Abstract
Background
The COVID-19 pandemic posed major challenges to health systems across the globe over the past two years. For a lower-middle income class country such as the Philippines with limited resources, its health system is more susceptible to being overwhelmed whenever there is a surge of COVID-19 infections and hospitalizations. Because of this, the monitoring and management of health capacity is a key component in the Philippine government’s pandemic response.
Methods
To contribute to this initiative, the FASSSTER team developed compartmental models and provided corresponding outputs that would give a picture of the potential burden that the Philippine health system may face over the course of this pandemic. The aforementioned models are represented as a set of differential equations, which describe the dynamics of disease transmission. Scenario-based outputs produced by the FASSSTER models were regularly used as evidence for national, regional and city-wide policies.
Results
The first model was a modified SEIR model, which placed members of the population into six compartments: Susceptible (S), Exposed (E), Infectious and Asymptomatic (Ia), Infectious and Symptomatic (Is), Confirmed (C) and Recovered (R). Projection outputs from the C compartment, which comprise the Active Cases, were used to derive estimates of moderate, severe and critical cases; to be specific, 19% of active cases were assumed to be moderate or severe, while 1% of active cases were assumed to be critical. The numbers generated for these COVID-19 outcomes were then utilized to compute health system requirements, which include the number of hospital beds, health care workers, and other health care needs.
The threat of the Delta variant and the wide-scale deployment of vaccinations by mid-year of 2021 necessitated the development of an updated FASSSTER model. The second model builds on the previous one by adding vaccinated compartments, partial and fully vaccinated, to account for their increased protection against infection. Estimates of severe and critical case numbers that can help inform health capacity planning were then derived from the active case projections of the model, the local data provided by the Department of Health Data Collect (DDC), and effectiveness of vaccines to prevent hospitalization among those who were infected.
A third iteration of the compartmental model was developed at the beginning of the year 2022 in response to the emergence of the Omicron variant. The updated model includes a boosted compartment, composed of individuals who have received an additional dose after completing their primary doses. The model also allowed for reinfections to occur, due to the immune evasive nature of the Omicron variant in relation to the previous strains circulating in the country. After generating active case projections from this model, estimates for severe and critical case numbers were also produced based on the historical trend of these outcomes over the past year. In this paper, we highlight selected scenarios where health systems capacity estimates were used as evidence for informing policy decisions. At present, the FASSSTER model continues to be used to monitor health systems capacity as one determinant in mitigating the spread of COVID-19.