Quadrivalent Influenza Vaccine

Seasonal influenza is a common respiratory tract infection caused by human seasonal influenza viruses. The influenza viruses could be transmitted through respiratory droplets, and could be latent for 1-4 days. At the onset of influenza, the infected individual will manifest symptoms including malaise, runny nose, headache, coughing, fever and sore throat and etc. In Hong Kong, seasonal influenza is usually prevalent in months like from January to March and from July to August. Quadrivalent influenza vaccine is eligible for individuals aged 6 months or above, and is advised to be taken for comprehensive protection against influenza.
Product Code: V-FQS
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Why influenza vaccine 2021/2022 is being necessary?

Under the circumstances of COVID-19 pandemic, the risks for complication and mortality will be significantly getting higher, if you have accidentally contracted COVID-19 and influenza at the same time. Meanwhile, the likelihood of contacting COVID-19 would also be risen due to influenza-related hospitalization. Taking COVID-19 vaccine and influenza vaccine are therefore prominent and highly suggested. Apart from preventing Influenza and its complications, taking vaccine could also reduce the chance of having suspected symptoms at respiratory system, which in other way could avoid unnecessary anxiety. Vaccine residues are updated annually with the accordance to the prevailing strains, and it is always recommended to get vaccinated against seasonal influenza every year. In general, immune system will start to react and produce antibodies by approximately 2 weeks. Hence, it is recommended to have the vaccine administered at least 2 weeks before the beginning of the flu season, whereas providing adequate protection against influenza.

What is the composition of the suggested influenza vaccine 2021/2022?

The quadrivalent influenza vaccine advised by the Centre for Health Protection for the 2021-22 season contain the following components:

  • an A/Victoria/2570/2019 (H1N1)pdm09-like virus
  • an A/Cambodia/e0826360/2020 (H3N2)-like virus
  • a B/ Washington/02/2019-like virus
  • a B/Phuket/3073/2013-like virus

Who should be receiving the influenza immunization?

Proven that influenza vaccines are effective and low-risks, and the fact that severe conditions can happen even to robust individuals, the stakeholders of the society who aged 6 months or above, except those with known contraindications, should receive influenza vaccination for personal protection.With reference to Centre for Health Protection, it is claimed that when the vaccine strains are matching the circulating influenza viruses, the efficacy of vaccine in individuals who are younger than 65 years of age could reach 90%.

Ten Most FAQs related to Influenza

  1. What is the mode of transmission for influenza? How long will the incubation period and infectious period be? What are the clinical features?

Influenza is acute illness caused by influenza viruses, and antibiotics could not cure influenza or escalate the recovery period. The viruses could lay dormant for 1 - 4 days, and then become contagious 1 day prior to and up till 5 - 7 days after the symptoms are developed. The period could be longer for any children or severely immunocompromised individuals. Viruses could be passed to any individuals by respiratory droplets during sneezing, coughing or speaking, and also through direct contact with the secretions. Symptoms may include cough, runny nose, sore throat, muscle pain, fatigue, headache and fever, and some may experience vomit and diarrhoea.

  1. Who should be in priority to take quadrivalent influenza vaccine?

Within 2021-22 seasons, the Centre for Health Protection lists out the following priority groups for the vaccination:

  • Any individuals aged 50 or above
  • Pregnant women
  • Children aged 6 months to 11 years
  • Persons with chronic medical problems*
  • Healthcare workers or residents of Residential Care Homes

*Chronic Medical Problems may refer to chronic cardiovascular, lung, metabolic, or kidney disease, obesity (BMI 30 or above), immunocompromising conditions (also include weakened immune system due to disease or treatment), chronic neurological condition, or lack of ability to care for themselves.

  1. How many doses should the children receive?

For children aged under 9 years should receive 2 doses of quadrivalent influenza vaccine if they did not take any influenza immunization before, and the interval in between 2 doses should be at least 4 weeks. In another case, if the children have received influenza immunization in prior years, then they should only take 1 dose. Whoever aged above 9 years could also receive 1 dose regardless of their influenza vaccination history.

  1. When would be the influenza season?

In Hong Kong, the season would usually start in January and last until March, then will resume from July to August. However, if the influenza vaccine is not administered before the begin of influenza season, it is still suggested to get vaccinated as soon as possible, in order to ensure sufficient protection.

  1. Is it imperative to undertake influenza immunization every year?

Positive. It is more likely for circulating seasonal influenza strains to change on occasion, and therefore the vaccine composition will need to be revised for offering adequate protection against influenza. Immunity for the vaccinated person would be diminishing from time to time, and the level of antibodies would decline and become too low to provide any protection to the individual.

  1. Can COVID-19 vaccine be taken at the same day with influenza vaccine?

The Centre for Health Protection suggested a minimum interval of 14 days in between the two vaccinations to be taken place.

  1. Can pneumococcal vaccine be taken at the same day with influenza vaccine?

Yes, but they should be administered with separate syringe and at a discrete injection site.

  1. Will the vaccination of influenza be possible to cause influenza?

Negative. Quadrivalent influenza vaccine is a kind of inactivated vaccine, in which the viruses contained are already killed viruses, thus it would not result in influenza.

  1. What is quadrivalent influenza vaccine? Will there be any adverse reactions or side effects for taking this vaccine?

As an inactivated vaccine, quadrivalent influenza vaccine is considered to be almost risk-free and well tolerated, apart from occasional redness, swelling and soreness at the injection site. In general, there will not be any more side effects, unless occasionally, some vaccine recipients may encounter muscle pain, tiredness or fever at the beginning 6 – 12 hours after vaccination. All the discomforts above will gradually fade out by 2 days.

  1. Is there any subsidy scheme for influenza immunization in Hong Kong for 2021 / 2022?

According to Vaccination Subsidy Scheme 2021/2022, there are two major eligible groups as follows:

  • Children, as Hong Kong residents, aged from 6 months to less than 12 years, or of age 12 years or above but studying at primary school in Hong Kong
  • Persons of age 50 years or above, as Hong Kong residents, and be age of 50 years or above this year

*Individuals of age 50 years or above may enjoy the free injection service under the subsidy scheme, but appointments must be made in advance.

To learn more, please click here to visit the website of Centre for Health Protection.