Respiratory syncytial virus (RSV) is the most common viral pathogen that causes lower respiratory tract infection (LRTI) in children.1 Odumade et al. explain that epidemiological trends of RSV had remained consistent until the COVID-19 pandemic. RSV had distinct spikes during the months November to March in the Northern hemisphere and June to September in the Southern hemisphere. In tropical climates, RSV circulates year-round.1 However, for much of the pandemic, RSV incidence was low. Recent months have seen a surge in RSV, especially among children.
Using RSV respiratory samples collected by the University of Rochester Clinical Microbiology Laboratory from 2017 to 2022, Falsey et al. studied epidemiological trends in the upstate NY area.2 Falsey et al. grouped the cases into pre-pandemic (2017-2020) and pandemic (2020-2022) categories for comparative measure.2 Although Falsey et al.’s research focused on upstate New York and Odumade et al.’s had a global perspective, both data sets suggested that COVID-19’s social distancing and mask mandates strongly interrupted RSV patterns in 2020, leading to a significant dampening of cases for Winter 2020-Spring 2021, followed by a resurgence of cases in the summer of 2021 when restrictions loosened in many areas.1,2 Falsey et al. stated that RSV infections virtually disappeared in New York, starting April 2020 to March 2021, then as observed by Odumade et al., a spike of cases was seen in late summer 2021.1,2
The recent 2022 surge in RSV cases among children has been associated with the lifting of mask mandates and social distancing, permitting the pathogen to spread as usual but in a context of lower immunity due to relatively low exposure during the COVID-19 pandemic.2 Transmission of RSV pathogens occurs via air droplets and the handling of contaminated surfaces.3 The primary points of entry are the eyes, nose or mouth; lifting mask mandates leads to more opportunities for RSV transmission. Odumade et al. suggested other variables to explain this difference in case load. Pertaining to the surge in 2022, Odumade et al. wrote that children born during the lockdown were shown to have lower immunity against the disease.1 During the height of the pandemic in 2020, there was a shift in infection dynamics where, per patient, it was 2x-4x more likely for the host to pick up COVID-19 pathogens than RSV pathogens.1 Thus, the severe drop of RSV was also due to the competitive behavior of COVID-19, not just mask usage and social distancing.1 Since COVID-19 is now limited by functional vaccines and RSV is not, the former has a reduced grip on the population than before, permitting RSV infections to surge through children once more. Falsey et al.’s data showed not only a surge of cases in 2022, but also a disproportionate increase when compared to the pre-pandemic data.2
This difference might be driven by a more vulnerable population of children, or it could be just a correlation or coincidence. Flu-like viruses were not being studied as meticulously pre-pandemic, so data collection was not as high. Thus, it is possible that RSV cases were being underreported pre-pandemic and now are being fully reported in 2022. This could explain the startling differences in the data from pre-pandemic versus post pandemic.
The hunt for a RSV vaccine is on, but the specific formulation needs to be based on age and susceptibility. For example, pre-term infants are at the highest risk for RSV infection due to their underdeveloped immune and cardiovascular systems while children younger than two are at a higher risk than older children.1 Thus, vaccines are being developed using the following approaches: recombinant vector, subunit, particle-based, live attenuated, chimeric, nucleic acid, and monoclonal antibodies. Monoclonal antibody vaccines are being developed for infants, while live-attenuated vaccines are in the pipeline for children older than six months. Subunit vaccines are in progress to develop a maternal vaccine that protects infants. These vaccines have progressed to stage 3 of clinical trials, and a vaccine product to protect children against RSV seems promising for August 2023. 4
References
1.Odumade, Oludare A., Simon D. van Haren, and Asimenia Angelidou. “Implications of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) pandemic on the epidemiology of pediatric respiratory syncytial virus infection.” Clinical Infectious Diseases 75.Supplement_1 (2022): S130-S135.
2.Falsey, Ann R., et al. “Perturbations in Respiratory Syncytial Virus Activity During the SARS-CoV-2 Pandemic.” The Journal of Infectious Diseases (2022).
3.Lighter, Jennifer L. & Chopra, Arun. “RSV Is Spreading Among Children—Here’s Why & When to See a Doctor.” https://nyulangone.org/news/rsv-spreading-among-children-heres-why-when-see-doctor
4.Mazur, Natalie I., et al. “Respiratory syncytial virus prevention within reach: the vaccine and monoclonal antibody landscape.” The Lancet Infectious Diseases (2022).