Facing the unprecedented COVID-19 pandemic, decision-makers often act swiftly and make quick decisions to employ public health measures to contain and control the pandemic, even if there is a lack of solid evidence to support the effectiveness and safety of these measures, exemplified by the controversial delaying-the-second-dose and mix-and-match (formally known as heterologous prime-boost) vaccination strategies. In early 2021, just days after countries like the United Kingdom (UK) announced their policy to delay giving the second dose of COVID-19 vaccine, an OE Original (COVID-19 Vaccines: What Does the Evidence Say about Delaying the Second Dose?) examined available evidence at the time and found....