How great is the potential health threat from influenza complications?

The recent news that 48-year-old actress Barbie Hsu (Big S) and 41-year-old media person Ng Yu-yan died of influenza was so shocking. While we feel sorry and sad for them, it also reminds us once again the severity of the disease influenza and its potential threat to health.

Now let's talk about influenza.

01. Why does influenza cause death?

Many people still don’t pay enough attention to influenza, and this seemingly common disease can often lead to significant losses. According to WHO estimates, influenza causes 3 million to 5 million severe cases and 290,000 to 650,000 respiratory disease-related deaths worldwide each year [1]. This is a considerable number, and it can affect people of all ages.

Why does influenza cause death? It is mainly because influenza triggers a series of other diseases.

1. Complications. Influenza infection can cause complications that affect health, a typical example being pneumonia, which is the most common serious complication of influenza. If lung inflammation is not treated in time or the treatment strategy is wrong or it cannot be treated, it will be troublesome.

For example, based on the national emergency influenza-like cases and influenza etiology testing data, the average number of excess emergency cases for influenza in my country is 3.005 million (95% CI: 2.165 million to 3.912 million), the number of hospitalizations for severe acute respiratory infections is 2.346 million (95% CI: 1.857 million to 2.887 million), and the average number of excess deaths from respiratory diseases is 92,000 (95% CI: 75,000 to 112,000) [2]. Of course, this also includes problems such as encephalitis and multiple organ failure.

2. For people with underlying diseases, influenza can aggravate the underlying diseases. For example, respiratory diseases such as chronic obstructive pulmonary disease (COPD) and asthma can be aggravated by influenza, leading to increased risks of complications such as dyspnea and lung infection. Cardiovascular diseases and immune system diseases also have corresponding risks.

02. Which groups are susceptible and high-risk?

Which groups are susceptible and high-risk?

1. People over 60 years old, children, and pregnant women. Children are very susceptible to influenza because their immune system is not yet fully developed. Many studies have confirmed that the incidence of influenza is highest among children. Moreover, children's symptoms vary. About 20% to 40% of symptomatic children may experience influenza-like symptoms (fever, cough or sore throat), while the proportion of asymptomatic children can range from 14% to more than 50% [3].

Therefore, influenza is also one of the important factors leading to death in children. It is estimated that about 28,000 children under the age of 18 die from influenza-related lower respiratory tract infections each year, most of which occur in children under the age of 4. The elderly are also a high-risk group for influenza due to decreased immunity and underlying diseases. A large number of studies at home and abroad have confirmed that pregnant women have a higher risk of severe illness, death and adverse pregnancy outcomes after contracting influenza.

2. People with one or more chronic diseases. People with cardiovascular disease, chronic respiratory disease, liver and kidney dysfunction, blood disease, nervous system disease, neuromuscular dysfunction, metabolic disease (including diabetes), immunosuppressive disease or low immune function are at risk of influenza.

3. Medical staff, elderly care institutions, long-term care institutions, welfare homes and other places where people gather, vulnerable groups and employees.

03. How to prevent influenza?

Influenza is common and serious, so it is also a matter of great concern in the world. In fact, every year, both the WHO and the disease control departments of various countries have special plans to deal with influenza. For example, every year the World Health Organization will work with national influenza centers and reference laboratories around the world to form a global influenza monitoring network. Laboratories and institutions in various places continue to collect influenza virus samples and analyze them.

What to do? Vaccine. All collected influenza virus samples will be combined to analyze which strains are currently circulating, their genetic mutations, antigenic characteristics, and future developments.

Based on comprehensive analysis of multiple data, the viruses that will be prevalent in the future are given. For example, the strains that will be prevalent in 2024-2025 are as follows:

Countries can then produce vaccines in advance to prevent the disease. In fact, vaccination is the best way to deal with influenza recommended by the WHO, and the WHO's goal for global influenza vaccines is 75%.

But in reality, this goal is still far away.

Finally, let me share a little-known fact: Have you heard of the Spanish flu? This flu has not actually ended. Almost all influenza A viruses today are descendants of the 1918 flu virus, including drift type H1N1, recombinant types H2N2, and H3N2. It can be said that the 1918 flu is the mother of all influenza viruses [4].

1. Iuliano AD, Roguski KM, Chang HH, et al. Estimates of global seasonal influenza-associated respiratory mortality: a modeling study [J]. Lancet, 2018, 391(10127): 1285-300. DOI:10.1016/S0140-6736(17)33293-2.

2. Gong Hui, Shen Xin, Yan Han, et al. Estimation of seasonal influenza disease burden in China from 2006 to 2019[J]. Chinese Medical Journal, 2021, 101(08): 560-7. DOI:10.3760/cma.j.cn112137-20201210-03323.

3. Uyeki TM, Hui DS, Zambon M, et al. Influenza [J]. Lancet, 2022, 400(10353): 693-706. DOI:10.1016/S0140-6736(22)00982-5.

4. Taubenberger, Jeffery K., and David M. Morens. "1918 Influenza: the mother of all pandemics." Revista Biomedica 17, no. 1 (2006): 69-79.

5. TWG, Influenza Vaccination, National Immunization Advisory Committee, and Technical Working Group. "Technical Guidelines for Influenza Vaccination in China (2023-2024)." Chinese Journal of Epidemiology 44.10 (2023): 1507-1530.