PP20 -Post pandemic period circulation and seasonality of SARS-CoV-2 : Analysis of samples from National Respiratory Reference Laboratory, Jan 2023- Dec 2024
Abstract
Introduction
SARS-CoV-2, the causative agent of the COVID-19 pandemic, continues to circulate globally following the lifting of the status of Public Health Emergency of International Concern (PHEIC) by the World Health Organization on 5th May 2023. The National Influenza Centre (NIC), serving as the national reference laboratory for respiratory viruses, has maintained extensive testing for SARS-CoV-2, providing a comprehensive picture of seasonality and trends for public health measures.
Objectives
To determine the observed prevalence of SARS-CoV-2, seasonality/trend, and compare them with influenza seasonality from the samples received from January 2023 to December 2024.
Design, setting, and methods
A retrospective analysis was conducted on 7,831 respiratory specimens received between January 2023 and December 2024 from OPD, inpatient, and sentinel surveillance sites nationwide. Testing was performed using the CDC Influenza SARS-CoV-2 multiplex and Altona SARS-CoV-2 PCR assays. Monthly positivity trends were analyzed using the Chi-square test and compared with 2022 data. SARS-CoV-2 and influenza were tested simultaneously on the same samples following WHO surveillance protocols.
Results
A total of 7,831 samples were analyzed, comprising 2,469 in 2023 (with a monthly average of 205) and 5,362 in 2024 (with a monthly average of 447). There were two clear SARS-CoV-2 peaks during the post-pandemic period: a primary peak from April to June, with the highest positivity in May (8% in 2023; 17.6% in 2024), and a secondary peak from November to early January, highest in December (5.6% in 2023; 5.8% in 2024). These findings were statistically significant (p < 0.05). For comparison, 2022 data, analyzed separately, showed major pandemic-phase peaks: 41% in January and 35% in August, with a smaller rise in December (10%). Influenza displayed consistent bimodal seasonality from March to June and November to February across 2023–2024.
Conclusion
From 2023 to 2024, SARS-CoV-2 demonstrated low prevalence with two seasonal peaks: April to June and November to January. These periods overlap with the established bimodal seasonality of influenza. These findings are crucial for tailoring public health interventions and preparedness strategies.
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