Estimating long-term vaccine effectiveness against SARS-CoV-2 variants: a model-based approach

Evaluation of the effectiveness of COVID-19 vaccines is increasingly challenging due to high levels of exposure to infection and vaccination. Here, the authors use a model-based approach incorporating these factors and estimate that using a variant-matched rather than ancestral booster could prevent nearly twice as many hospitalisations and deaths over one year. With the ongoing evolution of the SARS-CoV-2 virus updated vaccines may be needed. We fitted a model linking immunity levels and protection to vaccine effectiveness data from England for three vaccines (Oxford/AstraZeneca AZD1222, Pfizer-BioNTech BNT162b2, Moderna mRNA-1273) and two variants (Delta, Omicron). Our model reproduces the observed sustained protection against hospitalisation and death from the Omicron variant over the first six months following dose 3 with the ancestral vaccines but projects a gradual waning to moderate protection after 1 year. Switching the fourth dose to a variant-matched vaccine against Omicron BA.1/2 is projected to prevent nearly twice as many hospitalisations and deaths over a 1-year period compared to administering the ancestral vaccine. This result is sensitive to the degree to which immunogenicity data can be used to predict vaccine effectiveness and uncertainty regarding the impact that infection-induced immunity (not captured here) may play in modifying future vaccine effectiveness.

Automated summary

This study uses a model-based approach to estimate that using a variant-matched booster vaccine could prevent nearly twice as many hospitalizations and deaths as using an ancestral booster. Updated vaccines may be needed due to the ongoing evolution of the virus.