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Seasonal Influenza, Avian Influenza and Influenza Pandemic

What are the differences between seasonal influenza, avian influenza and influenza pandemic?

Seasonal Influenza (flu) is a highly infectious disease of the respiratory tract caused by influenza viruses. In Hong Kong, the disease is more common in periods from January to March/April and from July to August. Three types of Influenza viruses are recognised, among which influenza A and B viruses are more common than influenza C virus to cause human infection. Symptoms include fever, headache, muscle pain, runny nose, cough, sore throat and fatigue. For healthy individuals, influenza is usually self-limiting with recovery in 2-7 days.

Avian Influenza is caused by the influenza A viruses affecting mainly birds and poultry, such as chickens or ducks. Although transmission of avian flu virus to human has been observed, human-to-human transmission is inefficient.

Influenza Pandemic occurs when there is a major change (antigenic shift) in the influenza virus resulting in efficient human-to-human transmission. As the population will have very little or no immunity to the novel strain of virus, the virus spreads rapidly and extensively that affects a large number of people, resulting in higher severity of illness and a higher death toll worldwide.

What is the difference between seasonal influenza and avian influenza?

Seasonal influenza spreads through droplets when infected people cough, sneeze or talk. The infection may also spread by direct contact with the secretions of infected persons. Avian influenza transmits through contact with infected birds and poultry (live or dead) or their droppings, or contact with contaminated environments such as wet markets, live poultry markets or farms. Apart from flu-like symptoms in the early stage, people infected with avian influenza may have eye infection (conjunctivitis) or gastrointestinal symptoms (e.g. nausea, vomiting and diarrhoea). Since there is little or no immunity against avian influenza viruses in humans, high fever and complications such as chest infection, respiratory failure, multi-organ failure and death are more likely to result.

Is there a real threat for influenza pandemic?

Influenza pandemic occurs roughly every 10-50 years and there were three pandemics during the last century. In April 2009, influenza A (H1N1) pdm09 virus from the United States emerged to cause illness in human and resulted in a pandemic. A pandemic can occur if the viruses acquired the capacity to spread easily from person to person, either through adaptation or acquisition of certain genes from human viruses. Since the timing of a future pandemic is unpredictable, everyone should be prepared and take preventive measures.

How could we prevent seasonal influenza and avian influenza?

To prevent seasonal influenza:

  • Build up good body immunity with a healthy lifestyle including a balanced diet, regular exercise, adequate sleep and rest, relieving stress, do not smoke and avoid alcohol consumption
  • Wash hands often with liquid soap and water, and rub for at least 20 seconds, especially before touching eyes, mouth and nose; after going to the toilet; before handling food or eating; when hands are contaminated by respiratory secretion and after touching public installations
  • Cover your mouth and nose with tissue paper when sneezing or coughing. Dispose of soiled tissues into a lidded rubbish bin, then wash hands thoroughly
  • Ensure good indoor ventilation and environmental hygiene including cleaning the dustproof net of air conditioner regularly
  • Wear a surgical mask, avoid going to work or school as well as crowded places if symptoms of respiratory infections occur
  • Avoid going to crowded public or poorly ventilated places during peak seasons of influenza
  • Receive seasonal influenza vaccination to provide a safe and effective way of preventing influenza and its complications

to prevent avian influenza:

  • Avoid touching poultry or their droppings and do not blow at their bottoms
  • Wash hands thoroughly with liquid soap and water immediately after contact with poultry, birds and their droppings
  • Avoid visiting wet markets, live poultry markets and farms when travelling to affected areas
  • Cook poultry and eggs thoroughly before eating

When the following happens, what should we do?

If you have flu-like symptoms, you should

  • Wear a surgical mask and consult your doctor promptly if you develop symptoms such as fever, headache, muscle pain, runny nose, cough and sore throat
  • Tell your doctor your travel history if you have been to places with outbreak of avian influenza reported or had contact with poultry or their droppings
  • Maintain good personal hygiene and clean hands often with liquid soap and water. When hands are not visibly soiled, they could be cleaned with 70-80% alcohol-based handrub
  • Maintain good indoor ventilation

When the influenza pandemic comes, you should

  • Step up hygienic practices like washing hands and keeping the environment clean, and maintain good ventilation
  • Avoid going to crowded or poorly-ventilated places
  • Wear a surgical mask if you develop respiratory symptoms and seek medical advice early. You should also wear a surgical mask when caring for the sick, and when visiting hospitals or clinics
  • Watch out for the latest situation of the influenza pandemic and further announcements from the government
  • Pay attention to and comply with guidelines issued by the government with respect to travelling, port health control and suspension of public events as needs arise

Are the following preventive measures effective?

Can "flu shots" prevent avian flu?

Receipt of an influenza vaccine cannot prevent human infection with avian influenza. However, the vaccine provides a safe and effective way for preventing seasonal influenza and its complications, reducing the chances of hospitalization. Except those with known contraindications, individuals aged 6 months or above are recommended to receive the influenza vaccine to protect their health, especially the elderly who are having a higher risk of infection and complications.

Should I self medicate Oseltamivir (Tamiflu) to prevent infection?

Oseltamivir (neuraminidase inhibitor) is a type of prescription-only oral antiviral drug which reduces the replication of influenza A and B viruses. Self-medication is not advised because of the potential side effects and contraindications. Moreover, inappropriate use may give rise to antiviral resistance.

8 Steps to Protect Yourself
Step 1 Be prepared at home Step 2 Get vaccinated
Step 3 Keep hands clean Step 4 Maintain cough manners
Step 5 Use surgical masks properly Step 6 Live a healthy lifestyle
Step 7 Maintain good environmental hygiene Step 8 Prevent avian influenza

For details, please visit the Centre for Health Protection Website at

Elderly Health Service
Department of Health
November 2019

Related information

Vaccination for Seasonal Influenza