Institute for International Programs, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, MD, USA.
Institute for International Programs, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, MD, USA.
Vaccine. 2019 Aug 23;37(36):5242-5249. doi: 10.1016/j.vaccine.2019.07.063. Epub 2019 Jul 30.
Delay in vaccination from schedule has been frequently documented and varies by vaccine, dose, and setting. Vaccination delay may result in the failure to prevent deaths that would have been averted by on-schedule vaccination. We constructed a model to assess the impact of delay in vaccination with pneumococcal conjugate vaccine (PCV) on under-five mortality. The model accounted for the week of age-specific risk of pneumococcal mortality, direct effect of vaccination, and herd protection. For each model run, a cohort of children were exposed to the risk of mortality and protective effect of PCV for each week of age from birth to age five. The model was run with and without vaccination delay and difference in number of deaths averted was calculated. We applied the model to eight country-specific vaccination scenarios, reflecting variations in observed vaccination delay, PCV coverage, herd effect, mortality risk, and vaccination schedule. As PCV is currently being scaled up in India, we additionally evaluated the impact of vaccination delay in India under various delay scenarios and coverage levels. We found deaths averted by PCV with and without delay to be comparable in all of the country scenarios when accounting for herd protection. In India, the greatest relative difference in deaths averted was observed at low coverage levels and greatest absolute difference was observed around 60% vaccination coverage. Under moderate delay scenarios, vaccination delay had modest impact on deaths averted by PCV in India across levels of coverage or vaccination schedule. Without accounting for herd protection, vaccination delay resulted in much greater failure to avert deaths. Our model suggests that realistic vaccination delay has a minimal impact on the number of deaths averted by PCV when accounting for herd effect. High population coverage can largely over-ride the deleterious effect of vaccination delay through herd protection.
疫苗接种的延迟在医学文献中经常被记录，并且因疫苗、剂量和接种环境而异。疫苗接种的延迟可能导致未能预防本可以通过按时接种疫苗来避免的死亡。我们构建了一个模型，以评估肺炎球菌结合疫苗（PCV）接种延迟对五岁以下儿童死亡率的影响。该模型考虑了特定周龄的肺炎球菌死亡率风险、疫苗接种的直接效果和群体保护作用。对于每个模型运行，一组儿童会在从出生到五岁的每个周龄期间暴露于死亡风险和 PCV 的保护作用之下。模型在有和没有接种延迟的情况下进行运行，并计算避免死亡的人数差异。我们将该模型应用于 8 个国家特定的疫苗接种场景，反映了观察到的接种延迟、PCV 覆盖率、群体效应、死亡率风险和疫苗接种时间表的差异。由于 PCV 目前正在印度扩大规模，我们还评估了在各种延迟场景和覆盖水平下印度接种延迟的影响。我们发现，在考虑群体保护的情况下，有和没有延迟接种的 PCV 可避免的死亡人数在所有国家场景中都是相当的。在印度，在低覆盖率水平下观察到的可避免死亡人数的相对差异最大，而在大约 60%的疫苗接种覆盖率下观察到的绝对差异最大。在中度延迟情况下，在印度，疫苗接种延迟对不同覆盖率或疫苗接种时间表下 PCV 可避免的死亡人数的影响不大。如果不考虑群体保护，疫苗接种延迟会导致 PCV 避免死亡的效果大大降低。我们的模型表明，考虑到群体效应，现实中的疫苗接种延迟对 PCV 可避免的死亡人数的影响很小。高人群覆盖率可以通过群体保护在很大程度上消除疫苗接种延迟的有害影响。
