COVID-19 is the respiratory virus most Americans think about when they hear summer respiratory illness warnings. But the CDC's Respiratory Illnesses Data Channel identifies two different viruses — both elevated above typical summer levels and both without approved vaccines — that parents of young children need to know about right now.
The CDC's most recent respiratory data update confirms that both parainfluenza virus (PIV) and human metapneumovirus (HMPV) are circulating nationally at above-normal levels for this time of year. Both can cause serious respiratory illness in infants and young children. And most parents have never heard of HMPV.
Why This Matters
For most of the year, parents dealing with a child's respiratory illness are thinking about RSV in winter, influenza in late fall and winter, and COVID-19 year-round. The summer respiratory landscape is typically quieter.
This summer, two pathogens are defying that expectation. Understanding what both viruses do, how they differ from each other, and when a child's illness requires emergency care rather than home management gives parents something valuable: the ability to recognize and respond appropriately rather than waiting for a common virus to be misidentified as something milder.
Parainfluenza Virus: The Croup Virus
Parainfluenza virus (PIV) is the leading cause of croup in children under 5 — an infection of the upper airway and voice box that produces the characteristic barking, seal-like cough and, in more severe cases, a high-pitched breathing sound called stridor. Croup is most common in children between 6 months and 3 years of age.
Home management for mild croup: Cool night air (take the child outside for 10–15 minutes) or steam from a hot shower. Keep the child calm — agitation worsens airway swelling.
When to seek emergency care: Stridor (high-pitched sound) when the child is at rest (not just during coughing), visible difficulty breathing, skin pulling in between ribs or at the base of the throat, bluish or grayish color around the lips, fever above 104°F, or an infant under 12 months with any stridor.
Human Metapneumovirus: The Virus Parents Have Never Heard Of
HMPV is less familiar to most parents than PIV, despite being one of the most common causes of respiratory infections in children worldwide. Identified only in 2001, HMPV causes illness that ranges from mild cold-like symptoms to severe lower respiratory tract disease — including bronchiolitis (inflammation of the small airways in the lungs) and pneumonia — particularly in infants, toddlers, and immunocompromised individuals.
According to the CDC, virtually all children are infected with HMPV by age 5. But because immunity from one infection is partial, people can be reinfected throughout life, and the virus can be severe on first exposure in infants. There is currently no approved vaccine and no specific antiviral treatment — management is supportive.
Symptoms to watch for:
- Runny nose, cough, and mild fever (typical presentation in older children)
- Wheezing — a high-pitched whistling sound when breathing, especially on exhaling
- Labored breathing, with visible chest wall retractions (skin pulling in between ribs)
- Feeding difficulty in infants due to respiratory effort
- Persistent high fever
When to seek emergency care: Breathing faster than 60 breaths per minute in an infant under 2 months, or significantly faster than normal for an older child; visible work to breathe (skin pulling in with each breath); color change around the lips or fingertips; inability to drink fluids or feed; or a child who appears very ill, limp, or unresponsive.
Why Both Viruses Are Elevated Simultaneously
The current above-normal circulation of both PIV and HMPV in summer is consistent with a broader pattern that emerged from the COVID-19 pandemic: when large-scale behavioral and masking changes suppressed respiratory virus circulation in 2020–2021, those viruses' seasonal patterns were disrupted. Multiple respiratory viruses are now circulating in unusual seasonal windows as herd immunity patterns have shifted.
Neither PIV nor HMPV is circulating at crisis levels — the CDC characterizes both as elevated but declining or stable, not at surge intensity — but both are higher than expected for this time of year, and the combination matters for families with young children.
Who Faces the Greatest Risk?
- Infants under 6 months for HMPV — this age group faces the highest risk of severe bronchiolitis and respiratory failure from HMPV, similar to RSV risk patterns
- Children under 3 for PIV/croup, the classic peak-risk age for this illness
- Immunocompromised children and adults, for whom both viruses can cause unusually severe disease
- Older adults, particularly those with chronic lung conditions, for whom HMPV can cause pneumonia requiring hospitalization
- Children in daycare, summer camp, or group settings where both viruses spread easily through respiratory droplets and surface contact
What You Can Do Now
Practice consistent handwashing — both PIV and HMPV spread through respiratory droplets and contact with contaminated surfaces. Hand hygiene before and after contact with children is the primary prevention measure.
If your child develops a barking cough consistent with croup, try cool night air or steam from a shower first — but watch closely for the emergency warning signs described above.
If your infant develops wheezing or labored breathing, especially after a cold, seek medical evaluation promptly — do not wait to see if it resolves on its own.
Keep sick children home from daycare and summer camp to prevent spreading both viruses to other children.
Contact your pediatrician if you are uncertain whether your child's respiratory symptoms require evaluation — both viruses can look similar to other illnesses at first presentation.
Cost and Access: What Patients Should Know
Diagnosis of both PIV and HMPV requires laboratory testing (typically multiplex respiratory panel PCR) ordered by a clinician. Neither requires specific treatment beyond supportive care in most cases. For uninsured families, pediatric evaluation for respiratory illness is available at federally qualified health centers at reduced or no cost.
The Bottom Line
Two respiratory viruses are elevated above their normal summer levels according to the CDC's latest surveillance data: parainfluenza virus, the cause of croup, and human metapneumovirus, a virus most parents have never heard of that can cause severe bronchiolitis in infants. No vaccines exist for either. Summer daycare and camp season means concentrated exposure for young children. Parents should know what both viruses look like, practice consistent handwashing, and recognize the emergency warning signs — stridor, wheezing with labored breathing, and color changes — that mean a child needs immediate medical care.
