We have all heard people say it before: “I don’t believe in the flu shot.” Whether it is because they think they are too healthy to require one, only get sick when they get the shot, or believe that the flu shot does not work in general, many well-educated, logical folks become rather emotional when it comes to the subject of influenza vaccines. Even some individuals who accept every other vaccination waffle when it comes to the seasonal influenza vaccine. This uncertainty is not completely unfounded. Unlike most other vaccines that are essentially static in their composition from year to year, the influenza vaccine is a unique combination of influenza strains that changefrom year to year.
This is a necessity, as, unlike many other disease-causing organisms, the influenza virus is a highly evolved, rapidly mutating pathogen. Scientists have to make an educated guess on what strains will prevail several months in advance of use. Getting the influenza shot right is like hitting a moving target, only the stakes are much higher.
More than 100 countries with surveillance centers collect influenza samples throughout the year, sending them to laboratories run by the World Health Organization (WHO). This year’s 2015-2016 influenza vaccine for the northern hemisphere was announced on February 26, 20151 with the trivalent vaccine containing two strains of influenza A and one strain of influenza B and the quadrivalent vaccine containing an additional B virus2.
The vaccine is most effective when circulating strains of influenza in the population “match” the strains that were chosen to be in the vaccine. During seasons when vaccine viruses and circulating influenza viruses are well matched, a vaccine effectiveness (VE) between 50% and 60% has been observed1.
For the 2014-2015 influenza vaccine, the overall VE estimate was 19%. This means that last year’s influenza vaccine was only 19% effective at reducing a person’s need to seek medical care for an influenza-related illness. This “miss” was attributed to a predominant strain of H3N2 virus that was mutated and that did not appear until after the vaccine composition had already been chosen and manufactured.
As providers, talking patients into a vaccine that was only 19% effective last year is a tough sell. As it remains, however, annual vaccination is the best option we have for preventing influenza and influenza-related illness. Everyone aged 6 months and older should get the influenza vaccine every season, as recommended by the CDC since 20103.
An average of 36,000 deaths and more than 200,000 hospitalizations associated with influenza occur each year in the United States4. While most healthy individuals will develop only mild illness from influenza, vaccination in healthy working adults can reduce rates of influenza-like illness, lost workdays, and physician visits. Vaccination is even more important for vulnerable populations such as children, adults aged 65 years and older, pregnant women, residents of nursing homes, and people with asthma, heart disease, and diabetes.
So what is the take-home message? Vaccinate everyone aged 6 months and older annually. Even if the influenza shot “misses” as it did last year, it remains one of the best tools we have to help our patients live healthier lives.
Lori Sanders, BSN, FNP, works in the intensive care unit at Jefferson Hospital in Pittsburgh, Pa.
- CDC presents updated estimates of flu vaccine effectiveness for the 2014-2015 season. Atlanta, GA: Centers for Disease Control and Prevention. http://www.cdc.gov/flu/news/updated-vaccine-effectiveness-2014-15.htm. Published February 2015.
- Recommended composition of influenza virus vaccines for use in the 2015-2016 northern hemisphere influenza season. Geneva, Switzerland: World Health Organization. http://www.who.int/influenza/vaccines/virus/recommendations/2015_16_north/en/. Published February 26, 2015.
- CDC’s advisory committee on immunization practices (ACIP) recommends universal annual influenza vaccination [news release]. Atlanta, GA: Centers for Disease Control and Prevention. http://www.cdc.gov/media/pressrel/2010/r100224.htm. Published February 24, 2010.
- Bridges CB, Thompson WW, Meltzer MI, et al. Effectiveness and cost-benefit of influenza vaccination of healthy working adults. JAMA. 2000;285:1655-1663. doi: 10.1001/jama/284.13.1655