A clinical study to assess antibody level of standard dose versus fractional doses of COVID-19 vaccine (PFIZER-BIONTECH)

Abstract

Background: Additional or booster doses of Covid-19 vaccines are now used in most countries although data remain insufÏcient regarding optimal timing, target groups, duration of protection and safety. An additional dose of the vaccine against the covid-19 infection (SARS-CoV-2) boosts the immunity of the priming vaccine and to prevent the new emerging variants and severe illnesses. In addition, the fractional dose (Pfizer-BioNtech) booster shown to be equally effective, cost beneficial and improve access to the resource limited settings. Study immunogenicity as well as safety and reactogenicity of standard dose versus fractional doses of COVID-19 vaccine (Pfizer-BioNTech) given as a booster dose after priming with Sinopharm, AstraZeneca or Sputnik is carried in 3 countries including Mongolia, Australia and Indonesia. Aim: To assess the immune response measured as binding antibodies (IgG ELISA) following standard versus fractional doses of Pfizer vaccine given as a booster dose after primed with Sinopharm. Materials and Methods: The study is randomised, non-inferiority phase 3 trial comparing the immunogenicity, safety and reactogenicity of a BNT half-dose (15 μg) versus BNT full-dose (30 μg) doses of the Pfizer vaccine to levels Euroimmun S1 IgG ELISA was used to compare 2 tests before and 28 days after vaccination. This clinical trial is a single blinded, 1:1 randomized controlled study to assess Binding antibody by using Euroimmun S1 IgG ELISA following booster doses of SARS-CoV-2 vaccines both standard (30μg) and fractional doses (15μg) in adults. The research was started at the meeting of the research ethics control committee of MNUMS on September 23, 2022 (No. 3-08). Results: The 401 participants who met the criteria for the study were consented and 399 participants were participated in the study. Post-vaccination response rates were similar after fractional and standard dose vaccines, but the rates of severe reactions and systemic reactions (4/299 [1.3%] and 6/299 [2.0%]), respectively, were less pronounced in fractional dose participants (60%, 72% and 25%, 32%). Antibody level was similar in both groups. Seroresponse was 84.7% (250/295) and 86.6% (253/292) in the half-dose and full dose arms, respectively (Difference: −2.8%; 95% CI −7.7, 2.1) which was statistically significant. Conclusions: Therefore, Pfizer (Pfizer-BioNtech) half-dose vaccine elicits a similar immune response with fewer reactions, showing that Pfizer half-dose vaccine after Sinopharm vaccine is effective. As lowand middle-income countries where the Sinopharm (BBIBP-CorV®) vaccine is widely used and fractional dose regime can reduce the cost per dose.