Use of mathematical modelling to assess respiratory syncytial virus epidemiology and interventions: a literature review

Respiratory Syncytial Virus: A Narrative Review of Updates and Recent Advances in Epidemiology, Pathogenesis, Diagnosis, Management and Prevention

Respiratory syncytial virus (RSV) continues as the major cause of acute lower respiratory tract infections in children around the world, and its substantial morbidity, particularly among infants and high-risk children, poses a significant burden on healthcare systems worldwide. RSV infections occur as a spectrum, ranging from mild upper respiratory symptoms to severe bronchiolitis and pneumonia, and the number of infections shows seasonal variations in different latitudes, as well as lasting impacts, reflecting the COVID-19 pandemic. The pathogenesis of the virus involves epithelial cell invasion and/or fusion to form syncytia, along with exaggerated immune-mediated responses. Disease severity is known to depend on viral load, strain variation, and host immune immaturity. Severe RSV infection during infancy is notably linked with long-term respiratory sequelae such as recurrent wheezing and asthma. Diagnosis is based on clinical suspicion and laboratory confirmation using rapid antigen testing or nucleic acid amplification tests, namely PCR. Non-pharmaceutical interventions, maternal vaccination, and prophylaxis with monoclonal antibodies, e.g., palivizumab and nirsevimab, a newly introduced long-acting agent, are efficient protective and preventive measures. Treatment is still, for the most part, supportive in nature and focuses on oxygen supplementation, hydration, and respiratory support for patients with more severe disease courses; however, the development of immunoprophylaxis and vaccine candidates shows promise for reducing the global burden of RSV.

Impact of COVID-19 control measures on respiratory syncytial virus and hand-foot-and-mouth disease transmission in Hong Kong and South Korea

The public health and social measures (PHSMs) for mitigation/control of COVID-19 pandemic influenced the transmission dynamics of many other infectious diseases, including respiratory syncytial virus (RSV) infection, and hand, foot and mouth disease (HFMD) and their disease-burden. This study aimed to infer the transmission dynamics of these respiratory viruses and assess the impact of COVID-19 PHSMs on their community activity. We developed a compartmental framework to infer the transmission dynamics of RSV and HFMD in Hong Kong and South Korea from January 2014 to May 2024. We assessed the impact of PHSMs by comparing the change in virus transmissibility, reproduction number and population susceptibility before, during, and after the COVID-19 pandemic period. A significant reduction in RSV and HFMD activity was observed starting in January 2020, with a resurgence since late 2021. Transmissibility of both diseases decreased by 46 % - 95 % during the lull, while population susceptibility was estimated to increase by maximum of 19 %. On relaxation of the PHSMs, the transmissibility were recovered up to 70 % in Hong Kong and nearly 100 % in South Korea in 2023 with significant epidemics for these viruses. Strict implementation of COVID-19 PHSMs led to low RSV and HFMD activity, but the absence of community infection resulted in reductions in population immunity, and slightly larger epidemics when these diseases re-emerged following the COVID-19 pandemic.

Respiratory Syncytial Virus and US Pediatric Intensive Care Utilization

Importance

Bronchiolitis is the most common diagnosis necessitating respiratory support and pediatric intensive care, and respiratory syncytial virus (RSV) is the most common cause of bronchiolitis. In 2023, the monoclonal antibody nirsevimab and the maternal RSVpreF vaccine were implemented to prevent RSV in infants.

Objective

To determine the potential association of novel RSV prevention strategies with pediatric intensive care unit (ICU) utilization.

Design, Setting, and Participants

This retrospective cross-sectional study examined US pediatric ICU encounters with and without RSV from January 1, 2017, to June 1, 2023. Data were from Oracle Cerner RealWorld Data, a national electronic health record database. All children (aged >1 day and <18 years) admitted to an ICU during the study period were included in the analysis. Statistical analysis was performed from February to May 2024.

Main Outcomes and Measures

The primary outcomes were ICU encounters with RSV and ICU encounters with RSV eligible for RSV prevention.

Results

There were 119 782 ICU encounters from 53 hospitals; 65 757 encounters (54.9%) were male; median (IQR) age was 4.5 (1.1-12.5) years, median (IQR) ICU length of stay was 1.8 (1.0-3.9) days; 13 702 ICU encounters (11.4%) had RSV, of which 38.6% (5217) were eligible for prevention (4.4% of total ICU encounters). Encounters with RSV accounted for 21.1% (109 334) of ICU days, of which 43.8% (47 888) were eligible for prevention (9.2% of total ICU days). Encounters with RSV were associated with a greater use of positive pressure ventilation (4074 [29.7%] vs 18 821 [17.7%]; P < .001) and vasoactive medications (3057 [22.3%] vs 18 570 [17.5%]; P < .001) compared with those without RSV.

Conclusions and Relevance

The findings of this retrospective cross-sectional study of RSV and US pediatric intensive care utilization suggest that if 65% to 85% of eligible children received RSV prevention, an estimated 2.1% to 2.8% reduction in pediatric ICU encounters and an estimated 4.5% to 5.9% reduction in pediatric ICU days could be achieved.

Long-term effects of non-pharmaceutical interventions on total disease burden in parsimonious epidemiological models

The recent global COVID-19 pandemic resulted in governments enacting non-pharmaceutical interventions (NPIs) targeted at reducing transmission of SARS-CoV-2. But the NPIs also affected the transmission of viruses causing non-target seasonal respiratory diseases, including influenza and respiratory syncytial virus (RSV). In many countries, the NPIs were found to reduce cases of such seasonal respiratory diseases, but there is also evidence that subsequent relaxation of NPIs led to outbreaks of these diseases that were larger than pre-pandemic ones, due to the accumulation of susceptible individuals prior to relaxation. Therefore, the net long-term effects of NPIs on the total disease burden of non-target diseases remain unclear. Knowledge of this is important for infectious disease management and maintenance of public health. In this study, we shed light on this issue for the simplified scenario of a set of NPIs that prevent or reduce transmission of a seasonal respiratory disease for about a year and are then removed, using mathematical analyses and numerical simulations of a suite of four epidemiological models with varying complexity and generality. The model parameters were estimated using empirical data pertaining to seasonal respiratory diseases and covered a wide range. Our results showed that NPIs reduced the total disease burden of a non-target seasonal respiratory disease in the long-term. Expressed as a percentage of population size, the reduction was greater for larger values of the basic reproduction number and the immunity loss rate, reflecting larger outbreaks and hence more infections averted by imposition of NPIs. Our study provides a foundation for exploring the effects of NPIs on total disease burden in more-complex scenarios.

Modelling respiratory syncytial virus age-specific risk of hospitalisation in term and preterm infants

BACKGROUND

Respiratory syncytial virus (RSV) is the most common cause of acute lower respiratory infections in children worldwide. The highest incidence of severe disease is in the first 6 months of life, with infants born preterm at greatest risk for severe RSV infections. The licensure of new RSV therapeutics (a long-acting monoclonal antibody and a maternal vaccine) in Europe, USA, UK and most recently in Australia, has driven the need for strategic decision making on the implementation of RSV immunisation programs. Data driven approaches, considering the local RSV epidemiology, are critical to advise on the optimal use of these therapeutics for effective RSV control.

METHODS

We developed a dynamic compartmental model of RSV transmission fitted to individually-linked population-based laboratory, perinatal and hospitalisation data for 2000-2012 from metropolitan Western Australia (WA), stratified by age and prior exposure. We account for the differential risk of RSV-hospitalisation in full-term and preterm infants (defined as < 37 weeks gestation). We formulated a function relating age, RSV exposure history, and preterm status to the risk of RSV-hospitalisation given infection.

RESULTS

The age-to-risk function shows that risk of hospitalisation, given RSV infection, declines quickly in the first 12 months of life for all infants and is 2.6 times higher in preterm compared with term infants. The hospitalisation risk, given infection, declines to < 10% of the risk at birth by age 7 months for term infants and by 9 months for preterm infants.

CONCLUSIONS

The dynamic model, using the age-to-risk function, characterises RSV epidemiology for metropolitan WA and can now be extended to predict the impact of prevention measures. The stratification of the model by preterm status will enable the comparative assessment of potential strategies in the extended model that target this RSV risk group relative to all-population approaches. Furthermore, the age-to-risk function developed in this work has wider relevance to the epidemiological characterisation of RSV.

Comparison of a static cohort model and dynamic transmission model for respiratory syncytial virus intervention programs for infants in England and Wales

BACKGROUND

A recent study comparing results of multiple cost-effectiveness analyses (CEAs) in a hypothetical population found that monoclonal antibody (mAb) immunoprophylaxis for respiratory syncytial virus (RSV) in infants averted fewer medically attended cases when estimated using dynamic transmission models (DTMs) versus static cohort models (SCMs). We aimed to investigate whether model calibration or parameterization could be the primary driver of inconsistencies between SCM and DTM predictions.

METHODS

A recently published DTM evaluating the CEA of infant mAb immunoprophylaxis in England and Wales (EW) was selected as the reference model. We adapted our previously published SCM for US infants to EW by utilizing the same data sources used by the DTM. Both models parameterized mAb efficacy from a randomized clinical trial (RCT) that estimated an average efficacy of 74.5% against all medically attended RSV episodes and 62.1% against RSV hospitalizations. To align model assumptions, we modified the SCM to incorporate waning efficacy. Since the estimated indirect effects from the DTM were small (i.e., approximately 100-fold smaller in magnitude than direct effects), we hypothesized that alignment of model parameters should result in alignment of model predictions. Outputs for model comparison comprised averted hospitalizations and averted GP visits, estimated for seasonal (S) and seasonal-with-catchup (SC) immunization strategies.

RESULTS

When we aligned the SCM intervention parameters to DTM intervention parameters, significantly more averted hospitalizations were predicted by the SCM (S: 32.3%; SC: 51.3%) than the DTM (S: 17.8%; SC: 28.6%). The SCM most closely replicated the DTM results when the initial efficacy of the mAb intervention was 62.1%, leading to an average efficacy of 39.3%. Under this parameterization the SCM predicted 17.4% (S) and 27.7% (SC) averted hospitalizations. Results were similar for averted GP visits.

CONCLUSIONS

Parameterization of the RSV mAb intervention efficacy is a plausible primary driver of differences between SCM versus DTM model predictions.

The Path Towards Effective Respiratory Syncytial Virus Immunization Policies: Recommended Actions

The respiratory syncytial virus (RSV) causes a substantial burden worldwide. After over six decades of research, there is finally a licensed immunization option that can protect the broad infant population, and other will follow soon. RSV immunization should be in place from season 2023/2024 onwards. Doing so requires thoughtful but swift steps. This paper reflects the view of four immunization experts on the efforts being made across the globe to accommodate the new immunization options and provides recommendations organized around five priorities: (I) documenting the burden of RSV in specific populations; (II) expanding RSV diagnostic capacity in clinical practice; (III) strengthening RSV surveillance; (IV) planning for the new preventive options; (V) achieving immunization targets. Overall, Spain has been a notable example of converting RSV prevention into a national desideratum and has pioneered the inclusion of RSV in some of the regional immunization calendars for infants facing their first RSV season.

RSV through the COVID-19 pandemic: Burden, shifting epidemiology, and implications for the future

Respiratory syncytial virus (RSV) represents a major global healthcare burden, particularly in those under 5 years of age. There is no available vaccine, with treatment limited to supportive care or palivizumab for high-risk children. Additionally, although a causal relationship has not been established, RSV has been associated with the development of asthma or wheezing in some children. The COVID-19 pandemic and the introduction of nonpharmaceutical interventions (NPIs) have caused substantial changes to RSV seasonality and epidemiology. Many countries have experienced an absence of RSV during the time of a typical season, followed by an out-of-season surge upon relaxation of NPI use. These dynamics have disrupted traditional RSV disease patterns and assumptions, but also provide a unique opportunity to learn more about the transmission of RSV and other respiratory viruses, as well as inform future approaches to RSV preventive strategies. Here, we review the RSV burden and epidemiology through the COVID-19 pandemic and discuss how new data may affect future decisions regarding RSV prevention.