An influenza circulation was observed in Myanmar between October and November in 2021. Patients with symptoms of influenza-like illness were screened using rapid diagnostic test (RDT) kits, and 147/414 (35.5%) upper respiratory tract specimens presented positive results. All RDT-positive samples were screened by a commercial multiplex real-time polymerase chain reaction (RT-PCR) assay, and 30 samples positive for influenza A(H3N2) or B underwent further typing/subtyping for cycle threshold (Ct) value determination based on cycling probe RT-PCR. The majority of subtyped samples (n = 13) were influenza A(H3N2), while only three were B/Victoria. Clinical samples with low Ct values obtained by RT-PCR were used for whole-genome sequencing via next-generation sequencing technology. All collected viruses were distinct from the Southern Hemisphere vaccine strains of the corresponding season but matched with vaccines of the following season. Influenza A(H3N2) strains from Myanmar belonged to clade 2a.3 and shared the highest genetic proximity with Bahraini strains. B/Victoria viruses belonged to clade V1A.3a.2 and were genetically similar to Bangladeshi strains. This study highlights the importance of performing influenza virus surveillance with genetic characterization of the influenza virus in Myanmar, to contribute to global influenza surveillance during the COVID-19 pandemic.

This study aimed to analyze the genetic and evolutionary characteristics of the influenza A/H3N2 viruses circulating in Myanmar from 2015 to 2019. Whole genomes from 79 virus isolates were amplified using real-time polymerase chain reaction and successfully sequenced using the Illumina iSeq100 platforms. Eight individual phylogenetic trees were retrieved for each segment along with those of the World Health Organization (WHO)-recommended Southern Hemisphere vaccine strains for the respective years. Based on the WHO clades classification, the A/H3N2 strains in Myanmar from 2015 to 2019 collectively belonged to clade 3c.2. These strains were further defined based on hemagglutinin substitutions as follows: clade 3C.2a (n = 39), 3C.2a1 (n = 2), and 3C.2a1b (n = 38). Genetic analysis revealed that the Myanmar strains differed from the Southern Hemisphere vaccine strains each year, indicating that the vaccine strains did not match the circulating strains. The highest rates of nucleotide substitution were estimated for hemagglutinin (3.37 × 10⁻³ substitutions/site/year) and neuraminidase (2.89 × 10⁻³ substitutions/site/year). The lowest rate was for non-structural protein segments (4.19 × 10⁻⁵ substitutions/site/year). The substantial genetic diversity that was revealed improved phylogenetic classification. This information will be particularly relevant for improving vaccine strain selection.

We estimated influenza vaccine effectiveness (VE) in 2015-2016 season against medically attended, laboratory-confirmed influenza, when quadrivalent inactivated vaccine (IIV4) was first introduced in Japan, using test-negative case-control design. Influenza A(H1N1)pdm09 cocirculated with B/Yamagata and B/Victoria during the study period in Japan. We based our case definition on two laboratory tests, real-time reverse transcription polymerase chain reaction (RT PCR), and virus isolation and compared VEs based on these tests. In addition, VE was evaluated by rapid diagnostic test (RDT). Nasopharyngeal swabs were collected from outpatients who visited clinics with influenza-like illness (ILIs) in Hokkaido, Niigata, Gunma and Nagasaki prefectures. Among 713 children and adults enrolled in this study, 578 were influenza positive by RT PCR including, 392 influenza A and 186 influenza B, while 135 were tested negative controls. The adjusted VE by RT PCR for all ages against any influenza was low protection of 36.0% (95% confidence interval [CI], 3.1% to 58.6%), for influenza A was 30.0% (95% CI: -10.0% to 55.5%), and influenza B was moderate 50.2% (95% CI: 13.3% to 71.4%). Adjusted VE for virus isolation for A(H1N1)pdm09 was 37.1% (95% CI: 1.7% to 59.7%), Yamagata lineage 51.3% (95% CI: 6.4% to 74.7%) and Victoria lineage 21.3% (95% CI: -50.0% to 58.9%). VE was highest and protective in 0-5 years old group against any influenza and influenza A and B/Yamagata, but the protective effect was not observed for other age groups and B/Victoria. RDT demonstrated concordant results with RT PCR and virus isolation. Sequencing of hemagglutinin gene showed that all A(H1N1)pdm09 belong to clade 6B including 31 strains (88.6%), which belong to clade 6B.1 possessing S162N mutations that may alter antigenicity and affect VE for A(H1N1)pdm09. IIV4 influenza vaccine during 2015-2016 was effective against A(H1N1)pdm09 and the two lineages of type B. Younger children was more protected than older children and adults by vaccination.

To evaluate the changes in respiratory syncytial virus (RSV) collected between 2019 and 2022, we analyzed RSV-A and RSV-B strains from various prefectures in Japan before and after the COVID-19 pandemic. RT-PCR-positive samples collected from children with rapid test positivity at outpatient clinics in 11 prefectures in Japan were sequenced for the ectodomain of the G gene to determine the genotype. Time-aware phylogeographic analyses were performed using the second hypervariable region (HVR) of the G gene from 2012 to 2022. Of 967 samples, 739 (76.4%) were found to be RSV-positive using RT-PCR. RSV peaked in September 2019 but was not detected in 2020, except in Okinawa. Nationwide epidemics occurred with peaks in July 2021 and 2022. The genotype remained the same, ON1 for RSV-A and BA9 for RSV-B during 2019–2022. Phylogeographic analysis of HVR revealed that at least seven clusters of RSV-A had circulated previously but decreased to two clusters after the pandemic, whereas RSV-B had a single monophyletic cluster over the 10 years. Both RSV-A and RSV-B were transferred from Okinawa into other prefectures after the pandemic. The RSV epidemic was suppressed due to pandemic restrictions; however, pre-pandemic genotypes spread nationwide after the pandemic.

We compared the duration of fever in children infected with A(H1N1)pdm09, A(H3N2), or influenza B viruses following treatment with baloxavir marboxil (baloxavir) or neuraminidase inhibitors (NAIs) (oseltamivir, zanamivir, or laninamivir). This observational study was conducted at 10 outpatient clinics across 9 prefectures in Japan during the 2012-2013 and 2019-2020 influenza seasons. Patients with influenza rapid antigen test positive were treated with one of four anti-influenza drugs. The type/subtype of influenza viruses were identified from MDCK or MDCK SIAT1 cell-grown samples using two-step real-time PCR. Daily self-reported body temperature after treatment were used to evaluate the duration of fever by treatment group and various underlying factors. Among 1742 patients <19 years old analyzed, 452 (26.0%) were A(H1N1)pdm09, 827 (48.0%) A (H3N2), and 463 (26.0%) influenza B virus infections. Among fours treatment groups, baloxavir showed a shorter median duration of fever compared to oseltamivir in univariate analysis for A(H1N1)pdm09 virus infections (baloxavir, 22.0 h versus oseltamivir, 26.7 h, P < 0.05; laninamivir, 25.5 h, and zanamivir, 25.0 h). However, this difference was not significant in multivariable analyses. For A(H3N2) virus infections, there were no statistically significant differences observed (20.3, 21.0, 22.0, and 19.0 h) uni- and multivariable analyses. For influenza B, baloxavir shortened the fever duration by approximately 15 h than NAIs (20.3, 35.0, 34.3, and 34.1 h), as supported by uni- and multivariable analyses. Baloxavir seems to have comparable clinical effectiveness with NAIs on influenza A but can be more effective for treating pediatric influenza B virus infections than NAIs.

We studied genetic variation in the second hypervariable region (HVR) of the G gene of human respiratory syncytial virus (HRSV) from 1701 nasal swab samples collected from outpatients with acute respiratory infections at two general hospitals in the cities Yangon and Pyinmana in Myanmar from 2015 to 2018. HRSV genotypes were characterized using phylogenetic trees constructed using the maximum likelihood method. Time-scale phylogenetic tree analyses were performed using the Bayesian Markov chain Monte Carlo method. In total, 244 (14.3%) samples were HRSV-positive and were classified as HRSV-A (n = 84, 34.4%), HRSV-B (n = 158, 64.8%), and co-detection of HRSV-A/HRSV-B (n = 2, 0.8%). HRSV epidemics occurred seasonally between July (1.9%, 15/785) and August (10.5%, 108/1028), with peak infections in September (35.8%, 149/416) and October (58.2%, 89/153). HRSV infection rate was higher in children ≥1 year of age than in those <1 year of age (70.5% vs. 29.5%). The most common HRSV symptoms in children were cough (80%-90%) and rhinorrhea (70%-100%). The predominant genotypes were ON1for HRSV-A (78%) and BA9 for HRSV-B (64%). Time to the most recent common ancestor was 2014 (95% highest posterior density [HPD], 2012-2015) for HRSV-A ON1 and 2009 (95% HPD, 2004-2012) for HRSV-B BA9. The mean evolutionary rate (substitutions/site/year) for HRSV-B (2.12 × 10^-2, 95% HPD, 8.53 × 10^-3-3.63 × 10^-2) was slightly higher than that for HRSV-A (1.39 × 10^-2, 95% HPD, 6.03 × 10^-3-2.12 × 10^-2). The estimated effective population size (diversity) for HRSV-A increased from 2015 to 2016 and declined in mid-2018, whereas HRSV-B diversity was constant in 2015 and 2016 and increased in mid-2017. In conclusion, the dominant HRSV-A and HRSV-B genotypes in Myanmar were ON1 and BA9, respectively, between 2015 and 2018. HRSV-B evolved slightly faster than HRSV-A and exhibited unique phylogenetic characteristics.