Exploring immunity debt: Dynamic alterations in RSV antibody levels in children under 5 years during the COVID-19 pandemic

Immunity Debt for Seasonal Influenza After the COVID-19 Pandemic and as a Result of Nonpharmaceutical Interventions: An Ecological Analysis and Cohort Study

Non-pharmaceutical interventions (NPIs) during the COVID-19 pandemic significantly reduced influenza transmission. This study explores the hypothesis of "immunity debt" which suggests increased vulnerability to influenza following reduced exposure during the pandemic. World Health Organization aggregated data on influenza from 116 countries and its association with NPI intensity as measured by the COVID-19 Stringency Index is analyzed. Where individual-level data available (France, the United Kingdom, Spain, Italy, Belgium, and Romania), the analyses of influenza monthly rates in six European countries (France, the United Kingdom, Spain, Italy, Belgium, and Romania) are replicated. The results indicate globally a 46.3% (95% CI: 15.79-70.78%) reduction in influenza cases during COVID-19 restrictions in the winter season, followed by a 131.7% (95% CI: 34.95-255.78%) increase in the first postrelaxation winter and a 161.2% (95% CI: 31.88-382.16%) increase in the summer as compared to the predicted level based on historical influenza epidemic trends. In addition, a positive association between the Stringency Index and post-relaxation influenza surge is observed globally (R2 = 0.14-0.17) and replicated regionally. The findings support the population immunity debt hypothesis for influenza and call for proactive preparations against its consequences in future pandemics.

Distinct seasonality and increased respiratory failure in RSV patients < 2 years of age after emergence of SARS-CoV-2: data from the multicentric, prospective PAPI study

Respiratory syncytial virus (RSV) is a leading cause for global infant morbidity and mortality. The COVID-19 pandemic caused significant shifts in seasonality of RSV, and changes in disease severity have been matter of intense discussion. Between September 2020 and February 2023, the multicentric, prospective PAPI study analyzed rates and phenotypes of hospitalized RSV patients aged ≤ 24 months across three German hospitals. Pseudonymized patient data were analyzed employing Mann-Whitney U and chi-square testing, or one-way ANOVA or Kruskal-Wallis testing when more than two groups were compared. Additionally, RSV cases from seasons 2017/2018-2020/2021 were retrospectively analyzed. After its absence in 2020/2021, RSV returned approximately 2 months earlier than usual in late 2021. Overall duration of the season and patient numbers were comparable to previous seasons, and no significant shifts in age and gender distributions occurred in our cohort. While duration of hospitalization did not differ between the periods before vs. after the emergence of SARS-CoV-2, a significantly higher rate of patients with hypoxemia and respiratory failure occurred after the onset of the pandemic (oxygen supplementation post vs. pre: 59.4% vs. 54.8%, p < 0.001, non-invasive ventilation post vs. pre: 12.4% vs. 7.2%; p < 0.001). No deaths occurred during the entire observational period.

CONCLUSION

We present comprehensive data on distinct seasonality and increased disease severity in children hospitalized with RSV bronchiolitis before and after the onset of the SARS-CoV-2 pandemic. Our data aids in understanding the impact of the pandemic on RSV disease in infants and provides valuable information on the impact of RSV on pediatric healthcare prior to broad introduction of novel prevention measures such as nirsevimab.

WHAT IS KNOWN

• Respiratory syncytial virus (RSV) is a leading cause of infant morbidity and mortality globally. • COVID-19 has led to significant shifts in RSV seasonality, and concerns about shifts in RSV severity.

WHAT IS NEW

• This study shows distinct seasonality and significant shifts in diseases severity amongst children with RSV associated hospitalization under the age of 2 yrs in the last years in Germany. • It reports significantly higher rates of RSV associated respiratory failures in children < 2 yrs. of age after emergence of the pandemic.

Rebound of Antibiotic Use and Respiratory Infections After Resumption of Normalcy From COVID-19 in Hong Kong

Purpose

During COVID-19 pandemic, use of antimicrobial has been shown to be reduced coupled with various respiratory infections. We investigated whether this effect on reduction of antibiotic prescription can be sustained after resumption of normalcy and lifting of public health measures.

Methods

We compared the wholesale supply of antimicrobials using mean annual Daily Defined Dose/1000 inhabitants (DID) in different sectors in pre-COVID-19 (2014-2019), COVID-19 (2020-2022) and post-COVID-19 (2023) periods. We grouped the data according to AWaRe categorisation namely Access, Watch and Reserve defined by WHO, and analysed the trends of the top 10 antibiotics and broad-spectrum antimicrobials. The trends in statutory notifiable diseases including scarlet fever, pneumococcal infections, chickenpox, tuberculosis, and pertussis and influenza-like-illness detected by sentinel surveillance system was analysed by negative-binominal regression.

Results

Compared to baseline level, an overall reduction of 27.2% of antimicrobial utilization was observed during the pandemic years, with a rebound recorded in 2023, up to 89.5% of the pre-pandemic level. The access group of antimicrobials accounted for 57.9% in 2014 gradually increased to 60.2% in 2023 across the pandemic years. Concurrently, reduction in incidence of scarlet fever, pneumococcal infections, chickenpox, tuberculosis, pertussis and influenza-like-illness was observed during COVID-19 pandemic with statistical decreasing trend, p<0.05 for scarlet fever, pneumococcal infections and chickenpox. Rebound in all these infections was reported in 2023, except for chickenpox which showed continued decrease in incidence.

Conclusion

We demonstrated a substantial reduction of antibiotic use during the COVID-19 pandemic, which rebounded in 2023, likely due to increased incidence of respiratory diseases after lifting of public health and social measures. We urged for close monitoring of the antimicrobial resistance pattern of different bacteria due to the inter-connectiveness and global impact of these two pandemics.

Shifts in Respiratory Virus Epidemiology on Reunion Island From 2017 to 2023: Impact of COVID-19 Pandemic and Non-Pharmaceutical Interventions

Background

The COVID‐19 pandemic has reshaped the landscape of respiratory viral infections globally. This study examines these changes on Reunion Island, a French department in the southeastern Indian Ocean.

Methods

Retrospective data from 2017 to 2023, from over 24,000 samples collected across the hospital system, partner laboratories, and a network of sentinel physicians, were analyzed and correlated with the number of consultations at the hospital emergency department and with sentinel physicians for symptoms of acute respiratory infections (ARIs). The epidemiology of respiratory viruses was analyzed by comparing the pre‐ and post‐COVID‐19 periods to assess disruptions in seasonal patterns, changes in virus prevalence, and the affected age groups.

Results

Our database effectively captured the epidemiology of respiratory infections across the island, as demonstrated by its strong correlation with the number of consultations for ARI. Post‐COVID‐19, the influenza virus exhibited multiple epidemic waves within a single year, deviating from its traditional single annual peak and showing a significant decline in circulation from 2020 to 2023. The circulation of respiratory syncytial virus was also impacted post‐COVID‐19, with epidemics starting earlier and lasting longer compared with pre‐COVID‐19 years. Human rhinovirus circulated more prominently in the post‐COVID period, accounting for up to one‐third of positive cases, becoming the most prevalent respiratory virus (excluding SARS‐CoV‐2).

Conclusions

These findings suggest a notable impact of the COVID‐19 pandemic and associated NPIs on respiratory virus circulation on Reunion Island since mid‐2020. They underscore the complex interplay between viral interference, public health interventions, behavioral changes, and youth immunity, emphasizing the need for adaptable strategies in managing respiratory virus outbreaks in the post‐COVID‐19 era.

Changes in Respiratory Viruses' Activity in Children During the COVID-19 Pandemic: A Systematic Review

Background/Objectives: The impact of the coronavirus disease 2019 (COVID-19) pandemic on health was significant worldwide. The measures adopted to limit the spread of the virus had an indirect effect on the epidemiology of other infectious diseases with similar mechanisms of inter-human transmission. The present literature review analyzed the scenario of pediatric acute respiratory infections in the post-lockdown period compared to the pre-pandemic and lockdown periods. The different patterns of viruses' outbreaks were evaluated according to the type of local COVID-19 restrictive measures and to the type of pathogen. Methods: Relevant scientific literature published between March 2020 and November 2024 was identified by means of electronic keyword searches in the PubMed, Scopus, and Cochrane Library databases. Results: Worldwide implementation of non-pharmacological public health interventions aimed at limiting the COVID-19 pandemic resulted in a measurable effect on the circulation of other common respiratory viruses, significantly affecting their usual seasonality. Most viruses significantly reduced their activity during the lockdown period but returned to or exceeded historical levels after discontinuation of preventive non-pharmacological measures. For many respiratory viruses, particularly respiratory syncytial virus, an off-season increase was reported. Conclusions: The non-pharmacological interventions, which effectively helped limit the COVID-19 pandemic, resulted in relevant epidemiologic changes in most common respiratory viruses. Given the different seasonality and clinical severity observed for some pathogens after lockdown, possible future off-season or more severe epidemics should be expected.

Decline of Antibodies to Major Viral and Bacterial Respiratory Pathogens During the COVID-19 Pandemic

Surges in infections caused by respiratory pathogens have been documented in multiple settings after relaxation of pandemic restrictions. Antibodies to major antigens from respiratory syncytial virus and group A Streptococcus waned significantly in a longitudinal adult cohort throughout the pandemic. This waning may have contributed to the pathogen-surges that followed.

Impact of COVID-19 pandemic measures on hospitalizations and epidemiological patterns of twelve respiratory pathogens in children with acute respiratory infections in southern China

OBJECTIVES

To investigate the impact of COVID-19 pandemic measures on hospitalizations and the alterations and persistence of the epidemiological patterns of 12 common respiratory pathogens in children during the COVID-19 pandemic and after the cessation of the "zero-COVID-19" policy in southern China.

METHODS

Respiratory specimens were collected from hospitalized children with acute respiratory infections at Shenzhen Children's Hospital from January 2020 to June 2024. Twelve common respiratory pathogens were detected using multiplex PCR. Data on demographic characteristics, pathogen detection rates, epidemiological patterns, co-infections, and ICU admission rates were compared between the 'during COVID-19' period (Phase 1: January 2020 to December 2022) and the 'post COVID-19' period (Phase 2: January 2023 to June 2024).

RESULTS

In Phase 2, there was a significant increase in average annual cases, with a higher median age of affected children, higher pathogen detection rates, and increased co-infection rates compared to Phase 1. The epidemiological patterns of most pathogens were altered by the COVID-19 pandemic. Human Parainfluenza Virus, Human Metapneumovirus, Human Bocavirus (HBOV), and Human Coronavirus remained active during Phase 1, while Mycoplasma pneumoniae (Mp) and Adenovirus (ADV) were low, and Respiratory Syncytial Virus (RSV) lacked a seasonal peak in 2022. In Phase 2, Mp, ADV, and RSV experienced outbreaks, with Mp's high prevalence continuing into 2024. RSV showed out-of-season epidemics for two consecutive years. Influenza A (H1N1), Influenza A (H3N2), and InfB lost their seasonal patterns during Phase 1 but reemerged and regained their seasonal characteristics in 2023-2024. ICU admission rates did not significantly differ between the two phases, except for HBOV, which had higher rates in Phase 2.

CONCLUSION

The epidemiological patterns of various respiratory pathogens were affected by the COVID-19 pandemic to varying degrees. Pathogens suppressed during the pandemic experienced outbreaks or out-of-season epidemics after the lifting of non-pharmaceutical interventions, with Mp and RSV continuing into the second year and HBOV associated ICU admission rates increasing in the post-pandemic era. Continuous monitoring of these patterns is essential to understand the duration of these effects and to inform effective response strategies.

Analysis of respiratory pathogen detection in hospitalized children with acute respiratory tract infections after ending the zero COVID policy

After ending the three-year zero COVID policy in China, the epidemiology of other respiratory pathogens has been affected. This study aimed to characterize of common respiratory pathogen infections in pediatric patients hospitalized for acute respiratory tract infections (ARTIs) in Suzhou before and after ending the zero COVID policy. Nasopharyngeal aspirates (NPAs) were obtained from children with ARTIs (aged ≤ 16 years) at the Children's Hospital of Soochow University for the detection of respiratory syncytial virus (RSV), influenza A (FluA), FluB, human parainfluenza virus (HPIV), adenovirus (ADV), human rhinovirus (HRV), bocavirus (BoV), human metapneumovirus (HMPV), and mycoplasma pneumoniae (MP). The data were compared between two periods: January 2020 to December 2022 (before ending the zero COVID policy) and January 2023 to May 2024 (after ending the zero COVID policy). Patients were divided into four groups: 0-2, ≥ 3-5, ≥ 6-10, and ≥ 11-16 years. A total of 42,379 patients were enrolled and the top four pathogens identified were MP, HRV, RSV and HPIV with positive rates of 20.2%, 19.5%, 15.1%, and 6.9%, respectively. A total of 28,352 positive cases were detected, with positive rates of 54.0% (n = 11,850/21,941) and 80.7% (n = 16,502/20,438) before and after ending the zero COVID policy, respectively. Total RSV, HRV, HPIV, and MP positivity increased by 27.8%, 39.0%, 12.3%, and 322.7%, respectively, after ending the zero COVID policy compared to positivity before the policy. After ending the zero COVID policy, the positive rates of RSV, HRV, and HPIV increased most in children aged 0-2 years, with increases by 88.8% (OR: 2.3, 95% CI: 2.2-2.5), 50.0% (OR: 1.6, 95% CI: 1.5-1.7), and 69.6% (OR: 1.8, 95% CI: 1.6-2.0), respectively. The greatest increase in MP positivity was 316.9% in the 3-5 years (OR: 5.5, 95% CI: 4.9-6.1). After ending the zero COVID policy, the RSV-positive rate increased most in summer, while HRV was predominantly circulated in spring and the MP-positive rate peaked in autumn. Ending the zero COVID policy facilitated the transmission of common respiratory pathogens in children. Post-pandemic surveillance and control of respiratory pathogens must be strengthened to reduce health risks.

The pattern of childhood infections during and after the COVID-19 pandemic

The rates of most paediatric infectious diseases declined during the initial phase of the COVID-19 pandemic due to the implementation of non-pharmaceutical interventions. However, after the gradual release of these interventions, resurgences of infections occurred with notable variations in incidence, clinical manifestations, pathogen strains, and age distribution. This Review seeks to explore these changes and the rare clinical manifestations that were made evident during the resurgence of known childhood infections. The magnitude of resurgences was possibly caused by a profound population immunity debt to specific pathogens in combination with the coinciding reappearance of viral and bacterial infections, rather than novel pathogen variants, increased antimicrobial resistance, or altered childhood immune function. As the usual patterns of paediatric infectious diseases were disrupted during the COVID-19 pandemic, the consequences of a population immunity debt were unravelled, and new insights into pathogen transmissibility, disease pathogenesis, and rare clinical manifestations were revealed.

Comparison of characteristics of children hospitalized for respiratory syncytial virus infection during the pre- and post-COVID-19 eras: a multicenter retrospective study

BACKGROUND

Respiratory syncytial virus (RSV), a leading cause of lower respiratory tract infection (LRTI) among children, has resurged in the form of endemic or even pandemic in many countries and areas after the easing of COVID-19 containment measures. This study aimed to investigate the differences in epidemiological and clinical characteristics of children hospitalized for RSV infection during pre- and post-COVID-19 eras in Yunnan, China.

METHODS

A total of 2553 pediatric RSV inpatients from eight hospitals in Yunnan were retrospectively enrolled in this study, including 1451 patients admitted in 2018-2019 (pre-COVID-19 group) and 1102 patients admitted in 2023 (post-COVID-19 group). According to the presence or absence of severe LRTI (SLRTI), patients in the pre- and post-COVID-19 groups were further divided into the respective severe or non-severe subgroups, thus analyzing the risk factors for RSV-associated SLRTI in the two eras. Demographic, epidemiological, clinical, and laboratory data of the patients were collected for the final analysis.

RESULTS

A shift in the seasonal pattern of RSV activity was observed between the pre-and post-COVID-19 groups. The peak period of RSV hospitalizations in the pre-COVID-19 group was during January-April and October-December in both 2018 and 2019, whereas that in the post-COVID-19 group was from April to September in 2023. Older age, more frequent clinical manifestations (fever, acute otitis media, seizures), and elevated laboratory indicators [neutrophil-to-lymphocyte ratio (NLR), c-reactive protein (CRP), interleukin 6 (IL-6), co-infection rate] were identified in the post-COVID-19 group than those in the pre-COVID-19 group (all P < 0.05). Furthermore, compared to the pre-COVID-19 group, the post-COVID-19 group displayed higher rates of SLRTI and mechanical ventilation, with a longer length of hospital stay (all P < 0.05). Age, low birthweight, preterm birth, personal history of atopy, underlying condition, NLR, IL-6 were the shared independent risk factors for RSV-related SLRTI in both pre- and post-COVID-19 groups, whereas seizures and co-infection were independently associated with SLRTI only in the post-COVID-19 group.

CONCLUSIONS

An off-season RSV endemic was observed in Yunnan during the post-COVID-19 era, with changed clinical features and increased severity. Age, low birthweight, preterm birth, personal history of atopy, underlying condition, NLR, IL-6, seizures, and co-infection were the risk factors for RSV-related SLRTI in the post-COVID-19 era.

Immunity Debt Regarding the Aspect of Influenza in the Post-COVID-19 Era in Taiwan

Immunity debt for various viral infections was reported globally in the post-COVID-19 era, but the data about influenza are lacking. This study collected data from Taiwan's CDC Open Data Portal. We analyzed the weekly number of influenza hospitalizations from January 2017 to May 2024. We divided the study period into four phases: the pre-COVID-19 without influenza epidemics, pre-COVID-19 with an influenza epidemic, COVID-19 pandemic lockdown control, and COVID-19 pandemic unlock periods. The Wilcoxon rank-sum test and interrupted time series analysis were used. The median case numbers of the four time periods were 174 (IQR = 98), 431 (IQR = 160), 8, and 155 (IQR = 175), respectively. Under the COVID-19 pandemic lockdown control, the weekly influenza hospitalization case number decreased by 90.2% (p < 0.001). The non-pharmaceutical intervention (NPI) policies during the COVID-19 pandemic helped Taiwan reduce influenza hospitalizations significantly. Till now, a comparison of the prevalence of influenza pre-COVID-19 and post-COVID-19 has yet to be reported. In our study, with the pandemic unlocking, it increased by 20-fold (p < 0.001), but the case number was still significantly lower than that pre-COVID-19. Amongst other factors, this may be associated with continuing self-induced NPIs in Taiwan.

Development and validation of a nomogram for predicting occurrence of severe case in children hospitalized with influenza A (H1N1) infection during the post-COVID-19 era

Background

The significant rebound of influenza A (H1N1) virus activity, particularly among children, with rapidly growing number of hospitalized cases is of major concern in the post-COVID-19 era. The present study was performed to establish a prediction model of severe case in pediatric patients hospitalized with H1N1 infection during the post-COVID-19 era.

Methods

This is a multicenter retrospective study across nine public tertiary hospitals in Yunnan, China, recruiting pediatric H1N1 inpatients hospitalized at five of these centers between February 1 and July 1, 2023, into the development dataset. Screening of 40 variables including demographic information, clinical features, and laboratory parameters were performed utilizing Least Absolute Shrinkage and Selection Operator (LASSO) regression and logistic regression to determine independent risk factors of severe H1N1 infection, thus constructing a prediction nomogram. Receiver operating characteristic (ROC) curve, calibration curve, as well as decision curve analysis (DCA) were employed to evaluate the model's performance. Data from four independent cohorts comprised of pediatric H1N1 inpatients from another four hospitals between July 25 and October 31, 2023, were utilized to externally validate this nomogram.

Results

The development dataset included 527 subjects, 122 (23.1 %) of whom developed severe H1N1 infection. The external validation dataset included 352 subjects, 72 (20.5 %) of whom were eventually confirmed as severe H1N1 infection. The LASSO regression identified 19 candidate predictors, with logistic regression further narrowing down to 11 independent risk factors, including underlying conditions, prematurity, fever duration, wheezing, poor appetite, leukocyte count, neutrophil-lymphocyte ratio (NLR), erythrocyte sedimentation rate (ESR), lactate dehydrogenase (LDH), interleukin-10 (IL-10), and tumor necrosis factor-α (TNF-α). By integrating these 11 factors, a predictive nomogram was established. In terms of prediction of severe H1N1 infection, excellent discriminative capacity, favorable accuracy, and satisfactory clinical usefulness of this model were internally and externally validated via ROC curve, calibration curve, and DCA, respectively.

Conclusion

Our study successfully established and validated a novel nomogram model integrating underlying conditions, prematurity, fever duration, wheezing, poor appetite, leukocyte count, NLR, ESR, LDH, IL-10, and TNF-α. This nomogram can effectively predict the occurrence of serious case in pediatric H1N1 inpatients during the post-COVID-19 era, facilitating the early recognition and more efficient clinical management of such patients.

A novel combined nomogram for predicting severe acute lower respiratory tract infection in children hospitalized for RSV infection during the post-COVID-19 period

Introduction

Off-season upsurge of respiratory syncytial virus (RSV) infection with changed characteristics and heightened clinical severity during the post-COVID-19 era are raising serious concerns. This study aimed to develop and validate a nomogram for predicting the risk of severe acute lower respiratory tract infection (SALRTI) in children hospitalized for RSV infection during the post-COVID-19 era using machine learning techniques.

Methods

A multicenter retrospective study was performed in nine tertiary hospitals in Yunnan, China, enrolling children hospitalized for RSV infection at seven of the nine participating hospitals during January-December 2023 into the development dataset. Thirty-nine variables covering demographic, clinical, and laboratory characteristics were collected. Primary screening and dimension reduction of data were performed using Least Absolute Shrinkage and Selection Operator (LASSO) regression, followed by identification of independent risk factors for RSV-associated SALRTI using Logistic regression, thus finally establishing a predictive nomogram model. Performance of the nomogram was internally evaluated by receiver operating characteristic (ROC) curve, calibration curve, and decision curve analysis (DCA) based on the development dataset. External validation of our model was conducted using same methods based on two independent RSV cohorts comprising pediatric RSV inpatients from another two participating hospitals between January-March 2024.

Results

The development dataset included 1102 patients, 239 (21.7%) of whom developed SALRTI; while the external validation dataset included 249 patients (142 in Lincang subset and 107 in Dali subset), 58 (23.3%) of whom were diagnosed as SALRTI. Nine variables, including age, preterm birth, underlying condition, seizures, neutrophil-lymphocyte ratio (NLR), interleukin-6 (IL-6), lactate dehydrogenase (LDH), D-dimer, and co-infection, were eventually confirmed as the independent risk factors of RSV-associated SALRTI. A predictive nomogram was established via integrating these nine predictors. In both internal and external validations, ROC curves indicated that the nomogram had satisfactory discrimination ability, calibration curves demonstrated good agreement between the nomogram-predicted and observed probabilities of outcome, and DCA showed that the nomogram possessed favorable clinical application potential.

Conclusion

A novel nomogram combining several common clinical and inflammatory indicators was successfully developed to predict RSV-associated SALRTI. Good performance and clinical effectiveness of this model were confirmed by internal and external validations.

Alterations of pathogen transmission patterns and attenuated immune stimulation might be the cause of increased adult respiratory infections cases in 2023, results from a multi-center study in mainland China

Background

Several respiratory infections outbreaks have been observed in mainland China after reduction of non-pharmaceutical interventions. Other countries have seen increases in respiratory infections outside typical seasons post-COVID-19, warranting investigation into underlying causes.

Methods

We established monitoring networks for suspected respiratory infection in 14 tertiary hospitals nationwide. PCR for SARS-CoV-2, influenza A and B were performed on 3708 respiratory specimens and deep sequencing were conducted to identify co-infections or newly emerging microbes in 2023. Viral evolutionary analysis was completed. We retrospectively detected serum antibody level for various respiratory pathogens from 4324 adults without respiratory infections over 7 years to observe its dynamic curves.

Findings

SARS-CoV-2 and influenza A were the main pathogens during outbreaks in 2023, bacterial-virus and bacterial-bacterial co-infections were most detected, but community co-infections didn't significantly increase pneumonia incidence. Different SARS-CoV-2 and influenza variants were present in different outbreaks, and no novel pathogens were found. The epidemiological patterns of influenza A, COVID-19 and etc. were altered, exhibiting characteristics of being "staggered" compared to most global regions, and potentially led to "overlapping prevalence". Binding antibody testing showed regular fluctuation, without significant decrease against common respiratory pathogens in adults. Influenza A antibody stimulation was attenuated during the 2023 outbreak.

Conclusions

"Misaligned" alteration in seasonal respiratory disease patterns possibly caused combined epidemics, leading to cases spike in China, 2023. In adults, antibody levels didn't show significant decline, but reduced immune response to influenza during 2020-2023 emphasizes the need for consistent vaccination during pandemics.

Pediatric Respiratory Syncytial Virus Hospitalizations, 2017-2023

Importance

Respiratory syncytial virus (RSV) transmission was disrupted worldwide following the COVID-19 pandemic, and further study is required to better understand these changes.

Objective

To compare observed and expected RSV hospital and intensive care unit (ICU) admission rates and characteristics of admitted children during the 2021-2022 and 2022-2023 seasons.

Design, Setting, and Participants

A population-based cohort study of all children aged younger than 5 years in Ontario, Canada, July 1, 2017, through March 31, 2023, was conducted.

Exposures

Individual and neighborhood-level sociodemographic and clinical characteristics were identified from administrative data, including age, palivizumab eligibility, complex medical conditions, rurality, and living in a marginalized neighborhood.

Main Outcomes and Measures

The main outcome was RSV-associated hospitalization. Secondary outcomes included ICU admissions, mechanical ventilation, extracorporeal membrane oxygenation, and in-hospital death. Poisson generalized estimating equations were used to model weekly age- and sex-specific hospitalization rates and estimate expected rates in the postpandemic era; adjusted rate ratios (RRs) and 95% CIs are reported.

Results

This cohort study included approximately 700 000 children per study year. Compared with prepandemic years (2017-2018, 2018-2019, and 2019-2020), the 2021-2022 RSV season peaked slightly earlier, but overall admission rates were comparable (289.1 vs 281.4-334.6 per 100 000, or approximately 2000 admissions). The 2022-2023 season peaked a month earlier and resulted in more than twice as many hospitalizations (770.0 per 100 000; n = 4977 admissions). The proportion of children admitted to an ICU in 2022-2023 (13.9%) was slightly higher than prepandemic (9.6%-11.4%); however, the population-based rate was triple the prepandemic levels (106.9 vs 27.6-36.6 per 100 000 children in Ontario). With the exception of palivizumab-eligible children, all sociodemographic and health status characteristics were associated with lower-than-expected RSV hospitalization rates in 2021-2022. In contrast, older age of patients was associated with higher-than-expected rates in 2022-2023 (ie, 24-59 months: RR, 1.90; 95% CI, 1.35-2.66).

Conclusions and Relevance

There were notable differences in RSV epidemiologic characteristics in Ontario following the COVID-19 pandemic. It is not yet clear whether and how long atypical RSV epidemics may persist. Clinicians and program planners should consider the potential for ongoing impacts to health care capacity and RSV immunization programs.

Deviations in RSV epidemiological patterns and population structures in the United States following the COVID-19 pandemic

Respiratory Syncytial Virus (RSV) is a leading cause of acute respiratory tract infection, with the greatest impact on infants, immunocompromised individuals, and older adults. RSV prevalence decreased substantially in the United States (US) following the implementation of COVID-19-related non-pharmaceutical interventions but later rebounded with abnormal seasonality. The biological and epidemiological factors underlying this altered behavior remain poorly defined. In this retrospective cohort study from 2009 to 2023 in Chicago, Illinois, US, we examined RSV epidemiology, clinical severity, and genetic diversity. We found that changes in RSV diagnostic platforms drove increased detections in outpatient settings post-2020 and that hospitalized adults infected with RSV-A were at higher risk of intensive care admission than those with RSV-B. While population structures of RSV-A remained unchanged, RSV-B exhibited a genetic shift into geographically distinct clusters. Mutations in the antigenic regions of the fusion protein suggest convergent evolution with potential implications for vaccine and therapeutic development.

Are we ready to face the next wave of RSV surge after the COVID-19 Omicron pandemic in China?

Background

China had its first wave of COVID-19 in 2020 and second wave of COVID-19 Omicron in 2022. The number of RSV cases decreased sharply in 2020 and 2022. Investigation of the resurge of RSV infections after the first wave of COVID-19 will guide us to take preventive actions before the resurge of RSV infections after the second wave of COVID-19 Omicron.

Methods

We analysed epidemiological and clinical data of 59934 patients with lower respiratory tract infections (LRTI) from a prospective long-term cohort surveillance programme in Suzhou, China, collected from February 2016 to January 2022. The annual incidence of RSV infection in children aged<16 years in 2020 and 2021 was compared with the pre-pandemic years 2016 to 2019. We also compared the clinical characteristics, and RSV-related ICU admissions between pre-pandemic years and 2021.

Results

Among children with LRTI, the positive rate of RSV increased by 70.7% in 2021 compared to the average level in the pre-pandemic years. The RSV resurge in 2021 was most prominently in children aged 2-4 years (a significant rise compared with the expected value 149.1%; 95%CI, 67.7% to 378%, P<.01). The percentage of RSV-related ICU admissions decreased in 2021 (3.2% vs 6.7%, P<0.01). The death rate of RSV infections in 2021 was 0.2%, while that in pre-pandemic years was only 0.02%. RSV-associated death in immunocompetent children (complicated by necrotizing encephalitis) was firstly occurred in 2021.

Conclusions

Our findings raise concerns for RSV control in Southeast China after the COVID-19 pandemic especially for children aged 2-4 years. Although ICU admissions were significantly reduced in this resurgence, we could not ignore the increase of RSV-associated death.