Objective:
We develop an Excel-based tool to analyze model outputs for multiple parameter scenario combinations. The scenarios assess the impact of allowing cases into the community and dropping public health responses at different stages of the vaccine rollout. The scenarios allow for user-defined options for the infectiousness of the virus strain, the efficacy of the vaccine (against infection, symptoms, hospitalization, ICU and death), the maximum achievable coverage, and the vaccine rollout speed.
Findings:
- If cases begin to be introduced to the community before peak vaccine coverage has been achieved, there is a “race” between the time before a single case expands into an outbreak (noting that not all introduced cases result in an outbreak) and the time until vaccination coverage is sufficient to reach a herd immunity threshold.
- For the original variant, if cases started to be introduced when 60% vaccine coverage was reached, this would give the vaccine coverage a head start, and herd immunity could be reached before an outbreak takes off
- For the alpha variant, a vaccine with 50% efficacy at preventing infections would not be able to achieve herd immunity, even at 95% coverage. A vaccine with 75% protection against infection would require >80% coverage.
Implications:
These results suggest that with more infectious variant appearing, and with vaccine efficacy potentially waning over time, opening up borders before we reach peak vaccine coverage would likely lead to an uncontrolled epidemic wave. The result also suggest that an ongoing public health response to COVID-19 will be required, even with high vaccine coverage.
