Influenza
Version: November 2025
Introduction
Influenza, commonly known as the flu, is a contagious respiratory illness caused by influenza viruses. It primarily affects the nose, throat, and lungs. The flu spreads easily through droplets from coughs or sneezes. Influenza A and B are the main types affecting humans, with seasonal epidemics occurring annually. Symptoms include fever, chills, muscle aches, sore throat, cough, and fatigue. While most recover in a few weeks, influenza can lead to severe complications, especially in vulnerable populations like the elderly, young children, and those with underlying health conditions. Vaccination is the primary prevention strategy to mitigate its impact.
Highlights
- Recent case surge: November 2025 recorded an unprecedented spike in influenza cases, with nearly 4.8 million cases, reflecting significant transmission rates.
- Low mortality rate: Although the number of cases is high, deaths remain low, suggesting effective management or a less virulent strain.
- Seasonal patterns: There is a cyclic trend, with peaks typically seen during winter months, corresponding to higher transmission rates.
- Annual fluctuations: Case numbers have varied over the years, showing pronounced peaks in recent years, indicating possible changes in virus behavior or public health responses.
Analysis
Cases Analysis
The influenza case data from Mainland China demonstrates varying patterns over a decade (2015-2025). Initially, from late 2015 to 2017, influenza case numbers show moderate seasonal peaks with typical increases during the winter months, and a notable spike in December 2017 with over 120,000 cases. However, the period from 2018 to 2019 witnessed dramatic surges, especially in January 2019, with cases peaking at over 600,000. December 2019 marked another extreme increase to nearly 1.2 million cases—indicative of an intense flu season.
An interesting deviation occurred in 2020, where influenza cases sharply declined, likely due to COVID-19 pandemic measures like social distancing which curbed the influenza transmission. Following this, beginning 2021, an upward trend resumes with significant peaks noted in March 2023 at over 3.7 million cases and December 2023, which saw over 4.1 million cases. This uptick might suggest shifts in influenza strains or lowered population immunity due to the prior dip in cases.
By 2024 and 2025, the cyclical peaks persist, with January 2024 marking high case numbers and another surge observed in November 2025 with cases nearing 4.8 million. These patterns underscore the need for ongoing influenza monitoring and enhanced public health strategies, such as vaccinations, to mitigate periodic increases in cases.
Deaths Analysis
The data from the Chinese mainland shows fluctuations in influenza cases and deaths from 2015 to 2025. A significant pattern emerges in 2019, with cases peaking at just under 1.2 million in December. This surge corresponds with increased winter deaths, notably the highest recorded in January 2019 with 143 fatalities, aligning with influenza’s typical seasonal spike during colder months. These periods usually see more transmission due to factors such as increased indoor activity and reduced immune response.
As 2020 progresses, despite high case counts in January, the death rate begins to decrease, possibly indicating improved health interventions and public health infrastructure possibly influenced by the ongoing COVID-19 pandemic. In 2023, another significant spike occurs in March, exceeding 3.7 million cases but only 38 deaths, suggesting improved treatment access or vaccine coverage, resulting in lower mortality despite high transmission rates. This could also hint at changes in virus virulence or increased population immunity.
By 2025, monthly case figures remain high, as seen with nearly 4.8 million cases in November but with minimal deaths, highlighting advancements in disease management and potentially effective health policies that facilitate better outcomes for those affected. Overall, the data underscores shifts in healthcare responses and strategies dealing with influenza in the region.