The winding 12-month journey of the AstraZeneca COVID-19 vaccine since its first administration to humans.

The deficiently designed and conducted initial clinical development plan and the occurrence of thrombotic thrombocytopenia cases, have marked the first 12-month journey of the AstraZeneca coronavirus disease 2019 (COVID-19) vaccine after it was first administered to humans. When it was authorized, there were no available efficacy data in the elderly. However, this age group was included in the product labelling based on immunogenicity data. The lack of safety and efficacy data in the elderly that was acknowledged in the product information, triggered most European Union (EU) countries to limit the administration of this vaccine to certain age groups. In February-March/2021, after the results of observational studies supported the vaccine effectiveness in the elderly, several countries broadened its use to this age group. When trust on the vaccine was ramping up, unusual blood clot cases were described in Europe, which led 24 countries around the world to temporarily halt its administration. These cases were first described as thrombotic thrombocytopenia in late March. In mid-April, the UK Medicines and Healthcare products Regulatory Agency (MHRA) and the European Medicines Agency (EMA) updated the product information and confirmed the positive benefit/risk ratio of the vaccine, recommending its use with no age restrictions. The World Health Organization (WHO) coincided with this approach. However, several countries decided to limit its use to certain age groups. The EMA listed thrombotic thrombocytopenia as a "very rare" adverse reaction. Although, the AstraZeneca vaccine was conceived in early 2020 to be a worldwide leader in the fight against COVID-19, its use was abandoned by the African Union, Denmark, and Israel. However, this vaccine has shown its usefulness in many settings across the world.