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Half-dose Pfizer COVID booster practically as efficient as full dose with fewer unintended effects

In a latest research revealed in The Lancet Regional Well being Western Pacific, researchers examine the immunogenicity, reactogenicity, and security of a half-dose Pfizer-BioNTech BNT162b2 coronavirus illness 2019 (COVID-19) booster to a full-dose in adults beforehand vaccinated with ChAdOx1 (ChAd), BBIBP-CorV (BBIBP), or Gam-COVID-Vac.

Study: Immunogenicity, safety, and reactogenicity of a half- versus full-dose BNT162b2 (Pfizer-BioNTech) booster following a two-dose ChAdOx1 nCoV-19, BBIBP-CorV, or Gam-COVID-Vac priming schedule in Mongolia: a randomised, controlled, non-inferiority trial. Image Credit: wavebreakmedia / Shutterstock.com Research: Immunogenicity, security, and reactogenicity of a half- versus full-dose BNT162b2 (Pfizer-BioNTech) booster following a two-dose ChAdOx1 nCoV-19, BBIBP-CorV, or Gam-COVID-Vac priming schedule in Mongolia: a randomised, managed, non-inferiority trial. Picture Credit score: wavebreakmedia / Shutterstock.com


As COVID-19 vaccine effectiveness diminishes over time as a result of waning immunity and rising viral variants, booster doses have develop into essential, notably for extremely susceptible affected person populations. Nations are more and more administering third and fourth booster photographs, usually utilizing the BNT162b2 vaccine.

Heterologous boosting with BNT162b2 has proven greater immunogenicity however better reactogenicity as in comparison with homologous boosting in people initially vaccinated with vaccines like ChAd, BBIBP, or CoronaVac. Fractional dosing, a method used efficiently in different ailments, is being thought-about for reinforcing, given its potential to cut back reactogenicity and prices, in addition to enhance vaccine acceptance and resilience towards provide disruptions.

Nonetheless, information is proscribed on the effectiveness and reactogenicity of fractional BNT booster doses in various populations, particularly these vaccinated with vaccines like BBIBP or Gam-COVID-Vac, that are generally utilized in low- and middle-income nations; due to this fact, additional analysis is important.

Concerning the research 

The newest part III research carried out in Mongolia examined the results of a half-dose (15 μg) versus a full-dose (30 μg) of the BNT162b2 COVID-19 booster vaccine in adults beforehand immunized with two doses of both ChAd, BBIBP, or Gam-COVID-Vac. This research was ethically authorised and sought to watch topics for one 12 months, concentrating on the preliminary 28-day interval.

Adults who had taken their first dose of vaccines for greater than six months in numerous well being facilities and organizations had been included within the present research. For inclusion standards, all research individuals provided written knowledgeable consent.

Stratified in keeping with the vaccine kind and participant’s age, sufferers had been randomly distributed into half- or full-dose teams. Contributors and people answerable for evaluating reactogenicity remained unaware of group assignments till day 28.

A baseline evaluation was carried out for every participant, adopted by the gathering of blood samples, after which individuals had been administered their respective booster doses. Research individuals had been noticed for quick reactions and had been supplied with devices to watch reactogenicity over a interval of 1 week. Blood samples and well being assessments had been subsequently carried out on days one, seven, and 28.

The first outcomes of the investigation included seroresponse fee and reactogenicity inside 28 days after boosting. Seroresponses had been decided primarily based on particular anti-spike immunoglobulin G (IgG) ranges, whereas reactogenicity was assessed by the severity of reactions. Secondary endpoints included the comparability of geometric technique of antibody ranges, and any reported hostile results.

Statistical evaluation, carried out utilizing the Estimand Framework, thought-about each major and secondary endpoints, with changes for varied covariates, and was carried out utilizing Stata software program.

Research findings 

Between Might and September 2022, 300 individuals obtained a full 30 µg dose, and 301 obtained a half 15 µg booster dose. The median age of the research cohort was 44 years, with about 40% exceeding at the least 50 years of age, which is consultant of the Mongolian inhabitants. The median interval between the second and third doses was 428 days.

People who obtained the half-dose reported fewer native and systemic reactions as in comparison with the full-dose group. Particularly, there have been fewer instances of ache, tenderness, fever, vomiting, diarrhea, headache, fatigue, joint ache, and muscle ache. Grade three and 4 reactions inside seven days following vaccination had been low in each teams.

By way of immunogenicity, 84.7% and 86.6% of the half-dose and full-dose recipients exhibited a seroresponse, respectively. The proportion distinction in seroresponse between the half- and full-dose teams was throughout the acceptable vary, thus indicating non-inferiority. Nonetheless, the response was barely decrease within the half-dose group amongst Gam-primed individuals.

The geometric imply ratio (GMR) of day 28 anti-spike IgG ranges between the half- and full-dose teams was 0.94 total. This was related for ChAd- and BBIBP-primed individuals however decrease for Gam-primed individuals within the half-dose arm. This sample endured throughout totally different age and physique mass index (BMI) teams.

Exploratory evaluation confirmed a better response to the booster dose in people with decrease baseline IgG ranges, which was particularly pronounced in Gam-primed half-dose recipients. Neutralizing antibody ranges towards the Wuhan-Hu-1 viral variant had been excessive pre- and post-boosting in each dose teams and throughout all priming schedules. An identical enhance was noticed for neutralizing antibodies towards the Omicron B.1.1.529 variant after boosting.

Antagonistic occasions (AEs) and critical hostile occasions (SAEs) had been comparable throughout each teams, with not one of the SAEs associated to the research vaccine. There have been no variations within the frequency, severity, or length of AEs between the research arms.

Journal reference:

  • Batmunkh, T., Moore, Ok. A., Thomson, H., et al. (2023). Immunogenicity, security, and reactogenicity of a half- versus full-dose BNT162b2 (Pfizer-BioNTech) booster following a two-dose ChAdOx1 nCoV-19, BBIBP-CorV, or Gam-COVID-Vac priming schedule in Mongolia: a randomised, managed, non-inferiority trial. The Lancet Regional Well being Western Pacific. doi:10.1016/j.lanwpc.2023.100953 

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