Obtaining flu vaccine used to be simple. There was one choice of vaccine that protected against three different flu viruses. For the 2015-2016 flu season, there are now several flu vaccine options: trivalent, quadrivalent, standard-dose, high-dose, live-attenuated, inactivated, intra-dermal, nasal, etc.
Why did things get so complicated? More vaccine options for our patients may mean better protection. Many formulations provide options that may create a stronger immune response in the person receiving the vaccine or allow some people to receive vaccination benefits that weren’t available with the traditional vaccine.
Despite having so many vaccine options available for the 2015-2016 flu season, the CDC and its Advisory Committee on Immunization Practices (ACIP) recommendations remain simple. The most important thing is for all people 6 months and older to get vaccinated against influenza. Don’t delay in providing a flu vaccine if you cannot locate a particular vaccine formulation. Optimally, vaccination should occur before the onset of influenza activity in the community and health care providers should offer vaccination by October, if possible.
Vaccination should continue to be offered as long as influenza viruses are circulating. To avoid missed opportunities for vaccination, providers should offer vaccination to unvaccinated persons more than 6 months old during routine health care visits and hospitalizations when vaccine is available.1
Here is a brief overview of the many vaccine options available for the 2015-2016 flu season.
- Trivalent versus Quadrivalent flu vaccine: The trivalent flu vaccine protects against two influenza A viruses (an H1N1 and an H3N2) and one influenza B virus. The quadrivalent flu vaccine protects against two influenza A viruses and two influenza B viruses. For years, flu vaccines were designed to protect against three different flu viruses (trivalent). This design included an influenza A H1N1 virus, an influenza A H3N2 virus and one B virus. Experts had to choose one B virus, even though there are two very different lineages of B viruses that both circulate during most seasons. This decision meant the vaccine did not protect against the group of B viruses not included in the vaccine. Adding another B virus to the vaccine aims to give broader protection against circulating flu viruses. If the quadrivalent vaccine is unable to be obtained, the CDC recommends not delaying getting a flu vaccine. The important thing is to get vaccinated against influenza.
- Live attenuated (nasal spray flu vaccine) versus Inactivated Influenza Vaccine (flu shot): Several studies conducted before 2009 demonstrated superior efficacy of the live attenuated vaccine in children. However, data from subsequent observational studies of live attenuated and inactivated vaccine effectiveness indicated that live attenuated did not perform as well as expected based upon the observations in earlier randomized trials. In the absence of data demonstrating consistent greater relative effectiveness of the current quadrivalent formulation of live attenuated vaccine, preference for live attenuated versus inactivated vaccine is no longer recommended. ACIP will continue to review the effectiveness of influenza vaccines in future seasons and update these recommendations if warranted.
- Standard-Dose versus High-Dose: Human immune defenses become weaker with age, which places older people at greater risk of severe illness from influenza. Also, aging decreases the body's ability to have a good immune response after getting influenza vaccine. A higher dose of antigen in the vaccine is supposed to give older people a better immune response, and therefore, better protection against flu. Data from clinical trials comparing standard-dose to high-dose among persons aged 65 years or older indicate that a stronger immune response (i.e., higher antibody levels) occurs after vaccination with high-dose vaccine. Whether the improved immune response leads to greater protection has been the topic on ongoing research. Fluzone® High-Dose is approved for use in people 65 years of age and older. Again, the CDC and its Advisory Committee on Immunization Practices have not expressed a preference for any flu vaccine indicated for people 65 and older.
- Recombinant influenza versus cell-culture based inactivated influenza vaccine: Recombinant influenza vaccine is produced differently and has a shorter shelf life than most influenza vaccines. Recombinant influenza vaccine does not use the influenza virus or chicken eggs in its manufacturing process. Cell-based flu vaccines are also developed through a different manufacturing process than the traditional egg-based manufacturing process that is used to develop flu vaccines. Cell-based flu vaccines are made by growing viruses in animal cells. Recombinant influenza vaccine and cell-based flu vaccines are being developed as an alternative to the egg-based manufacturing process. A major advantage of these technologies includes the potential for a faster start-up of the vaccine manufacturing process in the event of a pandemic. These vaccine may also be suitable for vaccinating people with egg allergies because they are not made using eggs.
- Intramuscular versus transdermal: Traditional flu shots are given intramuscularly. The intradermal flu vaccine is a shot that is injected into the skin instead of the muscle. The intradermal shot uses a much smaller needle than the regular flu shot, and it requires less antigen to be as effective as the regular flu shot. It is approved for people 18 through 64 years of age.
- Lisa A. Grohskopf, Leslie Z. Sokolow, Sonja J. Olsen, Joseph S. Bresee, Karen R. Broder, Ruth A. Karron. Prevention and Control of Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices, United States, 2015–16 Influenza Season. MMWR Morb Mortal Wkly Rep 2015;64:818-825.
- Centers for Disease Control and Prevention. FAQ: Types of Influenza Vaccine. http://www.cdc.gov/flu/faq/flu-vaccine-types.htm. October 6, 2015.
Author: Danielle Sebastian, PharmD, BCPS