Influenza A and B infections in children are clinically similar in presentation and severity, with no consistent differences in symptoms, disease duration, or outcomes, though some studies suggest subtle variations in specific manifestations and age distribution.
Clinical Presentation
The clinical presentations of influenza A and B are largely indistinguishable. Both types cause acute onset of fever, cough, rhinitis, sore throat, headache, myalgia, and malaise. Children are more likely than adults to experience gastrointestinal symptoms including nausea, vomiting, diarrhea, and abdominal pain with both influenza types. Common clinical syndromes include nonspecific febrile illness, bronchiolitis, croup, or pertussis-like illness.
Some studies have identified minor differences: influenza B patients may more frequently present with pharyngitis, acute otitis media, and stenosing laryngotracheitis. However, no single symptom reliably distinguishes between the two types. Fever duration (approximately 4 days) and total illness duration (7-10 days) are similar for both types.
Age Distribution
Influenza B tends to affect older children, with mean ages of 5.6 years for influenza B versus 4.1 years for influenza A in one study. Children aged 5-14 years are more than twice as likely to be infected with influenza B compared to younger children.
Severity and Complications
Contrary to traditional assumptions, influenza B is not milder than influenza A. Both types cause similar rates of hospitalization, ICU admission, and complications. One Canadian study found mortality was actually higher with influenza B (1.1%) compared to influenza A (0.4%). Neurologic complications (8-11% of hospitalized children), bacterial complications including otitis media and pneumonia, and other serious complications occur with both types.
Testing and Clinical Diagnosis
For most outpatients during periods of high influenza activity, influenza is a clinical diagnosis. Rapid influenza diagnostic tests (RIDTs) have moderate sensitivity (≈50–70%) and very high specificity (>98%) compared with RT-PCR, meaning a positive test is reliable but a negative test does not rule out influenza. Pooled sensitivity is approximately 54% for influenza A and 53% for influenza B, with better performance in children than adults. Even then, up to one-third to one-half of true influenza cases will test negative, particularly during peak season. In contrast, rapid molecular assays demonstrate substantially higher sensitivity (≈92–95%) with similarly high specificity and are preferred when testing is necessary, especially for hospitalized or high-risk patients.
During influenza season, clinical diagnosis without testing is appropriate when results will not change management. Fever with cough or sore throat has a positive predictive value ranging from 30–88%, depending on community prevalence. The Infectious Diseases Society of America supports empiric antiviral treatment (if you decide to do that) based on clinical diagnosis when testing is unavailable or unlikely to influence care. Testing is most useful when results will alter treatment decisions, guide infection control, or help differentiate influenza from other circulating respiratory pathogens, including SARS-CoV-2. For otherwise healthy, well-appearing children presenting early in illness with classic symptoms during peak influenza activity, empiric management (with or without antivirals) without testing avoids false reassurance, unnecessary cost, and delays in care.
Management
Management is identical for both influenza types. Supportive care remains the cornerstone of influenza management in children and includes adequate hydration, antipyretics such as acetaminophen or ibuprofen, rest, and symptom-directed care for cough and congestion. Aspirin should be avoided due to the risk of Reye syndrome. Caregivers should be counseled to seek urgent medical evaluation for signs of clinical deterioration, including persistent or worsening respiratory distress, hypoxia, dehydration or inability to tolerate oral fluids, altered mental status, severe or persistent vomiting, chest pain, or concern for secondary bacterial infection such as focal lung findings or recurrent fever after initial improvement. Infants, children with chronic medical conditions, immunocompromised patients, and those with poor social support should have a lower threshold for re-evaluation, as should any child who appears toxic or whose caregiver feels something is “not right.”
Regarding antivirals, American Academy of Pediatrics recommends oral oseltamivir as the antiviral drug of choice for both influenza A and B in children, including hospitalized patients. All neuraminidase inhibitors (oseltamivir, zanamivir, peramivir) and baloxavir have activity against both influenza A and B viruses. Treatment should be initiated as soon as possible if you’re going to prescribe, ideally within 48 hours of symptom onset, for children with severe disease, those at high risk for complications (including all children <5 years), and hospitalized patients.
In otherwise healthy children with uncomplicated influenza, the clinical benefit of oseltamivir is modest. Meta-analyses of randomized trials show that when started within 48 hours of symptom onset, oseltamivir shortens illness duration by approximately 18 hours overall and by about 30 hours in children without asthma, without reliably preventing return visits or eliminating symptoms. While oseltamivir reduces the risk of otitis media by roughly 30–35%, it is also associated with increased vomiting, particularly in children. When weighed against medication cost, potential side effects, and the self-limited nature of influenza in most healthy children, these modest benefits support a selective, risk-based approach rather than routine prescribing for all well-appearing pediatric patients.
References and Key Findings
- Subtype-Specific Clinical Presentation, Medical Treatment and Family Impact of Influenza in Children 1–5 Years of Age Treated in Outpatient Practices in Germany During Three Postpandemic Years, 2013–2015.Streng A, Prifert C, Weissbrich B, et al. Pediatr Infect Dis J. 2018;37(9):861–867.
Found no clinically meaningful differences in symptom profile, illness duration, or outpatient management between influenza A and B in young children. - Striking Similarities in the Presentation and Duration of Illness of Influenza A and B in the Community: A Study Based on Sentinel Surveillance Networks in France and Turkey, 2010–2012.Cohen JM, Silva ML, Caini S, et al. PLoS One. 2015;10(10):e0139431.
Demonstrated near-identical symptom patterns and illness duration for influenza A and B across large community surveillance cohorts. - Clinical Similarities Between Influenza A and B in Children: A Single-Center Study, 2017/18 Season, Korea.Oh YN, Kim S, Choi YB, et al. BMC Pediatrics. 2019;19(1):472.
Showed no significant differences in clinical presentation, fever duration, or outcomes between influenza A and B in hospitalized and outpatient children. - Comparative Severity of Influenza A and B Infections in Hospitalized Children.Mattila JM, Vuorinen T, Heikkinen T. Pediatr Infect Dis J. 2020;39(6):489–493.
Found similar hospitalization severity, ICU use, and complication rates between influenza A and B, challenging the belief that influenza B is milder. - Clinical Characteristics Are Similar Across Type A and B Influenza Virus Infections.Mosnier A, Caini S, Daviaud I, et al. PLoS One. 2015;10(9):e0136186.
Confirmed that influenza A and B infections have overlapping clinical features and severity across age groups. - Influenza.Szablewski C, Daugherty M, Azziz-Baumgartner E. CDC Yellow Book.
Provides authoritative epidemiology, transmission, and management guidance, emphasizing that clinical illness does not reliably differ by influenza type. - Recommendations for Prevention and Control of Influenza in Children, 2025–2026: Technical Report.Committee on Infectious Diseases. Pediatrics. 2025;202846.
Recommends identical antiviral treatment strategies for influenza A and B and prioritizes therapy for high-risk and hospitalized children. - Recommendations for Prevention and Control of Influenza in Children, 2023–2024.Committee on Infectious Diseases. Pediatrics. 2023;152(4):e2023063773.
Reinforces oseltamivir as first-line therapy for both influenza types and supports early treatment in high-risk pediatric patients. - Hospitalization for Influenza A Versus B.Tran D, Vaudry W, Moore D, et al. Pediatrics. 2016;138(3):e20154643.
Found comparable hospitalization rates and, in some analyses, higher severity markers associated with influenza B. - Recommendations for Prevention and Control of Influenza in Children, 2022–2023.Committee on Infectious Diseases. Pediatrics. 2022;150(4):e2022059275.
Supports consistent antiviral indications across influenza types and emphasizes risk-based prescribing rather than subtype.
