Influenza is an acute respiratory infection caused by influenza virus. Influenza viruses are classified into types A, B and C. The main seasonal influenza viruses are types A and B, while type C is characterized by mild upper respiratory tract infection. At present, H1N1 and H3N2 are the primary influenza A viruses that infect humans.

Compared with the common cold, the symptoms of influenza are usually more sudden and severe, and its recovery time is longer than the common cold, ranging from a week to a few weeks. Sometimes it can cause complications such as pneumonia, encephalitis, and pericarditis and even lead to death. Influenza virus also has an important characteristic, that is, it is very easy to mutate, and is quite infectious. When the antigens of the virus change, it will have the ability to hit most of the population, and different degrees of mutation will cause epidemics of varying scales in a short time.

Vaccination suggestions

The protective effect of influenza vaccines varies according to age or physical condition, with 70%-90% protection in healthy adults and 50%-60% reduction in hospitalization due to complications of influenza in the elderly, and 80% reduction in mortality.

In addition, the protective effect of the vaccine also depends on whether the current vaccine strains match the actual prevalent virus strains, and the general protective effect will decrease with the increase of the difference of virus types. After completion of influenza vaccination, it will take at least two weeks to produce protective effect. Four to six months following vaccination, the protective effect of the vaccine may decline. Generally, the protective effect does not exceed one year. Therefore, it is recommended that the vaccine should be administered once a year.

Current influenza vaccines are divided into trivalent and tetravalent vaccines. Every year, the government-sponsored influenza vaccine will be updated for the viral strain composition according to the World Health Organization's annual recommendation to the Northern Hemisphere. It contains three inactivated viruses, namely two A viruses (H1N1/H3N2) and one B viruses. In addition to those the vaccine targets at public expense, the general public can also consider vaccination at their own expense.

In response to the often inaccurate prediction of influenza B: Only 47% of the predictions of influenza B in Taiwan from 2000 to 2016 were correct. At present, there are self-paid tetravalent influenza vaccines covering two kinds of type A and type B (Victoria and Yamagata) on the market, providing another option for complete prevention of influenza. In tetravalent vaccines, if the prediction of influenza B is correct, more than 80% of the protection will be achieved, while only 30-40% for prediction error.

Who is not fit for influenza vaccination?

Those who have allergies to the components of vaccines, and those who have had serious adverse reactions in the past will not be vaccinated. Current research has found that vaccination of chicken-embryo influenza vaccines for those with egg allergies will not affect the incidence of allergic reactions. International recommendations suggest that those with egg allergies can safely receive influenza vaccines.

Is the flu vaccine safe? What are the possible side effects?

After vaccination, there may be pain and redness at the injection site, while a few people will have mild systemic reactions, such as fever, headache, muscle ache, nausea, skin itching, urticaria or rubella, which will go away naturally within 1 to 2 days after the occurrence.

Severe side effects, such as immediate anaphylaxis or even anaphylactic shock, are rare, and when they do occur, symptoms usually begin within minutes to hours of vaccination. It is suggested that in order to be able to have medical treatment immediately after any accident, recipients take a rest at or near the inoculation unit after vaccination and be placed under observation for at least 30 minutes, and they can leave if no discomfort is detected.

Reminders

• Although vaccination can effectively reduce the chance of infection with influenza virus, you may still suffer from respiratory infection caused by other non-influenza viruses. Please pay attention to personal health care and various preventive measures to maintain your health.
• The World Health Organization (WHO) recommends that tetravalent influenza vaccines have broader protection against influenza B than trivalent vaccines. Although government-funded influenza vaccines are currently limited to trivalent vaccines, our hospital offers self-paid tetravalent vaccines for the public to choose from. For any questions, please consult the family medicine department.