Whole-Genome Analysis of Influenza A(H3N2) and B/Victoria Viruses Detected in Myanmar during the COVID-19 Pandemic in 2021

Influenza Virus: Genomic Insights, Evolution, and its Clinical Presentation

Influenza viruses belong to the family Orthomyxoviridae and have been a concern for public health due to frequent epidemics and sporadic waves of pandemics. According to WHO, seasonal strains of the influenza A virus (IAV) infect 3 to 5 million people every year and result in 0.29 to 0.65 million deaths globally. Among all proteins of IAV, the haemagglutinin (HA) and neuraminidase (NA) have high mutation rates and have been reported to undergo antigenic drift and shift leading to novel strains. Hence continuous revision in drugs and vaccines regime is an economic burden as these reassortments can cause high morbidity among the immunologically naive population. Infection rates are higher among older age groups, infants and patients reported with other respiratory distress. Routine diagnostic tests include reverse transcription polymerase chain reaction (RT-PCR), viral culture, and immunofluorescence assays; however, the diagnosis may be hindered due to the resemblance of the clinical presentation of other respiratory viruses with influenza viruses. Here we present a comprehensive review which sheds light on the genomic structure, evolution, pathogenicity and clinical presentation of influenza virus that can help to distinguish it from other respiratory viruses. A detailed analysis will ultimately pave the way for the development of more effective antiviral drugs and a universal vaccine.

Molecular epidemiological surveillance of respiratory syncytial virus infection in Myanmar from 2019 to 2023

To evaluate genetic changes in respiratory syncytial virus (RSV) between 2019 and 2023, we analyzed RSV strains from Myanmar before and after the COVID- 19 pandemic. Real-time polymerase chain reaction (RT-PCR) positive samples from children presenting with acute respiratory infections at outpatient clinics in Yangon were sequenced to determine the genotype. Phylogenetic and molecular evolutionary analyses were conducted using the Bayesian Markov Chain Monte Carlo method to construct the time-scale Maximum Clade Credibility tree. Of 1127 samples, 104 (9.2%) RSV-A and 233 (20.7%) RSV-B were positive by RT-PCR. There was an absence of a notable epidemic in 2020, a temporal shift with a surge of RSV-A in the 2021 outbreak, a lack of expected cases in 2022 and a substantial resurgence of RSV-B in 2023. The genotype of RSV-A was mainly A.D.3 lineage through the study period, while RSV-B were B.D.4.1.1 and B.D.E.1. RSV-A showed that the same lineage persisted within Myanmar throughout the pandemic, leading to a large outbreak post-COVID. In contrast, RSV-B strains appear to have temporarily disappeared during the pandemic, but subsequently, globally circulating strains likely entered Myanmar, resulting in a major outbreak in 2023. The estimated evolutionary rate at the G-ectodomain for RSV-A was 7.76 × 10⁻³ and RSV-B was 5.67 × 10⁻³ substitutions/site/year. Strengthening genomic surveillance will likely support comparisons of circulating strains with those in other countries and facilitate the introduction of vaccines and other interventions.

Neuraminidase-specific antibodies drive differential cross-protection between contemporary FLUBV lineages

The two influenza B virus (FLUBV) lineages have continuously diverged from each other since the 1980s, with recent (post-2015) viruses exhibiting accelerated evolutionary rates. Emerging data from human studies and epidemiological models suggest that increased divergence in contemporary viruses may drive differential cross-protection, where infection with Yamagata lineage viruses provides limited immunity against Victoria lineage viruses. Here, we developed animal models to investigate the mechanisms behind asymmetric cross-protection between contemporary FLUBV lineages. Our results show that contemporary Victoria immunity provides robust cross-protection against the Yamagata lineage, whereas Yamagata immunity offers limited protection against the Victoria lineage. This differential cross-protection is driven by Victoria-elicited neuraminidase (NA)-specific antibodies, which show cross-lineage reactivity, unlike those from Yamagata infections. These findings identify a phenomenon in contemporary FLUBV that may help explain the recent disappearance of the Yamagata lineage from circulation, highlighting the crucial role of targeting NA in vaccination strategies to enhance cross-lineage FLUBV protection.

Detection of influenza A(H3N2) viruses with polymerase acidic subunit substitutions after and prior to baloxavir marboxil treatment during the 2022-2023 influenza season in Japan

Baloxavir marboxil (baloxavir), approved as an anti-influenza drug in Japan in March 2018, can induce reduced therapeutic effectiveness due to PA protein substitutions. We assessed PA substitutions in clinical samples from influenza-infected children and adults pre- and post-baloxavir treatment, examining their impact on fever and symptom duration. During the 2022-2023 influenza season, the predominant circulating influenza subtype detected by cycling-probe RT-PCR was A(H3N2) (n = 234), with a minor circulation of A(H1N1)pdm09 (n = 10). Of the 234 influenza A(H3N2) viruses collected prior to baloxavir treatment, 2 (0.8%) viruses carry PA/I38T substitution. One virus was collected from a toddler and one from an adult, indicating the presence of viruses with reduced susceptibility to baloxavir, without prior exposure to the drug. Of the 54 paired influenza A(H3N2) viruses collected following baloxavir treatment, 8 (14.8%) viruses carried E23 K/G, or I38 M/T substitutions in PA. Variant calling through next-generation sequencing (NGS) showed varying proportions (6-100 %), a polymorphism and a mixture of PA/E23 K/G, and I38 M/T substitutions in the clinical samples. These eight viruses were obtained from children aged 7-14 years, with a median fever duration of 16.7 h and a median symptom duration of 93.7 h, which were similar to those of the wild type. However, the delayed viral clearance associated with the emergence of PA substitutions was observed. No substitutions conferring resistance to neuraminidase inhibitors were detected in 37 paired samples collected before and following oseltamivir treatment. These findings underscore the need for ongoing antiviral surveillance, informing public health strategies and clinical antiviral recommendations for seasonal influenza.

Whole-Genome Analysis of the Influenza A(H1N1)pdm09 Viruses Isolated from Influenza-like Illness Outpatients in Myanmar and Community-Acquired Oseltamivir-Resistant Strains Present from 2015 to 2019

In this study, we describe the genetic characteristics of influenza A(H1N1)pdm09 strains detected in Myanmar from 2015 to 2019. Whole genomes from 60 A(H1N1)pdm09 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. A(H1N1)pdm09 viruses from 2015 were found to belong to clade 6B, those from 2016 to 6B.1, 2017 to 6B.1A, and 2019 to 6B.1A.5a, and were genetically distinct from the Southern Hemisphere vaccine strains for the respective seasons, A/California/7/2009 and A/Michigan/45/2015. We observed one virus with intra-subtype reassortment, collected in the 2015 season. Importantly, three viruses possessed the H275Y substitution in the neuraminidase protein, appearing to be community-acquired without the prior administration of neuraminidase inhibitors. These viruses exhibited highly reduced susceptibility to oseltamivir and peramivir. This study demonstrates the importance of monitoring genetic variations in influenza viruses that will contribute to the selection of global influenza vaccines.

Probable extinction of influenza B/Yamagata and its public health implications: a systematic literature review and assessment of global surveillance databases

Early after the start of the COVID-19 pandemic, the detection of influenza B/Yamagata cases decreased globally. Given the potential public health implications of this decline, in this Review, we systematically analysed data on influenza B/Yamagata virus circulation (for 2020-23) from multiple complementary sources of information. We identified relevant articles published in PubMed and Embase, and data from the FluNet, Global Initiative on Sharing All Influenza Data, and GenBank databases, webpages of respiratory virus surveillance systems from countries worldwide, and the Global Influenza Hospital Surveillance Network. A progressive decline of influenza B/Yamagata detections was reported across all sources, in absolute terms (total number of cases), as positivity rate, and as a proportion of influenza B detections. Sporadically reported influenza B/Yamagata cases since March, 2020 were mostly vaccine-derived, attributed to data entry errors, or have yet to be definitively confirmed. The likelihood of extinction necessitates a rapid response in terms of reassessing the composition of influenza vaccines, enhanced surveillance for B/Yamagata, and a possible change in the biosafety level when handling B/Yamagata viruses in laboratories.

Genomic Analyses Uncover Evolutionary Features of Influenza A/H3N2 Viruses in Yunnan Province, China, from 2017 to 2022

Influenza A viruses evolve at a high rate of nucleotide substitution, thereby requiring continuous monitoring to determine the efficacy of vaccines and antiviral drugs. In the current study, we performed whole-genome sequencing analyses of 253 influenza A/H3N2 strains from Yunnan Province, China, during 2017-2022. The hemagglutinin (HA) segments of Yunnan A/H3N2 strains isolated during 2017-2018 harbored a high genetic diversity due to heterogeneous distribution across branches. The mutation regularity of the predominant antigenic epitopes of HA segments in Yunnan was inconsistent in different years. Some important functional mutations in gene segments associated with viral adaptation and drug tolerance were revealed. The rapid genomic evolution of Yunnan A/H3N2 strains from 2017 to 2022 mainly concentrated on segments, i.e., matrix protein 2 (M2), non-structural protein 1 (NS1), neuraminidase (NA), NS2, and HA, with a high overall non-synonymous/synonymous substitution ratio (dN/dS). Our results highlighted a decline in vaccine efficacy against the A/H3N2 circulating strains, particularly against the Yunnan 2021-2022 A/H3N2 strains. These findings aid our understanding of evolutionary characteristics and epidemiological monitoring of the A/H3N2 viruses and provide in-depth insights into the protective efficacy of influenza vaccines.