ABSTRACT
Rapid development and deployment of vaccines is crucial to control the continuously evolving COVID-19 pandemic. The placebo-controlled phase 3 efficacy trial is still the standard for authorizing vaccines in the majority of the world. However, due to a lack of eligible participants in parts of the world, this has not always been feasible. Recently, the Taiwan Food and Drug Administration, following the consensus of the International Coalition of Medicines Regulatory Authorities (ICMRA), adopted the use of immunobridging studies as acceptable for authorizing COVID-19 vaccines in lieu of efficacy data. Here, we describe a study in which our candidate vaccine, MVC-COV1901, an adjuvanted protein subunit vaccine, has been granted emergency use authorization (EUA) in Taiwan based on a noninferiority immunobridging study. Immunogenicity results from the per protocol immunogenicity (PPI) subset (n = 903) from the MVC-COV1901 phase 2 trial were compared with results from 200 subjects who had received an adenovirus vector vaccine, AstraZeneca ChAdOx nCOV-19 (AZD1222), in a separate study. The lower bound of the 95% confidence interval (CI) of the geometric mean titer (GMT) ratio comparing MVC-COV1901 to AZD1222 was 3.4. The lower bound of the 95% CI of the sero-response rate was 95.5%. Both the GMT ratio and sero-response rate exceeded the criteria established by the Taiwan regulatory authority, leading to EUA approval of MVC-COV1901 in Taiwan.
ABSTRACT
In providing human immunity from the SARS-CoV-2 virus, AstraZeneca’s ChAdOx1 nCov-19 vaccines have been administered in multiple nations around the world. Throughout this literature review, the background behind derivation of this vaccine from chimpanzees to avoid pre-existing human immunity to this adenoviral vector’s mechanism of interactions will be discussed prior to clinical issues this vaccine brings. Arranged in sections, this discussion concerns the adenovector vaccine’s ability to induce both innate and adaptive immunity, featuring the mucosal route of administration’s ability to stimulate tissue-resident memory T cells (TRM), a crucial part of the adaptive immune system. Despite its solid ability to stimulate immunity with high efficiency and efficacy, a surge in female fatalities following administrations of the ChAdOx1 nCov-19 adenovector vaccines have also occurred. Published articles regarding both hypothesised mechanisms as well as recorded incidences of this rare vaccine-induced blood clots, also known as the Thrombosis and Thrombocytopenia Syndrome (TTS), have been discussed. Despite still lacking a causal relationship between AZ administrations in heparin-free patients and TTS incidences, all of these articles have implied the mechanisms inducing this condition arise from an induction of platelet-activating antibodies against PF4. The most plausible arisal of these antibodies is from free DNA molecules within the ChAdOx nCov-19 vaccine. Additionally, TTS draws similarities to autoimmune heparin-induced thrombocytopenia cases, where a platelet count decline also occurs. © 2018-2022, Rangsit University.