During the 2019 novel coronavirus disease (COVID-19) pandemic in 2020, limited data from several countries suggested reduced circulation of seasonal influenza viruses. We applied the moving epidemic method (MEM) to influenza surveillance data from 2016 to 2019 in Bangladesh to estimate an average seasonal influenza curve and establish epidemic thresholds. The 2020 influenza epidemic started 18 weeks later, was 7.5 weeks shorter, and was less intense than the average curve of the four previous years. These findings contribute to a limited but growing body of evidence that influenza seasons were altered globally in 2020.

Background We explored whether hospital-based surveillance is useful in detecting severe acute respiratory infection (SARI) clusters and how often these events result in outbreak investigation and community mitigation. Methods During May 2009– December 2020, physicians at 14 sentinel hospitals prospectively identified SARI clusters (i.e., ≥2 SARI cases who developed symptoms ≤10 days of each other and lived <30 minute walk or <3 km from each other). Oropharyngeal and nasopharyngeal swabs were tested for influenza and other respiratory viruses by rRT-PCR. We describe the demographic of persons within clusters, laboratory results, and outbreak investigations. Results Physicians identified 464 clusters comprising 1,427 SARI cases (range 0–13 clusters per month). Sixty percent of clusters had three, 23% had 2, and 17% had ≥4 cases. Their median age was 2 years (interquartile [IQR] 0.4–25) and 63% were male. Laboratory results were available for the 464 clusters a median 9 days (IQR = 6–13 days) after cluster identification. Less than one in five clusters had cases that tested positive for the same virus: RSV in 58 (13%), influenza viruses in 24 (5%), HMPV in 5 (1%), HPIV in 3 (0.6%), adenovirus in 2 (0.4%). While 102/464 (22%) had poultry exposure, none tested positive for influenza A(H5N1) or A(H7N9). None of the 464 clusters led to field deployments for outbreak response. Conclusions For 11 years, none of the hundreds of identified clusters led to emergency response. The value of this event-based surveillance might be improved by seeking larger clusters, with stronger epidemiologic ties or decedents.

It is impossible to address the many complex needs of respiratory virus surveillance with a single system. Therefore, multiple surveillance systems and complementary studies must fit together as tiles in a “mosaic” to provide a complete picture of the risk, transmission, severity, and impact of respiratory viruses of epidemic and pandemic potential. Below we present a framework to assist national authorities to identify priority respiratory virus surveillance objectives and the best approaches to meet them; to develop implementation plans according to national context and resources; and to prioritize and target technical assistance and financial investments to meet most pressing needs.

In March 2021, Lao People’s Democratic Republic (Laos) reported an avian influenza A(H5N6) virus infection in a 5-year-old child identified through sentinel surveillance. This was the first human A(H5N6) infection reported outside of China. A multidisciplinary investigation undertook contact tracing and enhanced human and animal surveillance in surrounding villages and live bird markets. Seven Muscovy ducks tested positive for highly pathogenic avian influenza A(H5N6) viruses. Sequenced viruses belonged to clade 2.3.4.4h and were closely related to viruses detected in poultry in Vietnam, and to previous viruses detected in Laos. Surveillance and coordinated outbreak response remain essential to global health security.

Background: Adults with cardiopulmonary conditions are at increased risk for complications from influenza and respiratory syncytial virus (RSV) infection, but few data are available from middle-income countries. Methods: Using data from a prospective cohort study of influenza vaccine effectiveness among community-dwelling Thai adults aged ≥65 years, we estimated and compared the incidence of influenza and RSV in those with and without cardiopulmonary conditions. During May 2015-May 2017, older adults in a rural province in Thailand were followed weekly with year-round surveillance for acute respiratory illness (ARI), defined broadly as new onset or worsening of cough with or without fever, and hospitalized ARI. When ill, nasal self-swabs and/or nasopharyngeal swabs were collected for reverse-transcription polymerase chain reaction testing. We used Poisson regression to calculate incidence rate ratios (IRR), adjusting for age, sex, past healthcare-seeking behavior, weekly influenza activity, and influenza vaccination. Results: Overall, 3,220 adults with a median age of 71 years (IQR 68-76) were enrolled; 1,324 (41.1%) were male; and 313 (9.7%) had ≥1 underlying cardio-pulmonary condition, most commonly chronic obstructive pulmonary disease (131; 41.2%) or asthma (73; 23.3%). Compared to those without, participants with cardiopulmonary conditions had higher incidences of ARI, influenza, and RSV (Adjusted IRR: 1.83, 95% CI 1.63-2.05; 1.84, 95% CI 1.05-3.23; 2.02, 95% CI 1.10-3.72, respectively). Conclusion: Our findings show that older adults in rural Thailand with cardiopulmonary conditions have increased rates of ARI, influenza, and RSV infections, and support efforts to ensure this population has access to influenza vaccines and other respiratory illness prevention measures.

Global influenza virus circulation declined and has been below traditional seasonal levels during the COVID-19 pandemic.1-3 We reviewed WHO influenza surveillance outputs from May 1-December 31, 2020 (epidemiologic weeks 18-53) from tropical Asian countries. For each country we report influenza surveillance specimens tested, and the percentage positive for influenza, by type and subtype. We compared current data to historical data from 2015-2019 in order to place the current season in historical context. Twelve included countries tested 17,407 surveillance specimens, with 592 (3.4%) testing positive for influenza viruses. From April 27-July 26, 2020 (epidemiologic weeks 18-30), specimens tested decreased from an average of 14,102 per year in 2015-2019 to 3,969 (71.9% decrease) and influenza positivity from 22% to <1%. During weeks 31-53, specimens tested decreased from an average of 24,782 per year in 2015-2019 to 13,438 (45.8% decrease) and influenza positivity from 18% to 4%. In six countries that maintained testing of surveillance specimens for >90% of weeks, influenza circulation was unseasonably low, or absent, during weeks 18-30, 2020. However, during weeks 31-53, the percentage of surveillance specimens testing positive for influenza approached or reached positivity rates of 2015-2019 in Bangladesh and Cambodia; and increased but remained lower than historical positivity in Lao PDR and Viet Nam. The data presented here are a reminder that the low levels of influenza circulation in the northern hemisphere in summer 2020 may not necessarily persist into the upcoming influenza season, and influenza surveillance and prevention strategies should continue as planned and not be delayed.