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Impact of vaccination by priority group on UK deaths, hospital admissions and intensive care admissions from COVID‐19

Our take —

Authors sought to model the impact of the UK’s vaccination program and targeting of priority groups on COVID-19 associated hospitalizations, ICU admissions, and deaths. Authors adjusted models by age group, priority group, and clinical risk and vulnerability. Methods are poorly described, making it difficult to follow the motivation for different assumptions. Overall, these assumptions ignore the dynamical processes that drive disease transmission and outcomes, thus limiting utility and replicability of the analysis.

Study design

Modeling/Simulation

Study population and setting

Authors sought to estimate the effect of the UK’s vaccination plan on the number of COVID-19-associated hospitalizations, ICU admissions, and deaths among ten priority groups. Authors estimated these impacts using data from the UK’s vaccine delivery plan, population size estimates for each priority group, and deaths, hospitalizations, and ICU admissions per priority group and for the total UK population. Authors assumed every individual in priority groups 1 through 4 will have received their first dose by mid-February 2021, uptake within priority groups will be 100%, that the current distribution of clinical outcomes would mirror those in summer 2020, and vaccination is 100% effective in preventing these outcomes (but does not reduce transmission). Various models adjusted for age groups, extremely clinically vulnerable groups, and/or health worker- and social worker-specific admissions. Authors used the above described empirical data to reallocate the age distribution based on these priority groups. Overall, methods were poorly documented and may not be replicable.

Summary of Main Findings

Authors reported the cumulative impact of vaccination by age group first. If adults >80 years were vaccinated, 62% of deaths, 33% of hospital admissions, and 3% of ICU admissions were prevented; if all adults 18 and older were vaccinated, deaths, hospitalizations, and ICU admissions were all reduced by 100%. Authors then adjusted for priority group. When groups 1 and 2 (care home residents and workers, healthcare workers, social care workers, and adults aged 80+) were vaccinated, 63% of deaths, 37% of hospitalizations, and 8% of ICU admissions were prevented; when all groups (1 through 10) were vaccinated, all measures were reduced by 100%. Finally, when authors reallocated health and social workers (i.e., those extremely clinically vulnerable and at risk) into different priority groups, vaccinating groups 1 and 2 reduced deaths by 63%, hospitalizations by 37%, and ICU admissions by 8%; 100% of these measures were prevented when all 10 groups were vaccinated.

Study Strengths

Authors conducted sensitivity analyses to estimate the impact of vaccines assuming only 90% uptake and/or 90% vaccine effectiveness. Percent reduction of the clinical outcomes was smaller when less-than-perfect uptake and effectiveness was assumed, however, these reductions were relatively minor.

Limitations

Overall, methods were difficult to understand and insufficiently detailed. Data on COVID-19 associated hospital admissions by age group were from February to April 2020; ICU admissions and deaths by age group were from June 2020. At the time of publication, these data were up to one year old and may be considerably outdated. The assumption that infection during the second wave will mirror dynamics seen during the first wave is not likely to be realistic in real-world settings, especially in the context of ongoing mitigation efforts – including vaccination – and the emergence of new viral strains. The modeling does not consider the immunity profile in the population given the history of natural infections that have occurred over the past year. Even at baseline, care and the age burden of infection has changed over time and it seems unlikely that the distribution of outcomes in that first wave would remain the same now. This method also does not seem to consider changes in infection, hospitalization, ICU admission and/or death rates over time (or in changes to relative rates between priority groups over time) as vaccines are rolled out. It is not clear what the “end” time point is for evaluating vaccine impacts. Finally, authors only report cumulative effects of vaccination by age group or priority group, limiting the interpretability of these estimates for specific groups.

Value added

This modeling study attempts to provide potential guidance for monitoring the effectiveness of the UK’s COVID-19 vaccination program and the impact targeting priority groups has on severe clinical outcomes. However, unfounded assumptions about immunity and the age-specific risk of infection and severe outcomes and poorly documented methods limit any potential value added from this study.

This review was posted on: 19 April 2021