Deviation from the recommended schedule: optimal dosing interval for a two-dose vaccination programme.

Area of Science:

• Epidemiology
• Mathematical Modeling
• Public Health Policy

Background:

• Limited vaccine supply during emerging infectious diseases necessitates strategic deployment.
• Balancing broad population coverage with optimal individual protection is a key challenge.
• The COVID-19 pandemic highlighted policy dilemmas regarding vaccine dosing intervals.

Purpose of the Study:

• To compare the public health impact of single-dose COVID-19 vaccination strategies versus the standard two-dose schedule.
• To evaluate the influence of first-dose efficacy on the effectiveness of delayed second-dose strategies.
• To identify conditions under which delaying the second vaccine dose is optimal for reducing infections, hospitalizations, and deaths.

Main Methods:

• Development and application of a delay-differential equation model.
• Inclusion of parameters for waning immunity and vaccine distribution capacity.
• Comparative analysis of vaccination strategies based on simulated epidemiological outcomes.

Main Results:

• First-dose efficacy is a critical factor determining the success of delayed second-dose vaccination.
• Delayed vaccination can reduce short-term hospitalizations and deaths, even with suboptimal first-dose efficacy, despite potential increases in infections.
• Optimal delay duration varies based on the specific health outcome (infection, hospitalization, death) and evaluation timeframe.

Conclusions:

• Vaccination policy decisions must consider the trade-offs between infection rates and severe outcomes.
• The effectiveness of delaying the second vaccine dose is context-dependent and not universally superior to the standard schedule.
• Results challenge previous assumptions and highlight the need for nuanced, data-driven vaccination strategies in public health emergencies.