Impact of vaccination delay on deaths averted by pneumococcal conjugate vaccine: Modeled effects in 8 country scenarios

Abstract

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.

Impact of COVID-19 pandemic response on uptake of routine immunizations in Sindh, Pakistan: An analysis of provincial electronic immunization registry data

“…Our study shows a delay in the vaccination of children because of the lockdown. Previous studies have shown, without accounting for herd protection, that delays in vaccination can cause up to 6% more deaths from vaccine-preventable diseases such as Pneumonia in Pakistan [53] . We note that the value of vaccines and essential immunization in preventing deaths and children’s suffering largely override the risks of COVID-19 infection.…”

Early estimates of the indirect effects of the COVID-19 pandemic on maternal and child mortality in low-income and middle-income countries: a modelling study

“…Second, in countries with higher vaccination coverage, 80% of the unvaccinated cohort would remain protected by the herd effect. 28 Because of the scarcity of evidence on the herd protection offered by meningococcal A vaccine and diphtheria-tetanus-pertussis vaccine, and the high coverage threshold for herd protection for measles vaccine, we did not attenuate the effects of these vaccines; rather, we assumed the full effect of the coverage reduction on mortality.…”

Determinants of vaccine coverage and timeliness in a northern Pakistani village

“…The local schedule, despite being out of synchrony with the national one, was rigorously maintained, suggestive of a robust vaccination system even though an assessment may conclude that vaccines were given increasingly late. It is unlikely that this modest shift in schedule adversely affects the protection afforded from vaccination and modelling of pneumococcal vaccines suggests that the interval between doses has little impact on effectiveness [ 29 ]. A likely explanation for the difference between the local and national schedules is the fact that free vaccines were only available on a once-a-week basis by a visiting EPI vaccinator.…”