Determining Safe NPI Relaxation Strategy in India During the Delta and Omicron Waves of COVID-19: Findings from a Two-Strain COVID-19 Transmission model Open Access
Wu, Ting-Hsuan (Spring 2022)
Published
Abstract
The use of non-pharmaceutical interventions (NPIs) has been a critical strategy to slow and prevent the spread of SARS-CoV-2 during the COVID-19 pandemic. Dynamic transmission models have been developed to project the course of the pandemic under various assumptions. This study aimed to validate model-projected COVID-19 cases and deaths for the Delta wave to assess model performance and project the course of the pandemic during the time period where transmission is driven by the Omicron variant. We updated the parameters of a two-strain SEIR model and compared model-projected and reported COVID-19 cases and deaths in India over 180 days starting from July 27th, 2021. The difference (projected – reported) and percent error were calculated to assess the degree of agreement between model projections and the reported data. Following external validation, we updated model parameters with the best estimates corresponding to the Omicron wave and projected the number of COVID-19 cases and deaths over 180 days beginning from November 26th, 2021. When NPI relaxation is delayed for at least 180 days, model-projected cases for the Delta wave aligned with reported number of cases in India. Between days 30 and 75, the Onam holiday was celebrated, and model projections underestimated the number of reported cases during this time. If the Onam spike is excluded, model-projected cases closely aligned with reported data, with a mean error of 1.7% and -2.0% for the 12-week and 24-week (full SDE) inter-dose intervals, respectively. The model projected 518 deaths per million after 150 days, which overestimated the 352 deaths per million reported in India. Projections for the Omicron wave suggest that cases will peak earlier than they did in the Delta wave, with a smaller second peak occurring later during the simulation period. External validation of the two-strain SEIR model suggests that the model was consistent with cases in India and that NPIs continued to reduce transmission throughout the six-month period, but validation work must continue as more data on the characteristics of the Omicron variant become available.
Table of Contents
Table of Contents
Introduction 1
Variants of Concern, Non-pharmaceutical Interventions (NPIs), and Vaccines 1
Models 5
Model Verification and Validation 6
Objective/Aim 7
Method 8
SEIR Model Structure 8
Model Parameters 9
Parameter Validation 10
External Validation 11
Omicron Simulation 12
Results 12
Parameter Validation 12
External Validation for the Delta Wave 13
Omicron Projections 14
Discussion 15
External Validation 16
Omicron Simulation 17
Limitation 18
Implications and Future Directions 18
Tables and Figures 20
Figure 1 20
Table 1 21
Table 2 23
Figure 2 24
Figure 3 25
Figure 4 26
Table 3 27
Figure 5 28
Figure 6 29
Figure 7 30
Figure 8 31
References 32
Supplementary Materials 41
S1 41
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