Rationale
Influenza is a disease caused by a virus. The flu is unlike other illness in that antibiotics will not cure it. The treatment of influenza is mainly symptomatic, meaning that the medications given are only to reduce the symptoms caused by the illness, not to treat the cause of the illness. If you have a fever, then medicine to lower the temperature will be given; if you experience muscular and joint pain, then medicine to relieve the pain will be given. There are antiviral medications that can be given within the first 48 hours of exposure to the flu to reduce flu duration.

Generic and brand names
The generic name is Quadrivalent influenza vaccine (split virion, inactivated). The brand name is Fluarix Tetra.

Composition of the vaccine
This vaccine contains the antigens for the following types and subtypes of viruses:

• A/Michigan/45/2015 (H1N1)pdm09 – like strain (A/Singapore/GP1908/2015, IVR-180)
• A/Hong Kong/4801/2014 (H3N2) – like strain (A/Hong Kong/4801/2014, NYMC X-2638)
• B/Brisbane/60/2008 – like strain (B/Brisbane/60/2008, wild-type)
• B/Phuket/3073/2013 – like strain (B/Phuket/3073/2013, wild-type)

Each 0.5 ml vaccine dose contains 15 ug haemagglutinin of each of the recommended strains.

Mechanism of action
This vaccine provides active immunization against four influenza virus strains (two A subtypes and two B types) contained in the vaccine and induces humoral antibodies against the haemagglutinins. These antibodies neutralize influenza viruses.

Schedule of administration
The flu vaccine is given once a year during flu season which starts in October.

Indications and usage
This vaccination is administered to persons aged 3 years and over. If the recipient is between 3 to 9 years and if there was no history of previous vaccination with influenza, he/she needs to be revaccinated at least four weeks later.

Precautions

• Always review the clinical history of the patient especially the previous vaccinations and occurrences of undesirable events;
• Appropriate medical treatment and supervision should always be readily available in case of anaphylactic event following the administration of the vaccine;
• Vaccination should be postponed if the patient suffers from acute severe febrile illness;
• The vaccine should never be administered intravenously;
• This vaccine should be injected intramuscularly with extreme caution to individuals with thrombocytopenia or any coagulation disorder since bleeding may occur following an intramuscular injection;
• This vaccine should be used in pregnancy only when clearly needed, and the possible advantages outweigh the potential risks for the fetus.

Side effects
The very common side effects of this vaccination are irritability, myalgia, pain at the injection site, and fatigue. Common side effects are the loss of appetite, drowsiness, headache, gastrointestinal symptoms (including nausea, vomiting, diarrhea, and/or abdominal pain), arthralgia, redness at the injection site, swelling at the injection site, shivering, and fever. The very uncommon side effects are dizziness, rash, hematoma and pruritus at the injection site.

Dosage and mode of administration
This vaccine is administered by intramuscular injection at the deltoid muscle (shoulder muscle) or at the anterolateral thigh, depending on which area has the greater mass. It means that it could be injected into your muscle.

To prevent the occurrence of anaphylactic (allergic) reaction, which could be fatal, this vaccine is not given via the intravenous route—that is, it is not given directly to your blood vessel. It is not also given under your skin. A single 0.5 ml dose of the vaccine is injected to you whenever you are scheduled to receive it.