Optimal Timing of Vaccination: A Narrative Review of Integrating Strategies for COVID-19, Influenza, and Respiratory Syncytial Virus

Lower respiratory tract infections caused by SARS-CoV-2, influenza, and respiratory syncytial virus (RSV) cause a significant disease burden globally, despite the availability of effective vaccines. Certain populations, such as older adults (≥ 60 years) and individuals of all ages with particular comorbidities, are at increased risk for severe outcomes, including hospitalization and death. National administration schedules for available vaccines against respiratory viruses are not unified, and not all current guidelines are clear and directive, concerning the optimal timing of vaccination. Herein, we formulate an evidence-based position regarding the optimal timing of COVID-19, influenza, and RSV vaccination for older adults and individuals with chronic comorbidities, based on a synthesis of the literature and current guidelines. Vaccination impact and timing were found to be influenced by vaccinee risk factors, including age and comorbidities, and waning vaccine effectiveness and seasonal pathogen burden. Because COVID-19, influenza, and RSV display unique seasonal patterns within and between regions, local epidemiological surveillance of each virus is crucial for determining optimal vaccination timing and guidelines. To maximize the benefits of these respiratory virus vaccines, the timing of peak vaccine effectiveness and period of greatest risk for severe outcomes should be aligned. Thus, COVID-19, influenza, and other recommended vaccines given ahead of the start of the respiratory virus season (or other regionally appropriate time) and co-administered at a single, routine visit represent the optimal approach to protecting at-risk populations. More data will be required to establish the clinical benefit of additional RSV vaccine doses and whether these may be integrated within a seasonal schedule. Coordinated policy decisions that align with strain selection for new and annually reformulated vaccines would enable the timely raising of public health awareness, ultimately leading to enhanced vaccine uptake. Implementation strategies will require engagement of healthcare providers and strong, evidence-based public health recommendations for integrated vaccine schedules.