Which group of children had the highest burden of respiratory tract infections after COVID restrictions lifted?
After COVID-19 restrictions were relaxed, children began encountering respiratory viruses they had not been exposed to during lockdowns. A study in Nanjing, China, looked at which age group was hit hardest. The answer is clear: preschoolers (ages 4–6) had the highest burden, with 68.3% testing positive for a respiratory pathogen, significantly more than other age groups 3.
What the research says
A retrospective study of 7,473 children (≤18 years) with acute respiratory infections at a Nanjing hospital from January 2024 to May 2025 found an overall pathogen detection rate of 61.8% 3. Preschoolers (4–6 years) had the highest burden at 68.3%, significantly exceeding other age groups (p < 0.008) 3. The most common pathogens were rhinovirus (16.9%), Mycoplasma pneumoniae (12.4%), and respiratory syncytial virus (9.0%) 3. Co-infections occurred in 17.5% of positive samples 3.
Other studies confirm that young children are especially vulnerable to respiratory infections. A meta-analysis of risk factors for recurrent respiratory infections in preschoolers found that asthma, passive smoking, and frequent snack intake significantly increased risk 4. Additionally, RSV remains a major cause of hospitalization in children under 5, with about 3 million hospitalizations and over 100,000 deaths annually worldwide 5. In Thailand, RSV-related lower respiratory tract infections peaked in children during the rainy season, with pneumonia being the most common cause of hospitalization 7.
What to ask your doctor
- What can I do to reduce my preschooler's risk of catching respiratory infections, especially after pandemic restrictions have lifted?
- Are there any vaccines or preventive treatments recommended for my child, such as the RSV monoclonal antibody or influenza vaccine?
- How can I tell if my child's cough or cold is something more serious, like pneumonia or bronchiolitis?
- My child has asthma or is exposed to secondhand smoke — what extra precautions should we take?
- Should I be concerned about co-infections, and when should I bring my child back to the doctor if symptoms don't improve?
This question is drawn from common patient questions about this topic and answered using cited medical research. We do not provide individualized advice.