Influenza Vaccine

Influenza Vaccine

Compiled by Assoc. Prof. Sunee Techasupakornkul, Ph.D.

Disease and Significance

Influenza, also known as the flu, is a well-known infectious disease, especially during the global outbreak that occurred in 2009. In Thailand, in the year 2009, there were reports of 120,000 cases of influenza with 231 deaths. The disease is most prevalent during the rainy season until the end of winter. The cause of influenza is the influenza virus, with three types known as A, B, and C. The Influenza A virus, which is the cause of the disease and the annual epidemic, is further classified into various subtypes according to the protein structure of the outer shell, such as H and N, designated as H1N1 or H3N2. The H5N1 subtype is the cause of avian influenza. The virus constantly mutates, resulting in different amino acid sequences in the virus separated from each patient each year, even though they may be of the same subtype, such as H1N1, which leads to drug resistance.

Transmission of Influenza

Influenza is easily transmitted by coughing, sneezing, or talking, and the most common route is through the hands, which touch contaminated items such as nasal secretions, saliva, food, eyes, and noses. These are all pathways for the influenza virus to enter the body. Patients should frequently wash their hands, cover their mouths and noses to reduce the spread of the virus during coughing and sneezing. Infection can occur more easily in crowded places, such as schools, factories, and buses.

Symptoms of Influenza

The general symptoms of influenza are fever, chills, fatigue, cough, headache, muscle aches, and sometimes nasal congestion or sore throat. In children, there may be diarrhea and high fever, which can lead to convulsions. Most patients recover within 7-10 days, but less than 10% may develop serious complications, the most important of which is pneumonia, which can be fatal. Groups of people at high risk for serious complications from influenza include:

• Elderly people aged 65 and over
• Children under 5 years of age
• Severely obese individuals (weighing over 100 kilograms)
• Pregnant women over 16 weeks
• Patients with chronic diseases such as lung disease, heart disease, kidney disease, diabetes, immunodeficiency, or those with swallowing and breathing problems, such as epilepsy, asthma, and emphysema, and brain disabilities are eligible for the influenza vaccine.
• Children (under 18 years old) who need to take continuous aspirin

The influenza vaccine consists of two strains of influenza A viruses, H3N2 and H1N1, and one strain of influenza B virus. The strains included in the vaccine are newly changed every year, based on predictions of which strains will spread in that year. This is evaluated by the World Health Organization, based on viruses identified from patients in different regions around the world in the past year.

There are two types of influenza vaccines, including the live attenuated vaccine and the inactivated vaccine, both of which are propagated in fertilized chicken eggs. However, currently only the inactivated vaccine is available for sale in Thailand. The live attenuated vaccine is still under research and development by the pharmaceutical industry.

1) The original inactivated vaccine was made up of whole inactivated virus particles, but it had high side effects, so it was discontinued. The current inactivated vaccine has two types.

1.1) Split vaccine is produced by breaking up the virus particles using a lipid layer that surrounds them. Only the protein parts of the virus envelope (H, N) and other viral proteins remain. The split vaccine is available for sale in Thailand under the brand names Fluarix®, Fluzone®, and Vaxigrip®.

1.2) Subunit vaccine contains only the purified protein parts (H, N) of the virus envelope. Some companies add adjuvants to enhance the immune response. Subunit vaccines available for sale in Thailand include Agrippal S1®, Fluad®, and Influvac®.

Inactivated vaccines are made into liquid form in doses of 0.5 mL or 0.25 mL (1 dose) in a prefilled syringe or packaged in 5 mL (10 doses) in a glass vial, depending on the company.

Inactivated influenza vaccines can be given to all ages from 6 months and older, including those at high risk for complications from influenza infection, as well as medical personnel and those who care for high-risk groups.

2) Live attenuated influenza vaccines are made from viruses that can cause disease along with attenuated viruses that grow well at 25 degrees Celsius. There is an exchange of genes, resulting in attenuated viruses with H and N proteins that are similar to those of disease-causing viruses. The vaccine is administered via a nasal spray containing 0.2 ml (1 dose) in a tube with a dose metering valve that delivers 0.1 ml per spray.

Those who can receive live attenuated influenza vaccines are people between the ages of 2 and 49 who are in good health and not pregnant, as well as those who care for high-risk groups, including those working in neonatal intensive care units and those caring for cancer and HIV patients.

Size and Management of Vaccines

Immunity that occurs naturally from infection or from receiving both types of vaccines lasts no more than 1 year, and the strains that cause outbreaks each year differ. Therefore, it is recommended to receive the vaccine every year, once a year before the epidemic season. For Thailand, it is recommended to receive the vaccine before the rainy season, from late April to early May. If a person has been infected with the flu for more than 1 year, they should receive the vaccine again in the following year.

Inactivated virus vaccines are administered by injection into the muscle, 0.5 ml for children under 3 years old, and only 0.25 ml for children under 3 years old.

People aged 65 and over should receive Fluad ®, which contains adjuvants that can stimulate the immune system to a sufficient level to prevent the disease. The inactivated virus vaccine is administered by spraying into both nostrils, 0.1 ml each.

Children under 8 years old who have never received any type of flu vaccine should receive two doses of the vaccine in the first year, at least 1 month apart. In the following year, they should receive only one dose.

Effectiveness of the Flu Vaccine

2-3 weeks after receiving the vaccine, immunity (antibodies) begins to develop, which is high enough to prevent the disease. This will be at its peak from 2-4 months after vaccination and can prevent the disease for 6-12 months after vaccination. The efficacy of the flu vaccine in healthy 5-6 year old children is approximately 87% for the nasal spray vaccine and 70-90% for the inactivated virus vaccine.

However, the virus that causes illness each year is different from the viruses used to make the vaccine, so the effectiveness of the vaccine may not be very high. People who have received the vaccine still have a chance of getting sick, but the symptoms will not be severe because the immunity from the vaccine can still provide some protection. A study on the efficacy of inactivated virus vaccine against the flu in Thai elderly people in urban areas in 2007 found that 8.9% of vaccinated people were infected, compared to 16.9% of those who were not vaccinated.

Side Effects

Both types of vaccines have minimal side effects. For those who receive the inactivated virus vaccine, common side effects (more than 10%) include pain, swelling, and redness at the injection site for about 1-2 days, fatigue, headache, and muscle aches. Children under 5 years of age may experience drowsiness and loss of appetite. Inactivated virus vaccines with adjuvants have more side effects than those without adjuvants.

Common side effects (more than 10%) for those who receive the live attenuated virus vaccine include nasal congestion and runny nose, which can occur at any age. High fever is found in the age group of 2-6 years old, while sore throat is found in adults.

Prohibitions

1. Influenza vaccines that are available in the market contain viruses grown in chicken eggs. Therefore, individuals who are allergic to eggs or have a history of severe allergic reactions to influenza vaccines should not receive the vaccine. Symptoms of severe allergic reactions include pale skin, rapid heartbeat, dizziness, wheezing, and difficulty breathing with a loud whistling sound.

2. Children under 2 years old, individuals aged 50 years and above, pregnant women, and those who are at high risk of developing complications when infected should not receive live attenuated influenza vaccines.

3. Healthcare workers who are in close contact with immunocompromised individuals, such as patients undergoing bone marrow transplant, should not receive live attenuated influenza vaccines.

4. Individuals who have a history of allergies and experience stuffy nose or difficulty breathing are recommended to receive inactivated influenza vaccines instead.

5. If you are currently ill, such as having a high fever, it is recommended to postpone getting vaccinated until you are fully recovered. However, if you have minor illnesses such as allergies, itchy skin, common cold or sore throat with a low-grade fever, it is safe to receive inactivated influenza vaccines.

References:

Tittipong, Y. (2009). Surveillance report of influenza disease. Retrieved from http://epid.moph.go.th/Annual/Total_Annual.html

Centers for Disease Control and Prevention. (2010). Prevention and control of seasonal influenza with vaccines: recommendations of the advisory committee on immunization practices (ACIP). MMWR, 59(RR-8), 1-68.

Flumist (Package insert). (2011). MedImmune. Gaithersburg, MD. Retrieved from http://www.fda.gov/downloads/BiologicsBloodVaccines/Vaccines/ApprovedProducts/UCM123743.pdf.

Fluzone (Package insert). (2011). Swiftwater, PA. Retrieved from http://www.fda.gov/downloads/BiologicsBloodVaccines/Vaccines/ApprovedProducts/UCM195479.pdf

Usa Panichprathompong. (2007). Influenza in Thai senior citizens. Thailand Human Influenza Research Meeting Summary. AFRIM Clinical Trial Center Zmujme.