen 21 days apart. The vaccine candidate was well-tolerated and demonstrated 95% efficacy in preventing COVID-19 in those without prior infection seven days or more after the second dose.

The results were generally consistent across subgroups defined by age, gender, race, ethnicity, baseline body mass index (BMI), or presence of other underlying comorbidities. In addition, partial protection began as early as 12 days after the first dose, the researchers found.

Among 36,523 participants who had no evidence of existing or prior SARS-CoV-2 infection, there were 170 cases of COVID-19 observed with onset at least seven days after the second dose. The researchers found eight cases occurred in vaccine recipients, and 162 in placebo recipients.

Among participants with and without evidence of prior SARS CoV-2 infection, nine cases of COVID-19 were found among vaccine recipients and 169 among placebo recipients.

Pfizer and BioNTech are planning additional studies to evaluate the vaccine in pregnant women, children younger than 12, and those in special risk groups, such as the immunocompromised.