Pharmacist Lin Sheng-Ju from the Clinical Pharmacy Department.
Seasonal influenza is an acute respiratory illness caused by the influenza virus, which can be classified into four types: A, B, C, and D. Type A or Type B influenza viruses can cause widespread outbreaks. Type A influenza viruses can infect both humans and animals, while Type B has so far been found only in humans.Symptoms include fever, headache, muscle aches, and cough, and some infected individuals may experience complications such as pneumonia, encephalitis, or myocarditis. Most patients recover on their own after infection.
The influenza vaccines currently in use are based on the antigen composition recommended annually by the World Health Organization for the Northern Hemisphere. The vaccines consist of inactivated vaccines and live attenuated vaccines. The trivalent influenza vaccine contains three strains of inactivated viruses: two type A strains (H1N1 and H3N2) and one type B strain, while the quadrivalent vaccine includes an additional type B strain.
In terms of vaccine production methods, there are egg-based vaccines, cell culture vaccines, and recombinant vaccines. All licensed influenza vaccines in our country are inactivated, meaning that they cannot cause influenza when administered.
According to recommendations from the Advisory Committee on Immunization Practices (ACIP) of the Ministry of Health and Welfare in our country, influenza vaccination is advised before each flu season for high-risk groups. These include children aged 6 months to under 5 years, adults aged 65 and older, individuals with underlying conditions (such as high-risk chronic illnesses, BMI ≥ 30, rare diseases, and severe illnesses), pregnant women, residents of nursing homes or long-term care facilities, healthcare and public health workers, and individuals living with or caring for high-risk groups (such as parents of infants under 6 months old).
Generally, the protective effect of the influenza vaccine gradually decreases about six months after administration, so annual vaccination is required. It takes approximately two weeks after vaccination for immunity to develop. For children under nine years old receiving the vaccine for the first time, two doses are needed to achieve full protection.
Common side effects of the influenza vaccine include pain and swelling at the injection site. Some individuals may experience systemic reactions such as fever, headache, muscle aches, nausea, and skin itching, which generally resolve on their own within 1 to 2 days. The occurrence of severe side effects is very low.
For individuals experiencing fever or those suffering from acute moderate to severe illness, it is advisable to wait until their condition stabilizes before getting vaccinated. Those who have experienced Guillain-Barré Syndrome (GBS) within six weeks of prior vaccination should consult a physician for evaluation.
The influenza vaccine can be administered simultaneously with other live or inactivated vaccines, or at any interval from them.