Quadrivalent Influenza Vaccine

Influenza (flu) is an acute respiratory illness caused by influenza virus. The virus spreads among people mainly through droplet transmission and it can also be transmitted through contact of contaminated excretion. In Hong Kong, influenza happens in 2 seasons – from January to March and from July to August(1).

Incubation period of influenza virus is usually around 1-4 days. Signs and symptoms of getting infected of this virus include fever, cough, sore throat, running nose, muscle ache, fatigue, headache, vomiting and diarrhea etc. Healthy people may heal spontaneously 2-7 days after being infected. However, for people at old ages or with impaired immunity, influenza virus can cause bronchitis and pneumonia, and even result in severe complications that may be fatal.

There are 3 types of influenza virus identified: influenza A, influenza B and influenza C. Influenza type A (H1N1) is the most common source of local seasonal infection(1). The virus becomes infectious since one day before the onset of illness to the 5th-7th days during incidence. The virus is strongly infectious and has a high antigenic-drifting ability, meanwhile it is highly survivable. Owing to these reasons, even if we have ever been infected with the influenza virus, we may not carry enough antibodies specific to the subtypes of virus in each infection.

Each year, World Health Organization (WHO) assesses and recommends the subtypes of influenza virus that may cause epidemic infection in northern and southern hemispheres. Pharmaceutical companies will then develop vaccines for targeted protection against those viruses.

Recommended 2016-2017 northern hemisphere influenza season(2) :

  • A/California
  • A/Hong Kong
  • B/Brisbane
  • B/Phuket

Recommended 2017 southern hemisphere influenza season(2) :

  • A/Michigan
  • A/Hong Kong
  • B/Brisbane
  • B/Phuket

Apart from getting vaccination, maintaining good air ventilation, good personal health condition, good personal and environmental hygiene are essential to be staying away from being infected.

Quadrivalent vaccines are now the most protective vaccines available to prevent from influenza infection. WHO especially suggests the following groups of people to have vaccination:

  • Pregnant women
  • Children from 6 months old to 5 years old
  • Elderly aged 65 and above
  • Chronic diseases patients
  • Medical staff and those who need to take care of the sick

Side effects of the vaccines are usually mild, including pain, redness and swelling of the injection site, fatigue, low-grade fever and headache. For severe discomfort, please seek for medical consultation as soon as possible.


  1. Centre for Health Protection, Department of Health, Hong Kong – http://www.chp.gov.hk/
  2. World Health Organization – http://www.who.int/influenza/vaccines/virus/recommendations/2016_17_north/en/