Seasonal Influenza

The CDC recommends that everyone 6 months and older get vaccinated this season. School nurses play a key role in getting the word out about flu vaccine. 


Seasonal influenza refers to the limited periodic outbreaks of respiratory illness that typically occur in the fall and winter in the United States. While most people have some immunity to the circulating strains of the virus, annual influenza vaccine is recommended. Annual vaccine is prepared in advance of the influenza season. It is designed to match the influenza viruses most likely to be circulating in the community. The vaccine typically includes three virus strains: two influenza A viruses, each with a unique subtype determined by the surface antigens hemagglutinin(H) and neuraminidase (N), and one influenza B virus. The following nomenclature is used to describe annual influenza vaccine: 1. virus type, 2. geographic site where it was first isolated, 3. strain number, 4. year of isolation, and 5. virus subtype.

Pandemic influenza refers to a worldwide outbreak of influenza among people when a new strain of the virus emerges that has the ability to infect humans and to spread from person to person. During the early phases of an influenza pandemic, people might not have any natural immunity to the new strain; so the disease spreads rapidly among the population. A vaccine to protect people against illness from a pandemic influenza virus may not be widely available until many months after an influenza pandemic begins. Pandemics have occurred throughout history. They vary in severity from something that seems simply like a bad flu season to an especially severe influenza pandemic that could lead to high levels of illness, death, social disruption and economic loss.

Variant (Swine Origin) influenza viruses do not normally infect humans. However, sporadic human infections with influenza viruses that normally circulate in swine and not people have occurred. When this happens, these viruses are called "variant viruses." They also can be denoted by adding the letter "v" to the end of the virus subtype designation. 

Resources and Links

Association of State and Terroritial Health Officials: Public Health Access to Student Health Data

Centers for Disease Control and Prevention: Guidance for School Administrators to Help Reduce the Spread of Seasonal Influenza in K-12 Schools

Centers for Disease Control and Prevention: Influenza

Families Fighting Flu

Henry the Hand -- non-pharmaceutical infection prevention strategies

Immunization Action Coalition

National Sanitation Foundations: Scrub Club -- handwashing awareness initiative

Page last updated March 2020.