The Return of Wintertime Respiratory Virus Outbreaks and Shifts in the Age Structure of Incidence in the Southern Hemisphere

Clinical, Genomic, and Immunological Characterization of RSV Surge in Sydney, Australia, 2022

OBJECTIVES

The 2022 seasonal respiratory syncytial virus (RSV) epidemic in Sydney, Australia saw an unprecedented number of RSV detections. We aimed to characterize genomic and immunologic factors associated with the surge in RSV cases.

METHODS

Whole genome sequences of RSV were generated from 264 RSV-infected infants and linked to case-matched clinical data from the 2022 southern hemisphere RSV season. We then performed an immunologic analysis of baseline RSV-specific humoral immunity in women of childbearing age before and throughout the coronavirus disease 2019 pandemic.

RESULTS

Clinical analysis revealed a high burden of disease across patients of all health backgrounds. More than one-half of RSV-related health care visits by infants resulted in hospitalization, and one-quarter required high-flow respiratory support or a higher level of care. Viral phylogenetic analyses revealed that 2022 Sydney RSV sequences were closely related to viruses that had been circulating globally since 2017, including those detected in recent US outbreaks. Nonsynonymous mutations within the palivizumab and nirsevimab binding sites were detected at low frequencies. There was no difference in baseline RSV-neutralizing antibody titers between 2020 and 2022.

CONCLUSIONS

Collectively, these findings suggest that neither the emergence of a novel RSV genotype nor hypothesized immune debt was associated with the surge of RSV cases and hospitalizations in 2022. Continued genomic and immunologic surveillance is required to further understand the factors driving outbreaks of RSV globally, and to inform guidelines for the rollout and ongoing use of recently developed immunotherapeutics and vaccines.

The impact of current and future climates on spatiotemporal dynamics of influenza in a tropical setting

Although the drivers of influenza have been well studied in high-income settings in temperate regions, many open questions remain about the burden, seasonality, and drivers of influenza dynamics in the tropics. In temperate climates, the inverse relationship between specific humidity and transmission can explain much of the observed temporal and spatial patterns of influenza outbreaks. Yet, this relationship fails to explain seasonality, or lack there-of, in tropical and subtropical countries. Here, we analyzed eight years of influenza surveillance data from 12 locations in Bangladesh to quantify the role of climate in driving disease dynamics in a tropical setting with a distinct rainy season. We find strong evidence for a nonlinear bimodal relationship between specific humidity and influenza transmission in Bangladesh, with highest transmission occurring for relatively low and high specific humidity values. We simulated influenza burden under current and future climate in Bangladesh using a mathematical model with a bimodal relationship between humidity and transmission, and decreased transmission at very high temperatures, while accounting for changes in population immunity. The climate-driven mechanistic model can accurately capture both the temporal and spatial variation in influenza activity observed across Bangladesh, highlighting the usefulness of mechanistic models for low-income countries with inadequate surveillance. By using climate model projections, we also highlight the potential impact of climate change on influenza dynamics in the tropics and the public health consequences.

Impact of public health measures and new introducing variants on Respiratory syncytial virus recrudescence in Taiwan during the COVID-19 pandemic

OBJECTIVES

Respiratory syncytial virus (RSV) causes clinically significant distress in children and adults. Non-pharmaceutical interventions against SARS-CoV-2 have affected the seasonal activity of common respiratory pathogens. This seems exceptionally true regarding RSV's seasonal circulation, hence we have investigated the changes in the epidemiology of RSV in Taiwan during the pandemic.

MATERIALS

A prospective surveillance of RSV among hospitalized children was carried out between 2020 and 2022 in central Taiwan. Of all PCR-detected RSV, genotype and evolutionary analysis were further investigated. Demographics and clinical features were compared between each outbreak.

RESULTS

Throughout the consecutive three years of the SARS-CoV-2 pandemic, RSV outbreaks took place in Taiwan first in 2020 and a second time in 2022. We enrolled 80 and 105 hospitalized child cases, in each surge respectively. The RSV G protein genomic analysis revealed that RSV ON1 and RSV BA9 were separately contributing to these two outbreaks, and evolutionary evidence indicated these RSV variants are new to Taiwan, with their own featured sets of mutations. Clinically, a shift in age of RSV infected children was found, but the clinical severity was not worse and remained independent of RSV genotype.

CONCLUSIONS

There were two delayed RSV surges after the relaxation of public measures during the pandemic in Taiwan, and both outbreaks were driven by new RSV genetic variants rather than cryptic circulation of the previous genetic clusters in Taiwan. These findings highlight the importance of continued surveillance on the trend and evolution of RSV after the COVID-19 pandemic.