The Importance of a Timely Second Dose of the 2021 COVID-19 mRNA Vaccine Depends on the Protection Afforded by a First Dose and Subsequent Risk of Anaphylaxis

Vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) represents our greatest hope to combat the devastating coronavirus disease 2019 (COVID-19) pandemic. Amid ongoing global vaccination efforts, rare cases of severe allergic reactions to COVID-19 mRNA vaccines have received significant attention. Although the exact nature of these reactions may be heterogeneous, various approaches exist to engage with patients, communities, public health departments, primary care providers, and other clinicians in a multidisciplinary approach to advance population health. Whereas it is optimal for patients to receive COVID-19 vaccination as outlined in emergency use authorizations, second-dose deferral of mRNA vaccines may be a consideration within a shared decision-making paradigm of care in select circumstances characterized by high durable first-vaccine–dose protection and significant elevations of vaccine anaphylaxis risk. Still, the durability of protection afforded by a single dose of a COVID-19 mRNA vaccine is uncertain, and alternative approaches to complete vaccination, including precautionary use of a COVID-19 viral vector vaccine, also remain patient-preference–sensitive options. There is an urgent need to define correlates of COVID-19 immunity and the level of longer-term protection afforded by COVID-19 vaccination.