Winter is here (but not without viruses)

The winter season often brings a surge in respiratory illnesses driven by various viruses. Among these, SARS-CoV-2, the cause of COVID-19, and influenza have garnered global attention due to their significant health and societal impact. Meanwhile, human metapneumovirus (hMPV), although contributing to seasonal respiratory infections, presents comparatively lower risks in terms of transmissibility, severity, and complications.

Modes of Transmission

Respiratory viruses primarily spread through droplets released during coughing, sneezing, or speaking.

• SARS-CoV-2: Known for its high transmissibility, it has an R₀ of 2–6, varying by variant, allowing one individual to infect multiple others.

• Influenza: Moderately contagious, with an R₀ of 1.3–2.0, it can still overwhelm healthcare systems during seasonal outbreaks.

• hMPV: Exhibits a lower R₀ of 1.0–1.5, leading to more localized outbreaks that predominantly affect young children and the elderly.

Symptoms and Severity

While symptoms overlap, the potential severity differs significantly:

• SARS-CoV-2: Ranges from mild fever and cough to severe pneumonia, acute respiratory distress syndrome (ARDS), and multi-organ failure.

• Influenza: Causes abrupt fever, muscle aches, and fatigue; complications like pneumonia and myocarditis can occur in high-risk groups.

• hMPV: Milder symptoms like nasal congestion, wheezing, and cough are common; severe cases like bronchiolitis or pneumonia are rare and occur in vulnerable individuals.

Populations at Risk

The risk profiles vary across the three viruses:

• SARS-CoV-2: A significant threat to older adults, immunocompromised individuals, and those with chronic illnesses.

• Influenza: Particularly harmful to young children, the elderly, and pregnant women.

• hMPV: While affecting similar groups, most cases are mild, and hospitalizations are less frequent.

Complications

The complications underscore why SARS-CoV-2 and influenza are of greater concern:

• SARS-CoV-2: Severe pneumonia, blood clots, long COVID, and organ failure.

• Influenza: Bacterial pneumonia, myocarditis, and encephalitis in vulnerable populations.

• hMPV: Rarely causes severe outcomes, with complications generally limited to bronchiolitis or pneumonia in specific groups.

Public Health Impact

The transmissibility of a virus directly correlates with its public health implications:

• SARS-CoV-2: Demonstrated explosive global outbreaks during the pandemic.

• Influenza: Causes significant yearly morbidity and mortality despite its lower transmissibility.

• hMPV: Limited spread and localized impact make it less concerning from a public health perspective.

Prevention and Treatment

Preventive measures are essential across all three viruses, with greater urgency for SARS-CoV-2 and influenza:

• SARS-CoV-2: Vaccination, mask usage, ventilation, and hand hygiene are critical; antivirals like remdesivir aid in treatment.

• Influenza: Annual vaccination is key, supported by antiviral medications like oseltamivir.

• hMPV: While lacking a vaccine, good hygiene practices and avoiding contact with sick individuals suffice for prevention. Most cases require supportive care.

Conclusion

While hMPV plays a role in seasonal respiratory infections, its overall impact pales compared to SARS-CoV-2 and influenza. SARS-CoV-2 continues to dominate in transmissibility and severity, with long-lasting effects on healthcare systems and economies. Influenza remains a formidable threat with its annual toll. hMPV, though noteworthy for specific groups, typically causes milder illness and limited public health challenges.

By understanding these differences, we can better prioritize prevention and treatment efforts to safeguard our health this winter.

(The writer is a, Medical Director, International SOS)