Vaccination strategies for minimizing loss of life in Covid-19 in a Europe lacking vaccines

Aim and BackgroundWe aimed at identifying vaccination strategies that minimize loss of life in the Covid-19 pandemic. Covid-19 mainly kills the elderly, but the pandemic is driven by social contacts that are more frequent in the young. Vaccines elicit stronger immune responses per dose in younger persons. As vaccine production is a bottleneck, many countries have adopted a strategy of first vaccinating the elderly and vulnerable, while postponing vaccination of the young. MethodsBased on published age-stratified immunogenicity data of the Moderna mRNA-1273 vaccine, we compared the established "one dose fits all" approach with tailored strategies: The known differential immunogenicity of vaccine doses in different age groups is exploited to vaccinate the elderly at full dose, while the young receive a reduced dose, amplifying the number of individuals receiving the vaccine early. A modeling approach at European Union scale with population structure, Covid-19 case and death rates similar to Europe in late January 2021 is used. ResultsWhen the elderly were vaccinated preferentially, the pandemic initially continued essentially unchecked, as it was dominantly driven by social contacts in other age groups. Tailored strategies, including regular dosing in the elderly but reduced dose vaccination in the young, multiplied early vaccination counts, and even with some loss in protection degree for the individual person, the protective effect towards stopping the pandemic and protecting lives was enhanced, even for the elderly. In the European Union, pandemic duration (threshold >100000 cases/day) was shortened from 53 to 18-24 days; cumulative death count over 100 days was reduced by >30000. Data suggest that the findings may be relevant to both, the Moderna and the Pfizer-BioNTech mRNA vaccines. ConclusionProtecting the vulnerable, minimizing overall deaths and stopping the pandemic is best achieved by an adaptive vaccination strategy using an age-tailored vaccine dose, in this model parameterized to European demographics, coronavirus transmission observations and vaccine characteristics.