Temporal Shifting of Influenza Subtype Dynamics in Pakistan Following the COVID‐19 Pandemic: A 10‐Year FluNet Analysis, 2015–2024

BACKGROUND: The COVID-19 pandemic and associated nonpharmaceutical interventions caused unprecedented suppression of influenza circulation globally. Pakistan, with its high population density and evolving surveillance capacity, lacks long-term data on post-COVID-19 influenza patterns, essential for guiding vaccine policy. METHODS: We extracted weekly virological data for Pakistan from the WHO FluNet platform (January 1, 2015, to December 31, 2024). The study period was divided into pre-COVID-19 (2015-2019), COVID-19 disruption (2020-2021), and post-COVID-19 (2022-2024) phases. Outcomes included type A versus B proportion, subtype distribution (A[H1N1]pdm09 vs. A[H3]), positivity, peak intensity, and season duration (weeks with positivity ≥ 10%). Statistical comparisons used chi-square for subtype distribution and Kruskal-Wallis for peak intensity. RESULTS: We analyzed 6522 positive specimens from 79,484 tested (10,781 pre-COVID-19; 14,687 during COVID-19 disruption; 54,016 post-COVID-19). Influenza A declined from 94.2% to 71.7% then rose to 77.5%; influenza B increased from 5.7% to 28.3%, remaining at 22.5% (p < 0.001). A(H3) dominated during the COVID-19 disruption (98.8%); A(H1N1)pdm09 regained dominance post-COVID-19 (58.8%), though A(H3) remained higher than pre-COVID-19 (41.2% vs. 33.3%). Peak intensity differed (p = 0.047): pre-COVID-19 33.3%-67.6%; COVID-19 disruption 14.0%-17.6%; and post-COVID-19 19.8%-37.8%. Season duration was 1 week in 2020 and 3 non-consecutive weeks in 2021, versus 10-16 weeks pre-COVID-19, recovering to 7-13 weeks post-COVID-19. CONCLUSION: The COVID-19 pandemic induced a lasting shift in Pakistan's influenza epidemiology, with persistently elevated influenza B and reshaped A subtype balance. These findings are consistent with the global disappearance of B/Yamagata and support consideration of trivalent vaccine formulations, though antigenic and genetic data remain necessary to confirm vaccine match.