Disease Influenza

Influenza Transmission and Seasonal Outbreaks

Influenza can spread throughout the year. In Thailand, infections are commonly reported during the rainy and cooler seasons, although outbreaks may occur at other times.

Because circulating influenza strains change and protection from vaccination decreases over time, seasonal influenza vaccination is generally recommended every year.

Who Can Receive the Influenza Vaccine?

Annual influenza vaccination is generally recommended for people aged six months and above who do not have a medical contraindication. The vaccine may be given to children, adults, older people, and people with chronic medical conditions.

Pregnant women can receive an inactivated influenza vaccine during any stage of pregnancy. Vaccination also helps provide antibodies that may protect the baby during the first months of life, when infants are still too young to receive the vaccine themselves. Breastfeeding is not a reason to avoid influenza vaccination.

Types of Influenza Vaccines

Influenza vaccine formulations are reviewed and updated regularly to match the viruses expected to circulate during each season.

Depending on the product, country, and vaccination programme, vaccines may be formulated to protect against three or four influenza strains.

Trivalent Influenza Vaccine

A trivalent vaccine protects against:

๐ Two influenza A viruses, usually A(H1N1) and A(H3N2)

๐ One influenza B virus from the B/Victoria lineage

For the 2026 Southern Hemisphere season, the World Health Organization recommends a trivalent formulation.

Quadrivalent Influenza Vaccine

A quadrivalent vaccine contains:

๐ Two influenza A strains

๐ Two influenza B strains

Although the World Health Organization has recommended transitioning towards trivalent vaccines because the B/Yamagata lineage is no longer considered necessary, quadrivalent influenza vaccines may still be available in countries where the transition is not yet complete. Quadrivalent vaccines continued to be offered by some Department of Disease Control services in Thailand in 2026.

Benefits of Influenza Vaccination

Influenza vaccination cannot prevent every infection, but it can help:

๐ Reduce the likelihood of developing influenza

๐ Reduce the severity of illness

๐ Lower the risk of influenza-related complications

๐ Reduce the likelihood of hospitalisation

๐ Reduce the risk of severe illness and death, particularly among vulnerable groups

The vaccine should be updated annually because influenza viruses change and immunity from previous vaccination gradually declines.

Who Should Prioritise Influenza Vaccination?

Although most people aged six months and above may receive the vaccine, vaccination is particularly important for those at increased risk of serious complications.

Priority groups include:

๐ Pregnant women

๐ Young children aged six months and above

๐ Adults aged 65 years and above

๐ People living with obesity

๐ People with neurological conditions or disabilities that limit their ability to care for themselves

๐ People with thalassaemia or weakened immune systems

๐ People living with symptomatic HIV infection

๐ Patients receiving chemotherapy or immunosuppressive treatment

๐ People with chronic obstructive pulmonary disease

๐ People with asthma

๐ People with heart disease

๐ People with cerebrovascular disease

๐ People with kidney failure

๐ People with diabetes

Thailand’s Department of Disease Control continues to promote annual influenza vaccination among recognised high-risk groups to reduce serious illness and deaths from complications.

Who Should Not Receive or Should Postpone the Vaccine?

Children Younger Than Six Months

Influenza vaccines are not licensed for infants younger than six months. Protection during this period may be supported through maternal vaccination during pregnancy and vaccination of close family members.

Previous Severe Allergic Reaction to an Influenza Vaccine

A person who has experienced a severe allergic reaction, such as anaphylaxis, after a previous influenza vaccine or to a known vaccine component should consult a doctor before receiving another dose.

The doctor may recommend a different vaccine formulation, administration in a medically supervised setting, or evaluation by an allergy specialist.

Moderate or Severe Acute Illness

People who are moderately or severely unwell, with or without a fever, may be advised to postpone vaccination until their condition improves.

A mild illness or low-grade fever does not always require vaccination to be delayed, but suitability should be assessed by a healthcare professional.

Influenza Vaccination and Egg Allergy

Egg allergy alone is no longer considered a reason to avoid influenza vaccination.

Current guidance indicates that people with egg allergies may receive any influenza vaccine that is otherwise appropriate for their age and health condition. Standard precautions for recognising and treating allergic reactions should be available wherever vaccines are administered.

How Often Should the Influenza Vaccine Be Given?

Most people should receive influenza vaccination once every year.

Some children younger than nine years old who have never previously received an influenza vaccine may require two doses during their first vaccination season, usually given at least four weeks apart. The exact schedule should follow the doctor’s advice and the instructions for the vaccine being used.

Summary

Influenza is a contagious respiratory infection that can occur throughout the year and may cause serious complications in young children, older adults, pregnant women, and people with chronic diseases or weakened immune systems.

 

Reference:

Bangphai Hospital Influenza

ArokaGO Providers Bangphai Hospital