Preventing Influenza

Prevention

The most effective way to prevent influenza is to get the influenza vaccine in advance. In special situations, influenza can also be prevented by taking antiviral medications. Classic preventive measures such as handwashing and cough etiquette should always be followed in daily life.

Vaccination

1. Components and method of influenza vaccination Most influenza vaccines used in Korea are inactivated split vaccines and contain antigens from new virus strains that are expected to circulate in winter. The WHO announces around the end of February each year three vaccine strains in total, one each for A(H3N2), A(H1N1), and B, which are expected to circulate in the coming winter. Based on this, vaccine companies produce trivalent influenza vaccines. Influenza vaccination should be received at least one month before the outbreak season to be effective, so vaccination for high-risk groups should be carried out in October and November.

2. Preventive effects of influenza vaccines Influenza vaccines do not completely prevent the onset of influenza, but they can reduce clinical symptoms and disease severity, and lower the risk of hospitalization and death. The preventive effect of influenza vaccines varies depending on whether the vaccine strain matches the circulating strain, as well as the recipient’s age and immune status.

3. Priority groups for influenza vaccination If older adults or patients with chronic medical conditions (such as heart disease, lung disease, diabetes, liver disease, kidney disease, cancer, or those taking immunosuppressants) get influenza, bacterial pneumonia may occur as a complication, or their existing chronic illness may worsen, increasing the risk of hospitalization or death. In addition, influenza worsens chronic diseases and can lead to death.

Infants and young children between 6 and 23 months of age, as well as pregnant women, also experience increased hospital admission rates due to respiratory complications when they get influenza. Therefore, those at high risk of hospitalization or death from complications when they catch influenza, that is, the "high-risk group," are priority candidates for active influenza vaccination. In addition, even people who are healthy themselves but have frequent contact with high-risk groups and may transmit influenza to them are also candidates for vaccination. These include healthcare workers, nursing home staff, household members of high-risk individuals, and people who come into contact with patients with high-risk conditions (home visitors, nurses, volunteers, caregivers), among others.

4. Side effects, contraindications, and precautions of influenza vaccines Influenza vaccines have been used for more than 60 years and are safe vaccines that are administered to 300 million people worldwide every year. After influenza vaccination, local reactions such as pain, redness, and induration at the injection site are the most common side effects (10-20%). Local side effects are temporary and usually resolve spontaneously within 1-2 days. Nonspecific systemic reactions such as fever, chills, fatigue, and muscle pain may also occur. Such systemic reactions appear about 6-12 hours after vaccination and last for 1-2 days before disappearing. Very rarely, immediate hypersensitivity reactions (angioedema, allergic asthma, or systemic anaphylaxis) may occur, and these are thought to be caused by some vaccine components, especially egg protein.

Antiviral prevention

Antiviral medications are also used for the preventive treatment of influenza, but they should be used as an adjunct to vaccination. Neuraminidase inhibitors (Tamiflu, Relenza) have a 70-90% preventive effect against influenza. The preventive use of neuraminidase inhibitors has been proven effective in the event of influenza occurring within a family, influenza outbreaks in the community, and influenza outbreaks in nursing homes.

Neuraminidase inhibitors are an effective means of preventing influenza in people who have not been vaccinated, when the vaccine strain does not match the currently circulating virus strain, and in high-risk groups that require additional preventive measures. Neuraminidase inhibitors do not have any significant effect on antibody production after influenza vaccination. Therefore, if vaccination is given late during the influenza season, they can be used for prevention until antibodies have formed.

So far, I have explained the prevention of influenza. In the next installment, we will look at migraine.

Source: Korea Disease Control and Prevention Agency National Health Information Portal