Since 2010, annual vaccination against influenza has been recommended by the Centers for Disease Control and Prevention (CDC) for all people 6 months and older. The CDC has been recommending flu vaccination for healthcare workers since the early 1980s, and some facilities and healthcare systems now mandate it for their employees. The flu vaccine is 62% effective at preventing infections by influenza A and B viruses.1 Vaccination is effective at any time during the flu season, which in the United States generally runs from fall into spring.
The most common form of vaccination offered for the 2013-2014 flu season is the trivalent form. It covers three strains of virus, two influenza A types and one influenza B type. All multidose vials and injectable forms of the flu vaccines contain informational inserts that list exactly which strains of virus are targeted by it. This is important to note since patients are well informed about the flu. The strains targeted by vaccination differ each season. Being able to refer to correct information usually puts the patient at ease and decreases the reluctance he or she may have about receiving the flu vaccine.
Also available during the 2013-2014 flu season is the quadrivalent vaccination, which covers four strains of virus, two influenza A and two influenza B. An intradermal option is injected into the dermis as opposed to the muscle, and it is approved for patients ages 18 through 64.
Another option for vaccination is FluMist, which is delivered intranasally. This is a live attenuated vaccination used in healthy people ages 2 to 49. And still another option is a standard trivalent vaccine grown in cell cultures (Flucelvax). It can be safely given to patients who have an egg allergy.
The CDC does not recommend one flu vaccine over another. The important thing is to get vaccinated every year.
'Drift' and 'Shift'
Influenza viruses can change in two ways. One is called antigenic drift. These are small changes in the virus that occur continually over time. Antigenic drift produces a new virus strain that may not be recognized by the body's immune system. This is the main reason why antibodies against the older strains stop recognizing the newer virus and reinfection occurs. This is one of the main reasons people can get the flu more than one time in a flu season. However, with vaccination, the symptoms are less severe and the risk of complications such as pneumonia is reduced.
The other type of change is called antigenic shift, which is an abrupt major change in the virus that has emerged from the animal population. It is so different from the same subtype in humans that most people do not have immunity to the new (novel) virus. One example of this antigenic shift occurred in spring 2009, when a new H1N1 virus with a new combination of genes emerged and quickly spread, causing a pandemic. When such a shift occurs, most people have little or no protection against the new virus. Although influenza viruses are changing via antigenic drift all the time, antigenic shift occurs only occasionally.1
How Vaccines Are Designed
The job of producing a new vaccine for the next flu season starts well before the current flu season ends. Due to changes in the influenza viruses that circulate, a new flu vaccine is necessary each year. Scientists from around the world work to reformulate the vaccine to a few specific flu strains but do not include all the flu strains active in the world during that season. It takes about 6 months for manufacturers to formulate and produce the millions of doses required to address seasonal epidemics; occasionally, a new or overlooked strain becomes prominent during that time.3
It takes about 2 weeks for vaccine effectiveness to be established, meaning that a patient could become ill if exposed before that point but after the vaccine was administered. Another possible reason for feeling sick is that the vaccines can cause the immune system to react as if the body were actually being infected. General infection symptoms may appear, but they are usually not as severe or long-lasting as influenza symptoms.3
Contrary to what many people believe, no one can contract the flu from the flu shot itself. The viruses used to create the flu shot are inactive, so they are incapable of causing infection. The most dangerous adverse effect is a severe allergic reaction to either the virus material itself or residues from the hen eggs used to grow the influenza.
The first flu vaccine to use cell-based rather than egg-based technologies, Flucelvax, was approved by the FDA in November 2012 for use in people 18 and older.2 The manufacturing process for Flucelvax is similar to the egg-based production method, but the virus strains included in the vaccine are grown in cells of mammalian origin.2
A flu vaccine that is manufactured using another new technology was approved in January 2013 for use in people ages 18 through 49. Flublok does not require the use of actual influenza viruses and eggs are not used at any point in the manufacturing process.2 Flublok is made by genetically modifying a virus that infects insect cells to produce the flu vaccine protein. This protein, as in other flu vaccines, then triggers the immune system of the person receiving the vaccine to make protective antibodies.2
Best Tool Available
It is important to remember that although vaccination may not be a perfect match for the season, it provides some protection against the flu by reducing the severity of symptomology. Some people are at greater risk for serious flu-related complications: children younger than 5, people 65 and older, pregnant women, and people who have chronic lung disease, heart disease, blood disorders, endocrine, kidney or any chronic disease, or a weakened immune system. As healthcare providers, we must strongly encourage vaccination in these high-risk populations.
Although imperfect, influenza vaccines remain the best tool available for preventing illness from influenza.1
1. Centers for Disease Control and Prevention. MMWR Weekly Report - Interim Adjusted Estimates of Seasonal Influenza Vaccine Effectiveness-United States. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6207a2.htm
2. U.S. Food and Drug Administration. The Evolution, and Revolution, of Influenza Vaccines. http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm336267.htm
3. Centers for Disease Control and Prevention. Selecting the viruses in the Seasonal Influenza (Flu) Vaccine. http://www.cdc.gov/flu/professionals/vaccination/virusqa.htm
Lucianna Martone is a recent graduate from the family nurse practitioner program at Carlow University in Pittsburgh.