COVID-19 Vaccines: What Does the Evidence Say about Delaying the Second Dose ?

Debate continues around whether delaying second COVID-19 vaccine doses is a reasonable strategy amid global supply shortages. Several governments and advisory bodies have extended the interval between doses to increase first-dose coverage, hoping to curb transmission and ease pressure on strained health systems. Early trial data suggest one dose of Pfizer, Moderna, or AstraZeneca offers meaningful short-term protection, but evidence on durability and long-term efficacy with delayed boosting is limited. Concerns also persist about fostering partially immune populations that could encourage vaccine-resistant variants and reduce public confidence. With modelling studies hinting at potential population-level benefits, the balance between urgency, safety, and scientific certainty remains unsettled, underscoring the need for stronger empirical data.