Influenza Vaccination

Haya Ahram, MD

Alumna - Weill Cornell Medicine-Qatar

The annual epidemic influenza illness is caused by influenza viruses type A and B. Isolated from humans as early as the 1930s, these viruses produce a contagious respiratory infection that can range from mild to severe illness, and in some cases can lead to death. Influenza season spans autumn and winter, with peak activity occurring December through February in the Northern Hemisphere and June through August in the Southern Hemisphere. The first inactivated influenza vaccine was produced in the early 1940s at the University of Michigan using fertilized chicken eggs, a method still in use for vaccine production today. Vaccination against the influenza viruses remains the most effective method for prevention of infection and reduction of serious outcomes, including hospitalization and Intensive Care Unit stays. Influenza viruses are constantly undergoing genetic change that impacts subsequent vaccine compositions and their induced immunity. The vaccine composition is reviewed and updated biannually based on what is predicted to be the most prevalent viral strain of the season, the extent to which it is spreading and the effectiveness of the previous season’s vaccine. The above information is discussed via a consultation between the World Health Organization (WHO) and six international collaborating centers to recommend viral strains for vaccine inclusion. Ultimately, the final decision regarding vaccine composition is made by each country individually. The Food and Drug Administration (FDA) makes the final decision about vaccination composition for the United States.

Currently, routine annual vaccination is recommended for all persons greater than or equal to 6 months of age without contraindications. For the current 2021-2022 season, all vaccines are quadrivalent (protect against four influenza viruses) and can be delivered via injection (Inactivated Influenza Vaccine 4 [IIV4] and Recombinant Influenza Vaccine 4 [RIV4]) or nasal spray (Live Attenuated Influenza Vaccine 4 [LAIV4]). LAIV4 should not be administered to pregnant women, those with chronic medical conditions or those who are immunocompromised. Persons who are in isolation due to COVID-19 infection or in quarantine due to suspected/known exposure should defer influenza vaccination until they have made a full recovery or have concluded their quarantine, in order to prevent potential exposure to those in the vaccination setting. Additionally, moderate to severe COVID-19 illness or other illnesses with or without high-grade fevers are a precaution to vaccination. Influenza vaccination may be administered concurrently with COVID-19 vaccination at different injection sites. Vaccination against both influenza A and B and COVID-19 should be offered and encouraged to all who are candidates in order to help limit the spread of infection, lessen illness severity and protect vulnerable populations.

For more information, please refer to:

- Influenza (Flu). (2021). Center for Disease Control. https://www.cdc.gov/flu/index.htm

- Influenza Vaccine for the 2021–2022 Season. (2021). Food and Drug Administration. https://www.fda.gov/vaccines-blood-biologics/lot-release/influenza-vaccine-2021-2022-season

- Global Influenza Programme. (2021). World Health Organization. https://www.who.int/teams/global-influenza-programme/vaccines