An analysis of data from four AZ trials (NCT04324606, NCT04400838, NCT04444674, ISRCTN89951424) included 17,177 patients, with 332 developing COVID-19. The analysis found overall efficacy to be 66.7% two weeks or more after the second dose. Vaccine efficacy was 63.1% in patients that received two full doses of the vaccine and 80.7% in patients that received a half dose initially, followed by a full dose for the booster. Exploratory endpoints included efficacy with different dosing intervals. Patients that received a second dose of vaccine at 12-weeks or later had antibody titers 2-fold higher with 81.3% efficacy. Efficacy was 55.1% in patients whose interval between doses was less than six weeks. A single dose of the vaccine demonstrated efficacy of 76% for 90 days in the prevention of symptomatic infection but did not offer protection for asymptomatic infection.
A retrospective analysis by Israeli researchers found the Pfizer-BioNTech vaccine to reduce COVID-19 infection by 30% and symptomatic infections by 47% during the first two weeks after the initial vaccination. In days 15-28 after the immunization, all COVID-19 infections are reduced by 75% and symptomatic infections by 85%.
A preprint draft, describes a small trial, where patients that had recovered from COVID-19 had a robust increase in antibody titers after the first dose, but a small increase after a second dose. Patients that had not been infected with COVID-19, had a robust increase with both doses.
A preprint draft describes how a single dose of either the Pfizer-BioNTech or Moderna vaccine given to patients that recovered from COVID-19 resulted in high levels of antibodies that were effective in neutralizing the B.1.351 (South African) variant. Without the boost in immunity from the vaccine, the patients’ antibody levels were not robust enough to neutralize the variant.
Anthony Fauci and Andy Slavitt have stated, the small studies supporting a single vaccine dose are too limited to change The U.S. recommendation for two doses of either vaccine.
The CDC analyzed the safety data of the Pfizer-BioNTech or Moderna vaccines after 13,794,904 vaccine doses were given. The incidence of adverse events was 0.05% with the most common being headache, fatigue, and dizziness. Only 9.2% of adverse events were considered serious. The overall rate of anaphylaxis was similar to other vaccines with 4.5 events per million doses.
Sanofi and GlaxoSmithKline are initiating a 720 patient, Phase II study (NCT04762680) with a reformulated version of their COVID19 vaccine. A positive trial would lead to a Phase III vaccine in 2Q21.