Influenza A virus is one type of virus that causes the flu. Other types include Influenza B and the rarer Influenza C. Influenza A is highly contagious, and its symptoms are more severe than the common cold. Influenza A viruses can be further divided into different subtypes. They can undergo genetic changes through recombination to form different strains, such as H3N2 and H1N1, which is commonly known as swine flu.¹
When is Flu Season in Hong Kong?
Hong Kong’s flu season typically occurs from January to March/April and again in July to August each year.² Generally, the flu peak season lasts for 8–12 weeks. However, if there is a shift in the predominant circulating virus strain, the duration of the flu season may be extended.
For example, the 2023/24 winter flu season, which began in early January 2024, initially saw the dominant circulating strain as Influenza A H3 virus. From April onwards, the main virus shifted to Influenza A H1 virus, extending the flu season to 28 weeks.
As for the 2024/25 winter flu season, which started on January 9, 2025, the currently detected influenza viruses are mainly Influenza A H1 viruses.³
| Flu Type | Influenza A | Influenza B |
| Common Hosts | Wild birds, poultry (e.g., chickens, ducks), pigs, humans | Humans |
| Transmission Routes | Droplet transmission, contact transmission (e.g., contact with poultry, patient secretions, viruses on object surfaces)4 | Droplet transmission, contact transmission (e.g., patient secretions, viruses on object surfaces), aerosol transmission5 |
| Common Symptoms | Fever, cough, fatigue, body aches, headache, etc.⁴ | Fever, cough, fatigue, shortness of breath, respiratory symptoms, etc.⁶ |
| Incubation Period | Approximately 1–4 days, average 2 days⁷ |
Is Influenza A or Influenza B More Likely to Cause Epidemics?
According to a medical article published in the academic journal PLoS ONE, Influenza A is more likely to cause pandemics than Influenza B. Research from the article indicates that 75% of seasonal influenza cases are caused by Influenza A, with the remaining 25% caused by Influenza B. Moreover, Influenza A can be further subdivided into various subtypes, making it more prone to antigenic variation, which increases the likelihood of global pandemics.⁸
Unlike the common cold, Influenza A usually has a sudden onset and is accompanied by the following symptoms: ⁹
- Cough
- Runny or stuffy nose
- Sneezing
- Sore throat
- Fever
- Headache
- Fatigue
- Chills
- Body aches
If left untreated, the flu can lead to the following complications: ⁹
- Ear infection
- Diarrhea
- Nausea
- Vomiting
- Dizziness
- Abdominal pain
- Chest pain
- Asthma attack
- Pneumonia
- Bronchitis
- Heart problems, such as myocarditis or pericarditis
- Encephalitis
- Encephalopathy
In addition to the above complications, the most severe outcome of Influenza A can be death.
Who is More Susceptible to Complications?
Individuals in the following categories are more likely to develop complications:10
- Elderly individuals aged 65 or above
- People with chronic diseases, such as diabetes, heart disease, asthma
- BMI of 40 or higher
- Pregnant women
- Children under 5 years old
For example, during the 2023/24 winter flu season, Hong Kong reported 6 child mortality cases. Among them, a 3-year-old boy who passed away in July 2024 was co-infected with Influenza A H1 virus and COVID-19, and died due to encephalopathy complications.
According to a paper in the Journal of the American Medical Association, the mortality rate for hospitalized flu patients can range from 3.7% to 3.8%. 11 Data from the World Health Organization (WHO) estimates that annually, approximately 290,000 to 650,000 people die from respiratory diseases related to flu infections.7
If you unfortunately contract Influenza A, you should try to rest at home and drink plenty of fluids to relieve symptoms. For fever or pain, you can take ibuprofen or acetaminophen under the advice of a doctor.
Doctors will also consider the patient’s condition and health needs (including the risk of side effects) before deciding whether to prescribe antiviral medications to alleviate symptoms and shorten the duration of illness. Currently, commonly prescribed antiviral drugs in Hong Kong include:
- Relenza (Zanamivir)
- Tamiflu (Oseltamivir)
- Xofluza (Baloxavir marboxil)
Although antiviral medications can speed up patient recovery, patients should still follow their doctor’s instructions and not stop taking medication on their own or take it without a prescription, to avoid drug resistance or side effects.12
How Long Does it Take to Recover from Influenza A?
If you have Influenza A, you will usually recover on your own within 2–7 days. Coughs may last longer, while fever and other symptoms usually subside within 5–7 days.13 If symptoms persist for more than a week without improvement, you should seek medical attention promptly.
To differentiate between Influenza A and COVID-19, doctors use a “3-in-1 rapid test” (also known as ABC rapid test). This involves using a swab to collect a nasal sample from the patient to test for Influenza A, Influenza B, or COVID-19 infection.
In addition, you can also test yourself at home. Many healthcare brands have launched at-home flu rapid test kits that can simultaneously test for Influenza A, Influenza B, and COVID-19. Most provide results within 15 minutes and claim an accuracy rate of up to 99%.
Here are some brands and their prices for at-home rapid test kits:
| Brand | Price per Box |
| INDICAID™妥析™ COVID-19/Influenza A&B Rapid Antigen Test Kit | $40 HKD |
| 便利妥 COVID-19 & Flu Virus Antigen Rapid Test Kit | $40 HKD |
| SAVEWO 6-in-1 Antigen Rapid Test Kit | $29 HKD |
According to the recommendations of the Centre for Health Protection, you can prevent Influenza A in the following three ways:13
Get Seasonal Flu Vaccination
Seasonal flu vaccination is a safe and effective way to prevent seasonal influenza and its complications. Because flu viruses mutate from time to time and develop new strains, leading to widespread flu transmission, the WHO recommends the influenza vaccine composition to be used each flu season.14
Maintain Good Personal Hygiene
- Keep hands clean: Wash hands properly with liquid soap and water.
- Wear a mask: If you have respiratory infection symptoms and visit or work in high-risk places (such as elderly care homes, clinical areas of healthcare facilities), or are a high-risk individual for Influenza A, you should wear a mask.
- Proper mask use: Wear a mask correctly and maintain hand hygiene before and after wearing and removing it.
- Frequent hand washing: Wash hands frequently with liquid soap and water.
- Cover mouth and nose when sneezing or coughing: Use a tissue to cover your mouth and nose when sneezing or coughing.
- Stay home and seek medical advice if you have respiratory infection symptoms.
In addition, everyone should also maintain a balanced diet, regular exercise, sufficient rest, avoid smoking, and avoid excessive life stress.
Maintain Good Environmental Hygiene
- Regularly clean and disinfect frequently touched surfaces, such as furniture, toys, and shared objects.
- Use absorbent disposable paper towels to clean visible contaminants, such as respiratory secretions.
- Maintain indoor air circulation.
- Avoid going to crowded or poorly ventilated public places during the flu peak season.
The Department of Health also recommends the following flu prevention methods:
- Keep hands clean: Wash hands properly with liquid soap and water.
- Maintain cough etiquette: Cover your mouth and nose when sneezing or coughing.
- Wear a mask if you have respiratory infection symptoms.
- Maintain environmental hygiene.
- Maintain indoor air circulation.
- Avoid going to crowded and poorly ventilated public places during the flu peak season.
In addition, everyone should also maintain a balanced diet, regular exercise, sufficient rest, avoid smoking, and avoid excessive life stress.
Source
- 1Centers for Disease Control and Prevention. “Types of Influenza Viruses.” Centers for Disease Control and Prevention, CDC, 2 Nov. 2021
- 2衞生署 衞生防護中心. “季節性流行性感冒.” Www.chp.gov.hk, 25 July 2024
- 3香港特別行政區政府新聞公報. “香港已進入流感季節 衞生署呼籲市民立即接種疫苗.” Info.gov.hk, 9 Jan. 2025
- 4Johnson , Shannon . “Influenza a vs. B: Differences, Symptoms, Treatment, and More.” Www.medicalnewstoday.com, 24 Jan. 2024
- 5 Cowling, Benjamin J., et al. “Modes of Transmission of Influenza B Virus in Households.” PLoS ONE, vol. 9, no. 9, 30 Sept. 2014
- 6Anthony, Kiara. “Influenza B Symptoms.” Healthline, Healthline Media, 26 Mar. 2018,
- 7World Health Organization. “Influenza (Seasonal).” Who.int, World Health Organization: WHO, 3 Oct. 2023
- 8Nyirenda, Mayumbo, et al. “Estimating the Lineage Dynamics of Human Influenza B Viruses.” PLoS ONE, vol. 11, no. 11, 9 Nov. 2016
- 9Anthony, Kiara. “Signs and Symptoms of Type a Influenza.” Healthline, Healthline Media, 21 Dec. 2018
- 10CDC. “Key Facts about Influenza (Flu).” Centers for Disease Control and Prevention, CDC, 13 Sept. 2019
- 11U.S. pharmacist. “COVID-19 Mortality Rates versus Influenza during 2022-2023 Season.” Www.uspharmacist.com, 18 Apr. 2023
- 12衞生署 衞生防護中心. “新型甲型流行性感冒 - 禽流感.” Chp.gov.hk, 2024
- 13衞生署 衞生防護中心. “季節性流行性感冒.” Www.chp.gov.hk, 22 Dec. 2023
- 14衛生署 藥物辦公室. “季節性流感疫苗接種.” 衛生署 藥物辦公室
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The Bowtie Life Insurance Company Limited is an authorized life insurance company and Hong Kong’s very first virtual insurer approved. Through the use of modern technology and medical expertise, Bowtie offers an agent-free, commission-free and more convenient online platform for customers to quote, apply and claim for Voluntary Health Insurance Scheme (VHIS) anytime anywhere. Bowtie is ranked first in the direct channel sales throughout 2021.
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www.bowtie.com.hk The above content is provided by the Bowtie Team team. The information is for reference only and cannot replace any personal advice given by qualified medical professionals.
