Impact of COVID-19 measures on the future transmission of respiratory syncytial virus

By Tarun Sai LomteMar 17 2022Reviewed by Aimee Molineux

A recent study posted to the medRxiv* preprint server discussed the impact of coronavirus disease 2019 (COVID-19) measures on the future transmission of the respiratory syncytial virus (RSV) in South Africa.

*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Background

RSV causes lower respiratory infections accounting for 5% of global deaths of children aged five years or less, and the COVID-19 pandemic has reportedly disrupted RSV circulation. A five-point alert system was constituted in March 2020 to determine the strengths of non-pharmaceutical interventions (NPI) like social distancing, use of face masks, travel bans, among others, for COVID-19 mitigation.

Implementation of NPIs had significant effects, including the decreased circulation of communicable respiratory pathogens, with a record low number of infections of RSV and influenza reported in 2020.

According to some studies, nearly every infant contracts RSV by two years, with severe infections observed in those less than six months of age. Infants get infected primarily in high-contact settings like childcare centers and schools. Moreover, reinfections are also recorded, probably due to the waning of immunity over time.

Climatic factors like low specific humidity partly drive RSV infections. Usually and unlike most temperate regions, RSV outbreak peaks in Autumn during February – June in South Africa preceding the influenza season. Throughout the COVID-19 pandemic, the implementation of NPIs has reduced the burden of endemic pathogens, leading to naïve infants who were not exposed to these pathogens.

As NPIs are being eased based on the (decreasing) prevalence of COVID-19 infections, concerns have been raised about a severe outbreak of RSV infections among those contracting the virus for the first time.

The study

The present study predicted the age structure, magnitude, and timing of the RSV outbreak in 2022 in South Africa through an epidemiological model. The researchers utilized data collected through the influenza-like illness (ILI) and severe acute respiratory illness (SARI) surveillance programs between January 2015 and August 2021.

Surveillance covered hospitals and clinics across five South African provinces. Respiratory specimens were obtained from patients through nasopharyngeal or oropharyngeal swabs and nasopharyngeal aspirates, which were tested using real-time reverse transcription-polymerase chain reaction (RT-PCR).

Data on the COVID-19 pandemic were used to assess the effects of COVID-19 preventive measures on the transmission of RSV. The authors calibrated their model to pre-COVID-19 data and estimated the impact of NPIs during 2020-21.

Subsequently, the model was run to project RSV trajectory for 2022 – 2027, considering no interventions from 2022. Further, the size of RSV peak in 2022 and total outbreak size relative to pre-COVID-19 times were estimated.

Findings

The authors found a disrupted transmission pattern of RSV because of COVID-19 NPIs. The typical RSV season in 2020 was almost entirely suppressed, but a resurgence was observed during the August – December 2020 period, coincident with the relaxation of NPIs. RSV transmission persisted in early 2021; however, the stringent NPIs implemented in response to the third COVID-19 wave reduced RSV circulation.

Age distribution of severe infections was affected due to the disrupted transmission. A 47% and 37% reduction in RSV transmission was estimated during the first and second COVID-19 lockdown periods, respectively.

According to the predicted model, an irregular and intense pattern would be observed in 2022, with a peak incidence rate in April 2022. The number of hospitalizations would increase at the peak time of the 2022 outbreak by 32% relative to that in the pre-COVID-19 period (2015-19). Their model predicted the resumption of a typical RSV seasonal pattern from 2023, assuming that schools will function without closures.

Next, the research team investigated the effects of varying lengths and intensities of NPI implementation and noted that low levels (less intense) of NPIs caused a negligible impact on predictions. But as the NPIs were implemented strictly, an intense yet smaller RSV outbreak in 2022 was predicted, increasing the buildup of naïve population and resulting in a much more severe outbreak in 2023 relative to 2022 levels.

A prolonged period of NPIs (3 years) decreased the likelihood of an intense and more extensive outbreak upon easing of NPIs, and the transmission dynamics were predicted to follow typical seasonal patterns.

Conclusions

The study predicted an intense outbreak of RSV infections in 2022, peaking in April with a 32% increase in magnitude compared to pre-COVID-19 seasons. The hospitalization burden would also increase at the peak time among all infants (<2 years), but the highest relative increase would be among those aged 6 – 23 months.

Based on the outbreak predictions for 2022, the authors suggested that hospitals take necessary precautionary measures to face a large, out-of-season RSV outbreak in April.

*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.