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Long-Term Pediatric Health Consequences of China's Zero-COVID Policy: A Seven-Year Interrupted Time Series Analysis

This seven-year interrupted time series analysis of over 27 million pediatric outpatient visits reveals that China's Zero-COVID policy induced lasting shifts in child health profiles, characterized by post-reopening surges in infectious and hematologic conditions due to an immunity gap and sustained increases in musculoskeletal and congenital disorders, alongside enduring changes in healthcare-seeking behavior.

Original authors: Yuqing Feng, Jian Yang, Yu Cao, Haomin Li

Published 2026-07-09

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Yuqing Feng, Jian Yang, Yu Cao, Haomin Li

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Big Picture: A Seven-Year Health Snapshot

Imagine a giant, seven-year-long movie of children's health in Hangzhou, China. The researchers (a team from Zhejiang University) watched this movie frame-by-frame, looking at 27 million doctor visits from January 2018 to May 2025.

They wanted to see how the "Zero-COVID" policy (strict lockdowns, masks, and staying home) changed the health of kids, not just while the virus was scary, but for years after the rules were lifted. They used a special statistical tool called an "Interrupted Time Series" analysis, which is like a high-tech stopwatch that measures exactly how a timeline changes when a specific event (like a policy change) happens.

The Three Acts of the Story

The researchers divided the seven years into three distinct chapters:

The Pre-COVID Era (2018–2019): The "Normal" baseline.
The Lockdown Era (2020–late 2022): The "Zero-COVID" period where kids stayed home, schools closed, and everyone wore masks.
The Reopening Era (Late 2022–2025): When restrictions were lifted, and life started to return to normal.

The Main Findings: What Happened to the Kids?

1. The "Immunity Gap" (The Overgrown Garden)

Think of a child's immune system like a garden. Usually, weeds (viruses and bacteria) grow there, and the garden learns how to pull them out. During the strict lockdowns, the garden was completely covered with a tarp. No weeds grew because no one went outside.

When the tarp was finally lifted (Reopening), the garden was suddenly flooded with weeds. Because the kids' immune systems hadn't "practiced" fighting these common germs for years, they got sick much more often.

The Evidence: The study found a massive explosion in unspecified infections and white blood cell abnormalities right after reopening. It was as if the immune system was overwhelmed by a sudden, unexpected storm of germs it hadn't seen in years.

2. The "Muscle Surprise" (The Hidden Trigger)

One specific finding was very surprising: Myositis (a condition where muscles become inflamed and weak).

The Analogy: Imagine a car that sits in a garage for two years. When you finally drive it, the engine sputters and the brakes squeak.
The Finding: After reopening, cases of myositis didn't just spike once; they started rising immediately and kept rising over the long term. The researchers suggest that the virus itself might be acting like a hidden trigger that wakes up these muscle problems, and this effect is lasting.

3. The "Heart Mystery" (The Diluted Soup)

The study looked at heart problems. Here, the numbers told a tricky story.

The Analogy: Imagine a pot of soup. If you add a huge amount of water (millions of other sick kids returning to the hospital), the flavor of the original ingredient (heart issues) becomes less noticeable, even if the amount of that ingredient actually went up slightly.
The Finding: The total number of kids with heart complications actually went up after reopening. However, because so many other kids were also getting sick, the percentage of heart cases looked like it went down. It was a "dilution" effect.

4. The "Behavior Shift" (The Quiet Library)

Even after the lockdowns ended, the total number of kids visiting the hospital never fully bounced back to pre-pandemic levels.

The Analogy: Think of a busy library that suddenly closes for a year. When it reopens, people are still hesitant to go in. They might stay home if they feel a little sick, or they might just be used to staying home.
The Finding: Parents and kids changed their habits. They are less likely to go to the doctor for minor issues than they were before 2020. This "new normal" means the hospital sees fewer total patients, even though the disease rates for some things are higher.

The "Good" and "Bad" Lists

The researchers looked at 411 different diseases. Here is what stood out:

Things that went UP (The "Bad" List):
- Infections: Unspecified infections and white blood cell issues (The Immunity Gap).
- Skin: Contact dermatitis and other skin issues (likely due to heavy mask use and hand sanitizing).
- Muscles: Myositis (muscle inflammation).
- Congenital issues: Some birth defects and heart chamber issues showed up more often in the data, though the researchers note this might be because fewer babies were being born overall, making the existing cases look like a bigger chunk of the pie.
Things that went DOWN (The "Good" List):
- Heart complications (proportionally): As mentioned, they were diluted by the sheer volume of other patients.
- Myositis (during lockdown): Interestingly, myositis dropped significantly during the strict lockdown years, proving that the virus (or the lack of exposure to it) was the driver.
- Certain chronic issues: Conditions like hip arthritis and vitamin D deficiency dropped, likely because people weren't going to the doctor as much for non-urgent checks.

The Bottom Line

The paper concludes that the "Zero-COVID" policy was a double-edged sword. It successfully stopped the virus from spreading, but it created a "health debt."

When the restrictions were lifted, the children's health profile changed permanently. They faced a sudden wave of infections because their immune systems needed a "refresher course," and they developed new patterns of muscle and heart issues that are still lingering years later. The study warns that the pandemic's impact on children isn't just about the virus itself; it's about how the response to the virus changed the way children get sick and how they seek help for years to come.

Technical Summary: Long-Term Pediatric Health Consequences of China's Zero-COVID Policy

Problem Statement
While China's stringent "Zero-COVID" policy effectively limited SARS-CoV-2 transmission, the long-term collateral effects on pediatric health remain inadequately characterized. Although children initially appeared less vulnerable to the virus, the aggressive containment strategy fundamentally altered disease transmission dynamics and healthcare utilization patterns. Two critical phenomena emerged during the reopening phase: the "immunity gap" (rapid surges in patient numbers following reduced pathogen exposure) and altered healthcare-seeking behaviors driven by enhanced hygiene practices and prolonged lockdowns. Previous research has documented short-term impacts, but the systemic, long-term consequences for children during the reopening phase require quantification to inform post-pandemic health system preparedness.

Methodology
This study employed a seven-year interrupted time series (ITS) analysis using data from a major tertiary children's hospital in Zhejiang Province, China.

Data Source: The analysis utilized 27,437,016 outpatient visits from children aged ≤18 years spanning January 2018 to May 2025. Neoplasms (ICD-10: C00–D48) were excluded due to their cumulative onset periods.
Period Definition: The study divided the timeline into three distinct periods:
1. Pre-COVID: January 1, 2018 – December 31, 2019.
2. COVID-Control: January 1, 2020 – December 6, 2022.
3. COVID-Reopening: December 7, 2022 – May 31, 2025.
Statistical Approach:
- Changed Proportion Rate (CPR): The authors calculated the CPR ( $CPR_{i,j}$ ) to evaluate shifts in disease proportions across periods. Diseases were categorized as "stimulated" ($CPR > 5$) or "inhibited" ($0 < CPR < 0.2$).
- Generalized Additive Models (GAMs): To address non-normal distributions and over-dispersion in monthly visit counts, the authors applied GAMs with a quasipoisson distribution. The model included segmented regression to estimate immediate level changes ( $\beta_2, \beta_4$ ) and long-term monthly trend changes ( $\beta_3, \beta_5$ ) following the two policy interventions.
- Adjustments: The models adjusted for seasonal variations using Fourier terms and controlled for confounding covariates (annual population density and proportion of children in Hangzhou) using penalized splines. Autocorrelation was addressed using Generalized Additive Mixed Models (GAMM) where necessary.

Key Contributions and Results
The analysis covered 411 diseases, with 38 exhibiting significant proportional changes. The study identified distinct temporal trajectories across infectious, hematologic, musculoskeletal, and cardiovascular domains.

Immunity Gap and Infectious Diseases: Following reopening, "unspecified infectious diseases" (B99) and "white blood cell abnormalities" (R72) surged markedly.
- Unspecified Infectious Diseases: Showed a massive proportional increase ( $CPR_{reopening,pre} = 203.98$ ) and a significant positive immediate change ( $\beta_4 = 0.880, P=0.002$ ) upon reopening, though the long-term trend was negative ( $\beta_5 = -0.152, P=0.003$ ).
- White Blood Cell Abnormalities: Demonstrated a dramatic rebound, with a significant positive immediate change ( $\beta_4 = 7.350, P=0.012$ ) and a sustained positive long-term trend, suggesting persistent effects on hematopoietic and immune function.
Musculoskeletal and Congenital Conditions:
- Myositis (M60): This was the only disease exhibiting both a significant positive immediate change ( $\beta_4 = 1.129, P=0.048$ ) and a significant positive long-term monthly trend ( $\beta_5 = 0.060, P=0.049$ ) after reopening, indicating a sustained association with the post-pandemic period.
- Congenital Malformations: Conditions such as congenital musculoskeletal deformities (Q68) and cardiac chamber malformations (Q20) showed elevated proportions post-reopening, despite significant negative monthly trends. The authors attribute this to a sharper decline in the overall birth rate compared to the decline in case numbers for these specific conditions.
Healthcare-Seeking Behavior:
- Overall visit volumes in the reopening period remained below pre-pandemic baselines.
- Diseases such as ill-defined heart disease complications (I51), hyperbilirubinemia (R17), and coxarthrosis (M16) showed sustained proportional decreases, suggesting permanent shifts in healthcare-seeking behavior or improved diagnostic specificity (e.g., DRG reforms reducing nonspecific coding).
Specific Disease Trajectories:
- Contact Dermatitis (L25): Showed a massive proportional increase ($CPR = 92.02$) and a significant immediate drop upon reopening ( $\beta_4 = -0.772, P=0.023$ ), followed by a negative long-term trend.
- Temperature Regulation Disturbances (P81): Exhibited the greatest positive immediate change during the control period ( $\beta_2 = 5.322$ ) and remained elevated post-reopening.

Significance and Claims
The paper claims that the pandemic containment measures durably altered pediatric health profiles, with persistent effects extending well beyond the acute phase.

Immunity Gap Validation: The findings support the existence of an "immunity gap," evidenced by the surges in unspecified infectious diseases and white blood cell abnormalities following the relaxation of controls.
Long-Term Sequelae: The study highlights that the pandemic's impact is not limited to acute infection but includes long-term consequences in hematologic, muscular, and cardiovascular domains. Specifically, the sustained rise in myositis and white blood cell abnormalities suggests that SARS-CoV-2 and the associated containment environment may have triggered chronic or delayed pathological mechanisms.
Policy Implications: The authors argue that these findings underscore the need for sustained epidemiological surveillance and health system preparedness. They suggest that nearly 25% of the studied diseases exhibited significant long-term increases, identifying priority areas for future monitoring.
Generalizability: While the study is a single-center observation in Hangzhou, the authors posit that the core mechanisms—such as lockdown-induced behavioral changes and the universal disruption of routines—make these findings relevant to other urban populations globally. The consistency of findings (e.g., myositis and hematologic shifts) with international reports suggests these associations may transcend specific geographic boundaries.

The study concludes that while the severe acute impact of the virus is diminishing, the structural changes in pediatric health profiles necessitate ongoing attention from policymakers and health authorities to safeguard child health in the post-pandemic era.