COVID-19 Symptoms in Infants and Young Children

It is known that COVID-19 infections in infants and young children are often mild compared to adults.
Common symptoms include
Fever, cough, runny nose, decreased appetite, and gastrointestinal symptoms (vomiting/diarrhea).
•Especially Fever is the most frequent symptom, occurring in about 77% of cases. It has been reported.
• During the Omicron variant's surge,
•Increased frequency of febrile seizuresThis has also been reported.
The duration of fever isMost are about 2-3 days.before the onset of the influenza season.

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Complications

• Relatively common complications in infants and young children are
Dehydration, poor oral intake, febrile seizures, pneumonia, etc.
• Hospitalization due to decreased appetite and dehydration is reported to be relatively common, especially in infants and young children.
However, severe cases are said to be relatively rare.

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School Attendance Guidelines

• In Japan, based on the School Health and Safety Act
You will be excluded from attendance from day 0 of symptom onset, after 5 days have passed, and 1 day after your symptoms have improved.
• Family members are not subject to isolation measures as close contacts and can continue their normal lives.

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🧠 Aftereffects

• The frequency of post-COVID-19 conditions in children is lower than in adults
According to reports from Japan, the percentage of people whose symptoms persist for 28 days or more is approximately 3.2%.
• The reported symptoms are
Cough
Fatigue
Poor concentration, etc.

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Treatment

For young children with COVID-19, symptomatic treatment is generally recommended.
Fever reducer
Hydration
・Follow-up observation, etc.
Antiviral drugs may be considered for severe cases or cases with underlying conditions.

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Literature

• Sobolewska-Pilarczyk M et al. COVID-19 Infections in Infants. Scientific Reports. 2022.

• Akaishi T et al. Coronavirus Disease 2019 Transmission and Symptoms in Young Children During the Delta and Omicron Variant Outbreaks. Journal of International Medical Research. 2022.

• Iijima H et al. Clinical Features and Outcomes of COVID-19 in Very Young Infants in Japan. Journal of Infection and Chemotherapy. 2022.

• Tachikawa J et al. Clinical Characteristics of Hospitalized Children With COVID-19 Following the Spread of the BA.5 Omicron Variant in Japan. Pediatric Infectious Disease Journal. 2025.

• Kondo R et al. Natural Course of Acute COVID-19 Among Healthy Children in a Tertiary Hospital. Pediatrics International. 2023.

• Katsuta T et al. Acute and Postacute Clinical Characteristics of COVID-19 in Children in Japan. Pediatric Infectious Disease Journal. 2023.

• Ishiwada N et al. Guidelines for the Management of Respiratory Infectious Diseases in Children in Japan 2022. Pediatric Infectious Disease Journal. 2023.

⏱️The Right Time for Testing

• The optimal time for detecting antigens varies depending on the infectious disease.
• For COVID-19 antigen tests, sensitivity is highest within 1 to 5 days of symptom onset, peaking particularly on days 3 to 5 after symptom onset.
• Immediately after the onset of symptoms, the viral load may be insufficient, which can result in a false-negative result.
Therefore, if symptoms are severe but the test is negative, retesting or a PCR test 1-2 days later is recommended.
• Since viral load peaks on the first or second day of influenza symptoms, the virus is often detectable immediately after the onset of fever or within 24 hours.
Therefore, influenza testing is recommended within 48 hours of symptom onset.

Literature

• Hayden MK, et al. The Infectious Diseases Society of America Guidelines on the Diagnosis of COVID-19: Antigen Testing. Clinical Infectious Diseases. 2024.
• Chu VT, et al. Comparison of Home Antigen Testing With RT-PCR and Viral Culture During the Course of SARS-CoV-2 Infection. JAMA Internal Medicine. 2022.
Uyeki TM, et al. Influenza. Lancet. 2022.
• Frediani JK, et al. Delayed Peak SARS-CoV-2 Viral Loads Relative to Symptom Onset. Clinical Infectious Diseases. 2024.

Scales of justice Which is heavier for a child?

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• In infants and young children, studies haveInfluenza hospitalization rates are higher than COVID-19.A tendency has been reported.
• This is particularly noticeable in children under 6 months and under 5 years old.
In the case of influenza,Type A (especially H3N2)It is considered to be prone to severe illness.
However, severe illness (ICU admission, mechanical ventilation, death) occurred in both infections.Relatively rarebetween 27 and 36 weeks of pregnancy.

Literature

• Wagenlechner C, et al. Short and Long-Term Outcomes of Children Hospitalized With COVID-19 or Influenza. Scientific Reports. 2025.
• Committee on Infectious Diseases. Recommendations for Prevention and Control of Influenza in Children 2025-2026. Pediatrics.
Havers FP, et al. COVID-19-Associated Hospitalizations Among Infants. MMWR. 2024.

👵 Which is more dangerous for the elderly?👴

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On the other hand, the situation is different for the elderly.
• The study reports a mortality rate of 16.91 TP3T among hospitalized COVID-19 patients and 5.81 TP3T among hospitalized influenza patients.
In other words, the risk of death from COVID-19 is said to be about 2.9 times higher.
• It has also been reported that COVID-19 is associated with a high incidence of severe complications such as respiratory failure, ICU admission, and sepsis.

Literature

• Piroth L, et al. Comparison of the Characteristics, Morbidity, and Mortality of COVID-19 and Seasonal Influenza. Lancet Respiratory Medicine. 2021.
• Bager P, et al. Hospital and Mortality Burden of COVID-19 Compared With Influenza. Lancet Infectious Diseases. 2025.
• Bajema KL, et al. Severity and Long-Term Mortality of COVID-19, Influenza, and RSV. JAMA Internal Medicine. 2025.

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📊 Household infection rate

Homes are places where respiratory infections can easily spread.
•Household transmission rate of COVID-19Approx. 18–211 TP3TIt has been reported.
On the other hand, with influenzaApprox. 2–71 TP3Tand COVID-19 tends to spread more easily within households.

However, depending on the circulating strain of influenza
50%: A Case of Household Transmissionhas been reported.

Literature

• Madewell ZJ, et al. Factors Associated With Household Transmission of SARS-CoV-2. JAMA Network Open. 2021.
• Thompson HA, et al. Setting-Specific Transmission Rates of SARS-CoV-2. Clinical Infectious Diseases. 2021.
• Dahlgren FS, et al. Household Transmission of Influenza A and B. Statistics in Medicine. 2021.
• Rolfes MA, et al. Household Transmission of Influenza A Viruses. JAMA. 2023