The McGill-Led Breakthrough: Unpacking the Post-Pandemic RSV Surge
A groundbreaking study from researchers at McGill University has illuminated a stark reality in Canadian pediatric care: respiratory syncytial virus (RSV) hospitalizations among children more than doubled in the 2022-23 season compared to pre-pandemic levels. Published today in the Canadian Medical Association Journal (CMAJ), the research draws from active surveillance across 13 tertiary pediatric hospitals through the Immunization Monitoring Program, ACTive (IMPACT) network, which covers over 90% of specialized pediatric beds nationwide. Led by McGill's Dr. Jesse Papenburg and first author Aariana Lopes, the findings reveal 5,362 RSV-associated admissions that season—over twice the annual average of 2,517 from 2017-2020—straining healthcare resources and underscoring the virus's enduring threat.
This surge wasn't merely a rebound; it exceeded predictions from seasonal models, peaking earlier, reaching higher intensities, and lingering longer. For McGill University Health Centre (MUHC) scientists, these data from Montreal Children's Hospital and collaborators nationwide highlight the critical role of university-driven research in tracking emerging infectious threats. As Dr. Papenburg notes, "The regional and national data collected will help guide seasonal RSV prevention strategies, reducing severe illness and easing healthcare burdens."
What is RSV and Why Does it Hit Children Hardest?
Respiratory syncytial virus (RSV), first identified in 1956, is a common RNA virus causing mild cold-like symptoms in most adults but severe lower respiratory infections like bronchiolitis and pneumonia in young children. It spreads via respiratory droplets, thriving in crowded indoor settings during fall and winter. In Canada, RSV accounts for up to 75% of bronchiolitis cases, with nearly half of infections in otherwise healthy infants.
Infants under six months face the highest risk due to immature immune systems and narrow airways. Globally, RSV leads to about 3.4 million hospitalizations and 118,000 deaths in children under five annually, per World Health Organization estimates. In Canada, pre-pandemic data showed consistent seasonal waves, but the COVID-19 era disrupted this pattern through masking, distancing, and school closures—creating an "immunity debt" where unexposed children later faced intense primary infections.
Pre-Pandemic Patterns vs. the 2022-23 Explosion
Prior McGill research in JAMA Network Open (2023) established a baseline: from 2017-2022, RSV drove substantial burden, with 49.8% of cases in infants under six months across 12 IMPACT sites. The near-absence in 2020-21 gave way to a 2021-22 uptick (3,170 admissions), but 2022-23 marked a dramatic escalation.
Key metrics: median patient age rose from 6 months (IQR 1-20) to 9 months (IQR 2-27), reflecting delayed exposures. RSV now comprised 6.8% of all pediatric admissions (up 3.5 points from 3.3%). ICU needs doubled to 1,260 cases (23.5%), with infants under six months claiming 62.1% despite only 41.5% of total admissions. Lengths of stay shortened slightly (OR 0.87 for >7 days), but raw volumes overwhelmed systems.
Age Breakdown: Infants Remain Ground Zero
While surges hit all ages—2-4-year-olds saw proportions rise from 15.5% to 21.3%—the under-six-month cohort endured outsized impact: 41.5% of hospitalizations, 62.1% of ICUs, with adjusted odds of ICU admission up 35% (OR 1.35). Older toddlers (12-23 months, 2-4 years) paradoxically had lower ICU odds, possibly due to partial prior exposures or testing biases.
This shift signals vulnerability in "pandemic babies," born during restrictions and now encountering RSV without natural immunity buildup. McGill's longitudinal data emphasizes prevention targeting neonates.
Regional Variations: A National Challenge
IMPACT's pan-Canadian scope revealed nuances: Quebec and Ontario peaked in November 2022, Saskatchewan in January 2023. Proportions jumped nationwide except Nova Scotia (non-significant). Alberta (3.4% to higher), Manitoba (4.9%), and Quebec (3.9%) showed marked rises, reflecting local social mixing resumption.
These disparities inform provincial immunization rollout, with universities like McGill bridging data gaps through collaborative networks.
Unraveling the Surge: Immunity Debt and Beyond
Researchers attribute the boom to lifted restrictions: reduced early exposures left cohorts susceptible to severe primary infections. SARIMA models confirmed anomalies—observed peaks tripled predictions. Increased testing post-pandemic may contribute, but absolute rises align with global "RSV rebound" patterns in Australia, Europe.
McGill's Dr. Lopes notes, "Public health measures delayed exposure, leading to first infections later when social activities resumed." Broader factors: population growth, better surveillance, no major RSV subtype shifts.
Healthcare Strain: ICUs and Beyond
The 2022-23 wave compounded "tripledemic" pressures from flu/COVID, with RSV filling 6.8% of beds. Over 75% cases in healthy kids amplified unpredictability. Mortality odds dipped non-significantly (OR 0.63), but volumes spiked costs—estimated $millions in ICU care alone.
Recent 2024-25 data from PHAC shows ongoing hospitalizations (5,864 since Aug 2024), though prevention tools blunt peaks.
McGill University: Leading Canada's RSV Research Charge
McGill's RI-MUHC Infectious Diseases program anchors IMPACT, with Papenburg's virology expertise driving surveillance. Co-authors span McGill's School of Population and Global Health and pediatric divisions. This builds on 2023 JAMA work, positioning McGill as RSV sentinel.
University research fuels policy: data informed NACI's 2025 universal infant immunization push. McGill trains future experts via residencies, fellowships.
- Active surveillance expertise
- Multicenter collaboration
- Translational impact on vaccines
Prevention Revolution: Nirsevimab and Maternal Vaccines
Canada's toolkit evolved: Health Canada approved nirsevimab (Beyfortus) in 2023—a long-acting monoclonal antibody for infants, 70-80% effective against hospitalization. Maternal vaccines like Pfizer's Abrysvo (RSVpreF, 2023) pass antibodies via placenta.
NACI recommends universal infant protection; Ontario hit 70% nirsevimab uptake in 2024-25, slashing hospitalizations. Challenges: supply, provincial variance, awareness. Studies show 30-70% uptake globally, with Canada advancing.Full CMAJ study details here.
Uptake Challenges and Successes in 2024-25
2024-25 surveillance: 5,864 hospitalizations to date, lower than 2022-23 peaks thanks to tools. Ontario's program protected 70% newborns; national targets aim 90%. Barriers: logistics, equity in remote areas. McGill advocates data-driven scaling.
Future Outlook: Toward RSV Elimination?
With tools, experts foresee 50-80% hospitalization drops. Ongoing trials: oral antivirals, next-gen monoclonals. Universities like McGill eye genomic surveillance for variants. Policy needs: national strategy, equity focus.
Dr. Papenburg urges, "Families should leverage local preventives—every prevented case lightens the load."
Photo by Galt Museum & Archives on Unsplash
Implications for Higher Education and Research
McGill exemplifies how Canadian universities drive public health: IMPACT's academic backbone yields actionable intel. Funding pediatric research bolsters resilience. Careers in infectious disease thrive—explore opportunities.
Stakeholders: parents vigilant, policymakers proactive, researchers vigilant.
