Impact of vaccine supplies and delays on optimal control of the COVID-19 pandemic:mapping interventions for the Philippines

Background::Around the world,controlling the COVID-19 pandemic requires national coordination of multiple intervention strategies.As vaccinations are globally introduced into the repertoire of available interventions,it is important to consider how changes in the local supply of vaccines,including delays in administration,may be addressed through existing policy levers.This study aims to identify the optimal level of interventions for COVID-19 from 2021 to 2022 in the Philippines,which as a developing country is particularly vulnerable to shifting assumptions around vaccine availability.Furthermore,we explore optimal strategies in scenarios featuring delays in vaccine administration,expansions of vaccine supply,and limited combinations of interventions.Methods::Embedding our work within the local policy landscape,we apply optimal control theory to the compartmental model of COVID-19 used by the Philippine government’s pandemic surveillance platform and introduce four controls:(a)precautionary measures like community quarantines,(b)detection of asymptomatic cases,(c)detection of symptomatic cases,and(d)vaccinations.The model is fitted to local data using an L-BFGS minimization procedure.Optimality conditions are identified using Pontryagin’s minimum principle and numerically solved using the forward-backward sweep method.Results::Simulation results indicate that early and effective implementation of both precautionary measures and symptomatic case detection is vital for averting the most infections at an efficient cost,resulting in>99%reduction of infections compared to the no-control scenario.Expanding vaccine administration capacity to 440,000 full immunizations daily will reduce the overall cost of optimal strategy by 25%,while allowing for a faster relaxation of more resource-intensive interventions.Furthermore,delays in vaccine administration require compensatory increases in the remaining policy levers to maintain a minimal number of infections.For example,delaying the vaccines by 180 days(6 months)will result in an 18%increase in the cost of the optimal strategy.Conclusion::We conclude with practical insights regarding policy priorities particularly attuned to the Philippine context,but also applicable more broadly in similar resource-constrained settings.We emphasize three key takeaways of(a)sustaining efficient case detection,isolation,and treatment strategies;(b)expanding not only vaccine supply but also the capacity to administer them,and;(c)timeliness and consistency in adopting policy measures.

The effect of mixed vaccination rollout strategy:A modelling study

Vaccines have measurable efficacy obtained first from vaccine trials.However,vaccine efficacy(VE)is not a static measure and long-term population studies are needed to evaluate its performance and impact.COVID-19 vaccines have been developed in record time and the currently licensed vaccines are extremely effective against severe disease with higher VE after the full immunization schedule.To assess the impact of the initial phase of the COVID-19 vaccination rollout programmes,we used an extended Susceptible-Hospitalized-Asymptomatic/mild-Recovered(SHAR)model.Vaccination models were proposed to evaluate different vaccine types:vaccine type 1 which protects against severe disease only but fails to block disease transmission,and vaccine type 2 which protects against both severe disease and infection.VE was assumed as reported by the vaccine trials incorporating the difference in efficacy between one and two doses of vaccine administration.We described the performance of the vaccine in reducing hospitalizations during a momentary scenario in the Basque Country,Spain.With a population in a mixed vaccination setting,our results have shown that reductions in hospitalized COVID-19 cases were observed five months after the vaccination rollout started,from May to June 2021.Specifically in June,a good agreement between modelling simulation and empirical data was well pronounced.