Flu Cases Rise in Shanghai and Hangzhou as Schools Order Classwide Isolation

Flu infections are increasing across Shanghai and Hangzhou as children return to school, with several primary school and kindergarten classes reportedly being sent home for isolation.

Parents in the two Chinese cities have described sudden school notices, rising absenteeism, and entire classrooms being temporarily closed after students tested positive for influenza. The reports have raised concerns about how quickly seasonal flu is spreading among children and families at the beginning of the new school term.

The situation is particularly notable because the outbreaks have emerged relatively early in the academic year, while China's main influenza transmission period generally occurs later in the autumn and winter.

School Classes Placed Under Isolation

In Hangzhou, the capital of Zhejiang Province, one parent said her third-grade daughter's class was affected only days after the start of the semester.

According to a report cited by Hangzhou News Center, the parent, identified as Li, said approximately 10 students in a class of about 40 had already gone home with fevers. Around half of those students who were tested reportedly received positive flu results.

Local health requirements then resulted in the entire class being instructed to remain at home for four days.

The class was reportedly scheduled to stay home from Sept. 11 through Sept. 14, with students expected to return on Sept. 15.

Although Li's daughter did not become infected, the incident illustrates how quickly a small number of cases can disrupt an entire classroom when health authorities require group isolation.

Similar reports have emerged from Shanghai, a major financial and commercial center located northeast of Hangzhou.

One Shanghai parent reportedly posted on social media asking what was happening with influenza in the city. The parent said the family received a notification early in the morning informing them that the entire class had been placed under quarantine. By later that day, they learned that roughly half of the students were absent because of illness.

Another case reportedly involved a kindergarten-level class in Shanghai's Baoshan district.

According to Nanjing Morning Post, a teacher sent parents a message stating that a seasonal influenza case had been confirmed. The entire class was subsequently instructed to undergo four days of isolation before returning to school.

Reports shared online have also claimed that multiple classes across Shanghai were sent home one after another, while some schools temporarily suspended classes altogether.

Children Account for a Growing Share of Hospital Patients

The increase in school infections appears to be reflected in pediatric medical facilities as well.

Dr. Qi Zhenghong, chief physician in the infectious disease department at Hangzhou Children's Hospital, told Hangzhou News Center that influenza-related outpatient visits and hospital admissions among children had increased significantly after the new semester began.

According to the doctor, flu patients previously represented only a small portion of the hospital's inpatient population. More recently, influenza cases reportedly accounted for approximately one-third of the hospital's occupied beds.

About 10 children were reportedly being admitted each day because of influenza-related illness.

Young children appear to be among those most affected. Dr. Qi said children in kindergartens and the early years of elementary school were experiencing particularly high infection rates.

The reported dominant strain is influenza A H3N2, alongside influenza B from the Victoria lineage.

Household Transmission Adds to the Concern

The spread of influenza does not necessarily stop when an infected child leaves school.

Dr. Qi described a recurring pattern in which influenza moves through households one person at a time.

In some cases, an adult becomes infected outside the home before passing the virus to a child. The child may then transmit the infection to parents or other relatives.

One example reportedly involved a grandmother who became ill before passing the virus to her 3-year-old grandson. The child developed a prolonged high fever and experienced more severe symptoms than the adults. The parents later became sick as well.

Such household chains can make controlling influenza particularly difficult.

Children can also remain ill for longer periods than adults, according to the doctor, potentially creating more opportunities for transmission within families.

For parents, this means that a single infection at school can potentially affect several members of a household.

Which Flu Strains Are Circulating?

China's National Disease Control and Prevention Administration has identified several influenza viruses as part of the strains currently circulating in the country.

These include influenza A H1N1, influenza A H3N2, and influenza B viruses from the Victoria lineage.

Influenza viruses commonly change in prevalence from one season to another. Different strains can circulate simultaneously, meaning that identifying the specific virus responsible for an individual illness generally requires appropriate testing.

Health authorities have also noted that China's influenza season typically extends from autumn through winter and into early spring.

The highest level of transmission generally occurs between November and March, although timing can vary between regions.

Northern areas typically experience a pronounced winter and spring influenza peak. Southern parts of China can also experience an additional period of influenza activity during the summer.

Is Shanghai Experiencing Flu Earlier Than Normal?

The reports of widespread classroom isolation have prompted some Shanghai parents to question whether influenza activity has started earlier than expected this year.

That question requires caution.

A rise in reported cases at the beginning of the school term does not necessarily mean that the country has entered its nationwide seasonal peak. Local outbreaks can occur before influenza activity reaches its highest level across an entire region.

Schools can also amplify transmission because children spend extended periods together indoors and have frequent close contact with classmates.

The reopening of schools after a holiday or break can therefore lead to a rapid increase in reported infections, even when broader community transmission remains difficult to assess.

For families, the immediate concern is less about predicting the exact seasonal peak and more about recognizing symptoms and taking reasonable precautions.

What Parents Should Watch For

Influenza can cause fever, cough, sore throat, fatigue, headaches, muscle aches and other respiratory symptoms. Children may also experience symptoms such as vomiting or diarrhea.

Parents should pay particular attention when a child develops a high or persistent fever, difficulty breathing, unusual drowsiness, dehydration, or symptoms that appear to worsen rather than improve.

Children with underlying health conditions may face a higher risk of complications and should be monitored particularly closely.

Families can also reduce transmission by keeping sick children home from school, following local school and health guidance, improving ventilation where practical, and practicing good hand hygiene.

Anyone concerned about a child's symptoms should seek advice from a qualified medical professional.

What Happens Next?

The reported outbreaks in Shanghai and Hangzhou highlight how quickly influenza can move through schools and households once classes resume.

The number of classroom isolation notices may fluctuate as infections rise or fall, and reports from individual schools should not automatically be interpreted as evidence of a nationwide influenza emergency.

However, the combination of increased pediatric infections, hospital admissions and classroom closures is an important development for parents and schools to monitor.

As autumn progresses, health authorities will likely continue tracking influenza activity and the strains responsible for infections.

For families in Shanghai, Hangzhou and other parts of China, the coming months could provide a clearer picture of whether the current increase represents an early seasonal rise or the beginning of a broader wave of influenza transmission.

Sources

Hangzhou News Center, Nanjing Morning Post, NetEase, and statements attributed to China's National Disease Control and Prevention Administration.

Disclaimer

This article is provided for general informational purposes only. It does not constitute medical advice, diagnosis or treatment. Influenza activity can vary by location and over time, and reports of individual school outbreaks should not be treated as representative of an entire city or country. Parents and caregivers should consult qualified healthcare professionals or local health authorities for advice about symptoms, testing, treatment and vaccination.