13 Nov 2020

2020 CHP influenza

Dear Parents and Guardians,

This letter is to inform you that the Centre for Health Protection (CHP) has notified schools about increased numbers of institutional upper respiratory tract infection (URTI) outbreaks. In addition, as Hong Kong continues to face the challenge of COVID-19 pandemic, influenza viruses and the virus that causes COVID-19 may both spread in the coming winter influenza season. A person getting influenza and COVID-19 at the same time may be more seriously ill.  Here is more information about seasonal influenza:

Causative agent

Seasonal influenza is an acute illness of the respiratory tract caused by influenza viruses. It is usually more common in periods from January to March/April and from July to August in Hong Kong. Three types of seasonal influenza viruses are recognised to cause human infection, namely A, B and C. Influenza A viruses can further be subtyped on the basis of two surface antigens: haemagglutinin (H) and neuraminidase (N). Currently, there are two subtypes of seasonal influenza A viruses circulating in humans, namely influenza A (H1N1)pdm09 and influenza A (H3N2). 

Clinical features

For healthy individuals, seasonal influenza is usually self-limiting with recovery in two to seven days. Symptoms may include fever, cough, sore throat, runny nose, muscle pain, fatigue and headache; some may also have vomiting and diarrhoea. 

Cough is often severe and prolonged but fever and other symptoms generally resolve in five to seven days. However, influenza can be a serious illness for the weak and frail or elderly people, and may be complicated by bronchitis or chest infection.  It may even cause death.

Mode of transmission

Influenza viruses mainly spread through droplets when infected people cough, sneeze or talk. The infection may also spread by direct contact with the secretions of infected persons.

Incubation period

Usually around one to four days.

Infectious period

Infected persons may pass the viruses to other people one day before and up to five to seven days after they develop symptoms. The period may be even longer in young children or severely immunocompromised persons.


  • Have adequate rest and drink plenty of water.
  • Refrain from work or attending classes at school when having symptoms of influenza. Seek medical advice if symptoms persist or the patient deteriorates.
  • Antibiotics which target bacterial infection but not viral infection will not cure influenza or make recovery faster.
  • Antiviral agents may reduce severity and duration of illness but must be used under doctor’s prescription.


The following measures are advised by the Centre for Health Protection to prevent upper respiratory tract infection:

  1. Seasonal influenza vaccination
  • Influenza can cause serious illnesses in high-risk individuals and even healthy persons. Given that seasonal influenza vaccines are safe and effective, all persons aged 6 months or above (except those with known contraindications) are recommended to receive influenza vaccine for personal protection.
  • Usually, it is suggested that vaccination should be received in autumn every year. About two weeks after vaccination, the body will develop a sufficient level of antibodies to protect against influenza virus infection.
  • For details on seasonal influenza vaccination, please refer to Vaccination Schemes and Vaccination for Seasonal Influenza.
  1. Personal hygiene
  • Surgical masks can prevent transmission of respiratory viruses from ill persons. It is essential for persons who are symptomatic (even if there are mild symptoms) to wear a surgical mask
  • Wear a surgical mask when taking public transport or staying in crowded places. It is important to wear a mask properly, including performing hand hygiene before wearing and after removing a mask. For details about the proper use of masks, please browse the following webpage: https://www.chp.gov.hk/en/healthtopics/content/460/19731.html
  • Avoid touching one’s eyes, mouth and nose
  • Perform hand hygiene frequently, especially before and after touching the mouth, nose or eyes; after touching public installations such as handrails or door knobs; or when hands are contaminated by respiratory secretion after coughing or sneezing.
  • Wash hands with liquid soap and water, and rub for at least 20 seconds. Then rinse with water and dry with either a clean cotton towel or a paper towel. If hand washing facilities are not available, or when hands are not visibly soiled, hand hygiene with 70 to 80% alcohol-based handrub is an effective alternative. To perform hand hygiene properly, please browse the following webpage: https://www.chp.gov.hk/en/healthtopics/content/460/19728.html
  • Cover your mouth and nose with tissue paper when coughing or sneezing. Dispose of soiled tissues into a lidded rubbish bin, then wash hands thoroughly.
  • When having respiratory symptoms, wear a surgical mask, refrain from work or attending class at school, avoid going to crowded places and seek medical advice promptly.
  • Build up good body immunity by having a balanced diet, regular exercise, adequate rest, reducing stress, do not smoke and avoid alcohol consumption. 
  1. Maintain good environmental hygiene
  • Regularly clean and disinfect frequently touched surfaces such as furniture, toys and commonly shared items with 1:99 diluted household bleach (mixing 1 part of 5.25% bleach with 99 parts of water), leave for 15-30 minutes, and then rinse with water and keep dry. For metallic surfaces, disinfect with 70% alcohol.
  • Use absorbent disposable towels to wipe away obvious contaminants such as respiratory secretions, and then disinfect the surface and neighbouring areas with 1:49 diluted household bleach (mixing 1 part of 5.25% bleach with 49 parts of water), leave for 15-30 minutes and then rinse with water and keep dry. For metallic surfaces, disinfect with 70% alcohol.
  • Maintain good indoor ventilation. Avoid going to crowded or poorly ventilated public places; high-risk individuals may consider putting on surgical masks while in such places.

You are also recommended to watch the video clips produced by the CHP on personal and environmental hygiene, which are available under “Video Demonstration” section of “Infection Control Corner” at the CHP website (https://www.chp.gov.hk/en/resources/346/index.html). 

If your child has a fever (oral temperature higher than 37.5 C, or ear temperature or forehead temperature higher than 38 C) or respiratory illnesses (even very mild symptoms only) , please seek medical advice immediately and keep your child at home for 48 hours after the fever has subsided. 

The epidemic situation has shown signs of resurgence recently and the winter influenza season is approaching. Hence, we have to stay vigilant. Students are reminded to check body temperature every day and wear masks at all times, maintaining proper hand hygiene and appropriate social distances, avoiding crowd gathering and paying attention to personal and environmental hygiene. Please feel free to contact me with any questions or concerns. 

Best regards,


Sha Tin College Nurse