The egg-based quadrivalent influenza vaccine recommended by the Scientific Committee on Vaccine Preventable Diseases (SCVPD) for the 2020/21 season contains the following:
- an A/Guangdong-Maonan/SWL1536/2019 (H1N1)pdm09-like virus
- an A/Hong Kong/2671/2019 (H3N2)-like virus
- a B/Washington/02/2019-like virus
- a B/Phuket/3073/2013-like virus
If trivalent influenza vaccine is being used, the influenza B component shall contain a B/Washington/02/2019-like virus.
Persons aged 9 years or above are recommended to receive one dose of 2020-21 influenza vaccine. To ensure adequate immunity against seasonal influenza, children under 9 years old who have never received any seasonal influenza vaccine are recommended to be given 2 doses of seasonal influenza vaccine with a minimum interval of 4 weeks in the 2020-21 season. Children who have received at least one dose of seasonal influenza vaccine in the 2019-20 season or before are recommended to receive one dose in the 2020-21 season.
No. A full adult dose of influenza vaccine cannot substitute a second dose. To ensure adequate immunity against influenza, children under 9 years old who have never received any influenza vaccine are recommended to have 2 doses of influenza vaccine with a minimum interval of 4 weeks.
The doctors should refer to the package inserts of individual products for the recommended age range of recipients and dosage.
As it usually takes about two weeks after vaccination for antibodies to develop in the body and provide protection against seasonal influenza virus, eligible persons are advised to visit participating private medical doctors' clinics for vaccination as early as possible to protect from the possible winter influenza season.
Both inactivated influenza vaccine (IIV) and live attenuated influenza vaccine (LAIV) are recommended for use in Hong Kong by SCVPD. Depending on individual brand, IIV are recommended for use among people aged six months of age or older, including healthy people and those with chronic medical problems. LAIV, which is a quadrivalent SIV, can be used for people aged 2-49 years except those who are pregnant, immunocompromised or with other contraindications. When deciding which SIV to give, the package inserts for individual products should always be referred to for indications, precautions and contraindications.
The VSS will cover the types of seasonal influenza vaccines recommended by the Scientific Committee on Vaccine Preventable Diseases (SCVPD) that are registered and supplied for use in Hong Kong. For the 2020-21 season, all available SIV in Hong Kong are quadrivalent SIV.
People who have a history of severe allergic reaction to any vaccine component or a previous dose of any influenza vaccine are not suitable to have inactivated seasonal influenza vaccination. Individuals with mild egg allergy who are considering an influenza vaccination can be given inactivated influenza vaccines (IIVs) in primary care setting, such as health centres or clinics. Individuals with a history of anaphylaxis to egg should have seasonal influenza vaccine administered by healthcare professionals in appropriate medical facilities with capacity to recognise and manage severe allergic reactions. Influenza vaccine contains ovalbumin (an egg protein), but the vaccine manufacturing process involves repeated purification and the ovalbumin content is very low. Even people who are allergic to eggs are generally safe to receive vaccination. Those with bleeding disorders or on anticoagulants should consult their doctors for advice. If an individual suffers from fever on the day of vaccination, the vaccination should be deferred till recovery.
(Note: All doctors are advised to read carefully the product information of the vaccine they have procured, noting especially the contraindications, route of administration, suitable age group, dosage for children and expiry date.)
Inactivated influenza vaccine (IIVs) is very safe and usually well tolerated apart from occasional soreness, redness or swelling at the injection site. Some recipients may experience fever, muscle pain, and tiredness beginning 6 to 12 hours after vaccination and lasting up to two days. If fever or discomforts persist, please consult a doctor. Immediate severe allergic reactions like hives, swelling of the lips or tongue, and difficulties in breathing are rare and require emergency consultation.
Influenza vaccination may be rarely followed by serious adverse events such as Guillain-Barré syndrome (about 1 to 2 case per million vaccinees) and severe allergic reaction (anaphylaxis) (9 per 10 million doses distributed). However, influenza vaccination may not necessarily have causal relations with these adverse events. Studies have shown that the risk of Guillain-Barré Syndrome after influenza infection (17.20 per million) is much higher than after influenza vaccination (1.03 per million).
(The Lancet Infectious Diseases. 2013 Sep; 13(9): 769-76)
LAIV is a live vaccine and is generally contraindicated in the following conditions, taking reference from recommendations of the United States, United Kingdom and Canada:
- History of severe allergic reaction to any vaccine component or after previous dose of any influenza vaccine;
- Concomitant aspirin or salicylate-containing therapy in children and adolescents;
- Children 2 years through 4 years who have asthma or who have had a history of wheezing in the past 12 months**;
- Children and adults who are immunocompromised due to any cause;
- Close contacts and caregivers of severely immunosuppressed persons who require a protected environment;
- Pregnancy; and
- Receipt of influenza antiviral medication within previous 48 hours.
** The UK recommended the use of IIV instead of LAIV for children with increased wheezing and/or needed additional bronchodilator treatment in previous 72 hours. Also, specialist advice should be sought on giving LAIV for children who require regular oral steroid for maintenance of asthma control or who have previously required intensive care for asthmatic attack. Canada recommended that individuals with severe asthma (currently on oral or high-dose inhaled glucocorticosteroids or active wheezing) or those with medically attended wheezing in the 7 days prior to vaccination should not use LAIV.
Individuals with mild egg allergy who are considering an influenza vaccination can be given LAIV in primary care setting, such as health centres or clinics. Individuals with a history of anaphylaxis to egg should have seasonal influenza vaccine administered by healthcare professionals in appropriate medical facilities with capacity to recognise and manage severe allergic reactions. Influenza vaccine contains ovalbumin (an egg protein), but the vaccine manufacturing process involves repeated purification and the ovalbumin content is very low. Even people who are allergic to eggs are generally safe to receive vaccination.
Service providers should always refer to the package inserts of individual products for detailed information.
The most common adverse reactions following LAIV administration are nasal congestion or runny nose (in all ages), fever (in children) and sore throat (in adults). The safety in pregnant women has not been established. Children aged below five years with recurrent wheezing / persons of any age with asthma may be at increased risk of wheezing following administration.
The viruses in inactivated influenza vaccine are killed viruses, therefore cannot cause influenza. The viruses in live attenuated influenza vaccine (LAIV) are weakened and cannot cause influenza in immunocompetent individuals. However, LAIV is not recommended for close contacts and caregivers of severely immunosuppressed persons who require a protective environment because of the theoretical risk of transmission of the live attenuated vaccine viruses to the severely immunosuppressed persons and cause disease.
There are several reasons why someone may get influenza / influenza-like illness even after they have been vaccinated. Firstly, because the body takes about 2 weeks to develop antibodies after vaccination, If a person is infected with influenza virus shortly after vaccination, he or she may develop influenza before becoming immune. Secondly, infection of viruses other than influenza virus can also result in illness similar to influenza, so people may falsely think that they had influenza despite being vaccinated. Thirdly, small number of people experience side effects after receiving inactivated influenza vaccine, for example fever and myalgia, which may be confused with influenza virus infection. Lastly, SIVs is unable to provide complete protection against influenza, because vaccine effectiveness depends on factors including the similarity between the virus strains present in the vaccine and those circulating in the community, as well as the characteristics of recipients, for example, age. Even so, all members of the public except those with known contraindications should receive SIV annually because influenza vaccination is one of the effective means in reducing the risk of influenza and its complications together with reduction in influenza-associated hospitalisation and death.