Immunogenicity and clinical features relating to BNT162b2 messenger RNA COVID-19 vaccine, Ad26.COV2.S and ChAdOx1 adenoviral vector COVID-19 vaccines: a systematic review of non-interventional studies.

Background: Vaccination against Coronavirus disease 2019 (COVID-19) is an important means of controlling the pandemic, however they are expected to stimulate immune responses when administered to confer immunity. In this review, we evaluated the clinical and laboratory features associated with BNT162b2 messenger RNA COVID-19 vaccine, Ad26.COV2.S and ChAdOx1 adenoviral vector COVID-19 vaccines, to determine their immunogenicity. Demographic distribution of pathogenic autoimmune response and time interval between vaccination and onset of symptoms were also assessed. This was to identify; persons at risk of developing auto-immune reactions and  markers to enhanced occurrence of this event. Main body: Using relevant keywords, search was conducted in the databases of PubMed, Scopus, Web of Science and Google scholar from November 2020 to May 31, 2021. Additional article was also identified through hand-searching of reference lists, and the review was conducted in line with Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines 2009. Study outcome measures were presence of antibodies after vaccination and evidence of autoimmune reactions, therefore studies relating these measures were considered eligible for this review. Studies showed stimulation of immune response with administration of BNT162b2 mRNA vaccine, ChAdOx1 and Ad26.COV2-S adenovirus vector-based vaccines. Aside SARS-CoV-2 spike protein antibodies, elevated D-dimers, presence of PF4 and low fibrinogen were most commonly seen laboratory features in persons with autoimmune reactions following vaccination. In addition, thrombotic thrombocytopenia was the commonest clinical features observed with ChAdOx1 and Ad26.COV2-S adenovirus vector-based vaccines. Findings from this study also suggest higher susceptibility of women of 22-60 years to the pathogenic immunogenicity that may particular result from exposure to ChAdOx1 and Ad26.COV2-S adenovirus vector-based vaccines. Time interval of 4-37 days was mostly observed between vaccination and occurrence of a symptom. Conclusion: Immune thrombotic thrombocytopenia and other PF4 dependent syndrome are likely associated with ChAdOx1 and Ad26.COV2.S adenovirus vector vaccines, mostly occurring in women usually within 4-37 days of first dose of vaccine. Enhanced knowledge about vaccine adverse effects and its distribution is crucial for effective vaccination strategies.