Flu in China: Ongoing Spread and Pediatric Insights

Influenza activity in China surged after the country lifted its strict COVID-19 controls at the end of 2022, hitting children especially hard. In Zhejiang province, the average rate of influenza-like illness roughly doubled compared to pre-pandemic years, and 2023 marked the first time China recorded two distinct winter-spring flu epidemics in a single calendar year. The patterns of who gets sick, when outbreaks peak, and which virus subtypes dominate have all shifted in ways that matter for families, clinicians, and public health planners across the country.

Why the Post-COVID Flu Surge Was So Large

During China’s prolonged period of non-pharmaceutical interventions, including lockdowns, mask mandates, and travel restrictions, seasonal influenza circulated at unusually low levels. That kept case counts down in the short term, but it also meant millions of children went years without encountering common flu strains. When restrictions lifted, the virus found a population with weakened collective immunity. In Zhejiang province, the average proportion of outpatient visits attributed to influenza-like illness jumped from about 4.4% before the pandemic to roughly 8.2% afterward.¹ In Zhengzhou, 2023 brought the highest single-year case count on record, with over 40,000 influenza diagnoses in children alone.²

A serological study provided direct biological evidence for this phenomenon. Researchers measured antibody levels in young children across multiple pathogens and found clear “immunity debt” for those born during or just before the pandemic years. The effect was strongest for pathogens that had circulated widely before COVID or that mutate rapidly, exactly as seasonal influenza does.³ Combined with persistently low vaccination rates across the country, the rebound was dramatic.

Unusual Seasonal Patterns and the Two-Peak Year

Before COVID, China’s flu season followed a reasonably predictable calendar. Northern provinces typically saw a single winter peak. Southern provinces experienced activity in spring, and mid-latitude areas often had two smaller waves. The post-pandemic period broke those expectations. In 2023, influenza A(H1N1)pdm09 drove a large spring wave, then a second epidemic arrived in autumn and winter, earlier than the historical norm. This was the first documented two-peak year in China’s modern surveillance records.⁴

In Zhejiang, the autumn epidemic entered its rapid increase phase around week 36, weeks earlier than in any pre-pandemic year.¹ In Zhengzhou, the peak shifted to February through April and then again from October to December, a pattern that had not been seen before.² These timing changes matter for vaccine campaigns, which are typically planned months in advance. If flu season starts earlier or splits into two waves, a single autumn vaccination push may not cover the full risk window.

China’s Regional Flu Geography

China is enormous, and its flu patterns vary considerably by latitude. A large spatial analysis of multi-year laboratory surveillance data identified three distinct epidemiological zones. Provinces above roughly 33°N latitude, encompassing Beijing, northern China, and the northeast, experience classic winter-only epidemics. The southernmost provinces below about 27°N, including Guangdong and parts of the tropical south, tend to peak in spring. Provinces in the middle latitudes see semi-annual cycles, with activity in both winter and summer.⁵

This geographic variation creates practical challenges. A single national vaccination timeline cannot be ideal for all regions. Southern provinces may need campaigns timed differently from northern ones, and the intermediate zones face the most complex scheduling since their populations face two risk windows per year. The post-COVID disruption to these baseline patterns has added another layer of unpredictability that surveillance systems are still working to track.

Which Children Are Getting Sick

The age profile of pediatric flu patients shifted after the pandemic. In Zhengzhou, the proportion of newborns and very young children among flu patients decreased, while the proportion of school-age children increased significantly.² A retrospective cohort study of hospitalized children with influenza A found that the median age at admission rose in the post-pandemic period to about 5.7 years, and these children presented with more respiratory symptoms including cough, sore throat, and nasal congestion. Their blood work showed lower white blood cell and platelet counts alongside elevated liver enzymes compared to children hospitalized before the pandemic.⁶

The shift toward older children likely reflects the immunity gap. Children who were toddlers during lockdowns missed the typical early-childhood exposures that build partial immunity. By the time restrictions lifted, many were school-age and encountering certain flu strains essentially for the first time. On a reassuring note, the Zhengzhou data showed that the proportion of flu patients requiring hospitalization and ICU admission actually fell in the post-pandemic period, suggesting that while more children got sick, the average case was not more severe.

Neurological Complications in Children

Influenza can occasionally cause serious brain-related problems in children, including encephalopathy and the rarer but more dangerous acute necrotizing encephalopathy (ANE). These complications are uncommon but worth understanding because early recognition matters for outcomes.

A six-year retrospective study at a single Chinese hospital found that among 2,124 children hospitalized with confirmed influenza, about 3% developed neurological complications. The median age of affected children was 4 years, and two-thirds were under 5. None had been vaccinated. The most common symptoms on admission were fever, sudden altered consciousness, convulsions, and vomiting.⁷ Outcomes differed starkly between the two conditions. Among children with the less severe form (influenza-associated encephalopathy), about two-thirds recovered fully, while a third had lasting effects and none died. Among those with ANE, only 10% recovered fully, nearly half had long-term consequences, and about 43% died.⁷

During an H3N2 outbreak in Shenzhen in mid-2022, which occurred while COVID lockdown measures were still in effect, 513 children with confirmed H3N2 were hospitalized and 97 developed neurological complications. Eighteen had encephalopathy or encephalitis, and most of those were previously healthy children with no underlying conditions. Three progressed to ANE, and two died.⁸ The fact that this outbreak hit during lockdown, when overall flu circulation was low, underscores that even isolated outbreaks can produce severe pediatric cases.

For parents and clinicians, the takeaway is that any child with flu who develops sudden confusion, repeated seizures, or persistent altered consciousness needs urgent medical attention. These neurological complications tend to appear within a day or two of fever onset, leaving a narrow window for intervention.

Co-Infections With Mycoplasma Pneumoniae

China experienced a large wave of Mycoplasma pneumoniae infections in children in 2023 and 2024, overlapping with the flu surge. When a child is infected with both influenza A and Mycoplasma pneumoniae simultaneously, the risk of developing pneumonia increases. A study of 209 co-infected children found that those older than about 6 years who had fever lasting more than four days were particularly likely to progress to pneumonia, along with children showing certain immune markers that suggested their immune response was struggling.⁹ A separate study from Gansu province confirmed that fever duration and inflammatory markers were key predictors of complications during co-infection.¹⁰

The practical message here is straightforward: a child with flu whose fever persists beyond several days, especially if a cough is worsening rather than improving, should be reassessed for a possible bacterial or atypical co-infection. Rapid tests that can simultaneously detect multiple respiratory pathogens, including influenza A, influenza B, RSV, and SARS-CoV-2, are now available and show over 99% agreement with standard reference tests in clinical samples.¹¹ These multiplex point-of-care tests can give clinicians a result in about 30 minutes, helping distinguish between viruses that may look identical at the bedside.

Antiviral Treatment Options for Children

Oseltamivir (widely known by its brand name Tamiflu) has been the standard antiviral for pediatric flu in China for years. More recently, baloxavir marboxil, a newer antiviral that works through a different mechanism, has become available. A real-world study comparing the two in Chinese children found that baloxavir shortened fever duration by roughly a day on average compared to oseltamivir, and caused far less nausea and vomiting: about 2% of children on baloxavir reported gastrointestinal side effects versus about 12% on oseltamivir.¹² For other symptoms like cough, sore throat, and nasal congestion, the two drugs performed similarly.

Baloxavir has the practical advantage of being a single-dose treatment, while oseltamivir requires twice-daily dosing for five days. For families with young children, the compliance difference can be meaningful. That said, the emergence of resistance mutations is something researchers are tracking closely. A recent genomic analysis found that a specific mutation in the hemagglutinin protein of H1N1 viruses has been increasing in frequency globally since 2019, gradually becoming the dominant variant at that position.¹³ Whether and how quickly resistance becomes clinically significant will shape treatment choices in coming seasons.

Traditional Chinese medicine formulations, particularly ma-huang-tang, have been studied as adjuncts to standard antiviral treatment. At least one study found that combining ma-huang-tang with oseltamivir shortened fever duration in children with influenza A compared to oseltamivir alone.¹⁴ TCM is widely used alongside conventional medicine in Chinese hospitals, though the evidence base for most formulations remains limited by small study sizes and inconsistent methodologies.

The Vaccination Gap

China’s influenza vaccination rates remain far lower than those in most high-income countries. The reasons are multiple: cost (seasonal flu vaccines are not covered by China’s basic public insurance for most people), limited awareness of flu severity, and logistical challenges in distributing vaccines across a vast, climatically diverse country. A phase IV trial of a novel intranasal flu vaccine in Chinese children found it prevented about 47% of laboratory-confirmed influenza cases overall, with effectiveness varying by strain: roughly 30% against H1N1, 55% against H3N2, and about 85% against B/Victoria lineage viruses.¹⁵ A needle-free option could help with uptake among children, many of whom resist injections.

Creative approaches to boosting uptake have shown promise. A trial tested a “pay-it-forward” model in which vaccinated participants could contribute a small amount to help cover the cost for someone else, creating a social chain of goodwill. Among children offered this model, 88% got vaccinated, compared to 53% in the standard-of-care arm where families simply faced the normal out-of-pocket cost.¹⁶ The effect among older adults was even more dramatic, with uptake tripling. These results suggest that cost and social motivation are bigger barriers than vaccine hesitancy in many Chinese communities.

School-Based Control Measures

Schools are major amplifiers of flu transmission among children, and China has experimented with different strategies for keeping outbreaks from spiraling. A modeling study compared two common approaches: suspending an entire class when a threshold number of students fall ill, versus isolating only symptomatic students while keeping the rest of the class in school. Both strategies reduced transmission, but symptom-based isolation was actually more effective than class suspension in primary schools.¹⁷ Keeping healthy children in school also avoids the cascade of disrupted learning and parental work loss that class suspensions create.

This finding has economic relevance. In Suzhou, the total annual societal cost of influenza in children under five was estimated at over $7 million, with outpatient visits and hospitalizations roughly equally responsible. Indirect costs, meaning lost parental productivity, accounted for more than a third of the total economic burden among outpatients, representing nearly 22,000 days of lost work annually in that city alone.¹⁸ A broader survey across Chinese cities found that the average cost of a flu-related hospitalization was about $1,500, with children under five incurring higher outpatient costs than older age groups.¹⁹ In Hong Kong, data showed that flu hospitalizations in children generated hundreds of days of school absenteeism and parental work loss per 10,000 population each year, and that the hospitalization costs alone were comparable to what universal pediatric vaccination would cost.²⁰

Avian Influenza and the Live Poultry Market Connection

Separate from the seasonal flu that circulates among people, China faces a persistent low-level threat from avian influenza viruses that spill over from birds to humans, almost always at live poultry markets. These markets, where customers select live chickens and other birds for slaughter on-site, remain common across southern China and are well-documented hotspots for avian flu virus diversity.

Surveillance at live poultry markets in Guangdong province found that environmental sampling, collecting swabs from cages, water, and processing surfaces, correlates moderately well with what is circulating in the chickens themselves. Researchers recommended collecting samples from multiple areas of the market, including holding pens, processing zones, and selling areas, to catch viruses that may have low prevalence in any single location.²¹

A three-year longitudinal study of poultry workers at live markets in Jiangsu province found serological evidence of exposure to multiple avian flu subtypes. About 1% of workers had antibodies against H7N9, roughly 2% against H9N2, and 2% against H5N1. When researchers tested the markets themselves, they detected avian influenza viruses in nearly a quarter of all samples and identified ten different viral subtypes, many of them reassortant strains with new genetic combinations.²² The high diversity of viruses circulating at these markets, and the evidence that poultry workers are regularly exposed, keeps alive the concern that a future pandemic strain could emerge from this interface between birds and humans. Seasonal flu surveillance and avian flu surveillance serve different purposes, but both feed into the broader picture of influenza risk in China.