【Seasonal Flu Q&A】5 Key Facts You Should Know About Flu


【流感Q&A】流感5大注意事項 即睇病徵&治療方法

Seasonal flu seems to have a less significant impact in Hong Kong since the COVID-19 pandemic, but can we ever be sure that it’s not coming back? Many say that COVID-19 is just like a flu, little do they realize that flu complications could also be very deadly. How well do you actually know about flu?

1. What is flu?

Influenza (Flu) is a contagious respiratory illness caused by influenza viruses. There are usually 2 flu seasons each year and cause a lot of severe infections and even deaths globally. Three main types of flu viruses that spread in people are types A, B and C, whereas A and B are responsible for seasonal flu epidemics each year.

2. Any differences between seasonal and pandemic flu?

Season flu is usually caused by “antigenic drift” in flu viruses (changes in viruses’ surface proteins while maintaining similar antigenic properties), which is a primary reason why the composition of flu vaccines is reviewed annually to keep up with evolving flu viruses.

Pandemic flu is caused by “antigenic shift” which is an abrupt, major change in a flu virus. Therefore, when shift happens most people have little or no immunity against the new virus, and hence spreading more quickly and causing a pandemic. Flu pandemics occur rarely – usually once in 10 to 50 years.

3. What are the key features of flu?


Common symptoms include fever, fatigue, cough, sore throat, headaches, runny or stuffy nose, shortness of breath, muscle or body aches, vomiting and diarrhea etc.


Immunocompromised people might develop complications including bacterial pneumonia, ear infections, sinus infections and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes

How Flu Spreads

Mainly by tiny droplets made when people with flu cough, sneeze, or talk

Flu Seasons in Hong Kong

  • January - April (Winter)
  • July - August (Summer)


1 to 4 days


  • One day before symptoms develop and up to 5 days after becoming sick
  • Young children and people with weakened immune systems might be able to infect others for a longer time

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4. What should I do after infection?

  • Take adequate rest and drink plenty of water
  • Seek medical advice promptly if symptoms become serious or persistent
  • Take antibiotics prescribed by doctors if it is complicated by bacterial infection
  • High-risk groups for flu complications incl. children, ages 50+ and chronically ill patients, should take antiviral medicines prescribed by doctors in the first 48 hours of flu-like symptoms

Important: Antibiotics are used for treating bacterial infection but not viral infection. Taking antibiotics cannot speed up recovery from flu

5. How can I prevent seasonal flu?

  • Maintain good personal hygiene
  • Get a flu vaccine every autumn to develop enough antibodies against flu viruses
  • When flu symptoms arise, use flu A&B rapid antigen test to obtain a quick diagnosis to protect your family and friends