- Influenza B viruses,
- Influenza virus type A (H1N1)viruses,
- Influenza A (H3N2) viruses.
Types of Flu Shots
There are different types of flu vaccines. They are categorized according to
- The route of administration
- Their potency
- The ingredients
There is another method that further classifies these vaccines.
- Trivalent flu vaccines are those that are effective against three types of flu viruses.
- Quadrivalent flu vaccines are effective against four strains of the influenza viruses.
1) The intramuscular flu vaccine
This flu shot vaccine which is usually or traditionally used, contains the dead flu viruses which stimulate the formation of the antibodies by the immune system. These viruses are dead and hence without any virulence and therefore the flu shot cannot give you flu. These shots are indicated in all people above the age of 6 months till the age of 64 years including healthy people, people with chronic illnesses (such as asthma, diabetes and chronic lung diseases), pregnant women and people with high risk careers such as health workers.
2) The high dose intramuscular flu shot
This type of flu vaccine contains a higher dose of the same vaccine and is recommended for adults over the age of 65 years. This is to compensate for a weakened immune system in the elderly.
3) The intradermal flu shot
This vaccine with contents similar to the traditional shot is administered into the skin. It has a very small needle which penetrates only skin deep. It is administered into the dermis to people in the age group of 18 to 64 years.
4) The nasal spray flu vaccine
This vaccine is also called the FluMist or LAIV (Live Attenuated Influenza Virus) does not contain dead flu viruses but live weakened viruses and is recommended for people between the ages of 2 years to 49 years. Pregnancy, people above the age of 50 years and those with a chronic medical condition are contraindications to this vaccine. Though the flu virus is live, this vaccine too cannot cause flu because the virus is weakened and has a very low virulence, enough to be tackled by the immune system. The advantage of the nasal spray flu vaccine is that it is sprayed into the nostrils by a needle-less syringe and does require to be injected and therefore avoids the pain of the injection. This makes it the vaccine of choice in children and people who would rather not be injected. This vaccine produces antibodies in the blood as well as in the nose, which is normally the flu virus’s point of entry into the body. The other flu vaccines produce antibodies in the blood only.