Seasonal influenza during the COVID-19 pandemic in Bangladesh

Abstract

Introduction During the 2019 novel coronavirus infectious disease (COVID-19) pandemic in 2020, limited data from several countries suggested reduced seasonal influenza viruses’ circulation. This was due to community mitigation measures implemented to control the pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We used sentinel surveillance data to identify changes in the 2020 influenza season compared with previous seasons in Bangladesh. Methods We used hospital-based influenza surveillance (HBIS) data of Bangladesh that are generated year-round and are population-representative severe acute respiratory infection (SARI) data for all age groups from seven public and two private tertiary care level hospitals data from 2016 to 2019. We applied the moving epidemic method (MEM) by using R language (v4.0.3), and MEM web applications (v2.14) on influenza-positive rates of SARI cases collected weekly to estimate an average seasonal influenza curve and establish epidemic thresholds. Results The 2016–2019 average season started on epi week 18 (95% CI: 15–25) and lasted 12.5 weeks (95% CI: 12–14 weeks) until week 30.5. The 2020 influenza season started on epi week 36 and ended at epi week 41, lasting for only five weeks. Therefore, influenza epidemic started 18 weeks later, was 7.5 weeks shorter, and was less intense than the average epidemic of the four previous years. The 2020 influenza season started on the same week when COVID-19 control measures were halted, and 13 weeks after the measures were relaxed. Conclusion Our findings suggest that seasonal influenza circulation in Bangladesh was delayed and less intense in 2020 than in previous years. Community mitigation measures may have contributed to this reduction of seasonal influenza transmission. These findings contribute to a limited but growing body of evidence that influenza seasons were altered globally in 2020.

SARS-CoV-2 and influenza virus coinfection among patients with severe acute respiratory infection during the first wave of COVID-19 pandemic in Bangladesh: a hospital-based descriptive study

“…Influenza season during 2019–2020 ended very early in China compared with previous years, 7 and there was a sharp decline of influenza circulation in the USA and several Asian countries 8–11 of the Northern Hemisphere, including in Bangladesh. 6 Similar observations were also reported in the Southern Hemisphere countries of Australia, Chile, South Africa and New Zealand. 12 13 This decline in influenza virus activity might be attributed to many factors, including the substantial outbreak of SARS-CoV-2 as a global pandemic and public health efforts to control this virus.…”

“…During the 12.5 weeks (May–July) of peak influenza circulation time in Bangladesh, 6 we did not detect any circulating influenza till 14 weeks from the start of the peak influenza season. Several public health control efforts in Bangladesh were undertaken from the mid-March epi (week-13) to control the COVID-19 pandemic.…”

“… 33 34 Since both SARS-CoV-2 and influenza viruses have similar modes of transmission through respiratory and contact routes, 14 these public health pandemic control efforts may have completely limited the transmission of influenza virus circulation in Bangladesh during its peak season. 6 Similar marked influenza circulation reductions were also reported in Singapore, Thailand, China, Taiwan and New Zealand during the COVID-19 pandemic citing as a collateral effect of pandemic control measures as the predominant cause. 8–11 13 …”

“…1–4 Bangladesh is a tropical country in the northern hemisphere, but the annual seasonal influenza epidemic occurs typically during the monsoon period, that is, from May to September, 5 with influenza peak activity for 12.5 weeks on average spanning from May (epi-weeks 18) and July (epi-weeks 30.5) every year. 6 …”

“… 12 13 This decline in influenza virus activity might be attributed to many factors, including the substantial outbreak of SARS-CoV-2 as a global pandemic and public health efforts to control this virus. 6 8 12 13 Both influenza and SARS-CoV-2 produce similar clinical manifestations like—fever, cough, headache, muscle and joint pain, severe malaise, sore throat, runny nose, anosmia and ageusia. 14 Furthermore, SARS-CoV-2 and influenza viruses share the common route of human‐to‐human transmission through aerosolised or respiratory droplets.…”