I got my flu vaccine this week, have you? Flu season in the United States lasts from October through mid-May.1 Now is the perfect time to get vaccinated against the flu.
There are 13 (!!!) different types of flu vaccines approved for use in the USA.2 Vaccines can differ by method of administration (intramuscular injection, intradermal delivery system, and nasal spray, as well as vials that hold single or multiple shots), dosage (regular or high-dose), and type of vaccine (inactivated virus, live virus, and recombinant; trivalent vs. quadrivalent). Here, I will give a run-down on the various options for getting vaccinated against influenza.
There are many different strains of influenza virus. Which virus strains are selected for inclusion in the seasonal flu vaccine is based on global monitoring. This year (2014-2015), all of the influenza vaccines are made to protect against the following three viruses:
1) A/California/7/2009 (H1N1)pdm09-like virus
2) A/Texas/50/2012 (H3N2)-like virus
3) B/Massachusetts/2/2012-like virus
Some of the flu vaccines protect against an additional B virus, B/Brisbane/60/2008-like virus.3 Vaccines that give protection against three viruses are called trivalent vaccines. Vaccines that give protection against four viruses are called quadrivalent vaccines.
The immunization method that most people are familiar with is the needle-in-the-arm aka intramuscular injection or “flu shot.” These types of shots contain either killed virus or just pieces of virus that your immune system can use to identify, hunt down, and destroy invading influenza. Common side effects from the flu shot include soreness at the site of injection and low-grade fever. You cannot get the flu from a flu shot.4 The immune systems of the elderly make them susceptible to disease yet often times not responsive to vaccination; for this reason, those over 65 years of age should receive the Fluzone High-Dose shot (made by Sanofi Pasteur), which is specially formulated to induce a better response in the elderly.5 Fluzone is only available as a trivalent vaccine.
One common myth that has been perpetuated across the internet regarding vaccines is that they contain harmful amounts of mercury.4 Even though all evidence to date says that vaccines containing the mercury-based preservative thimerosal are safe, multiple manufacturers offer single-dose, pre-filled syringes of flu vaccine that are thimerosal-free. In addition, pediatric and high-dose flu shots do not contain thimerosal. (Side note: some areas are currently experiencing a shortage of the pediatric quadrivalent vaccine, which should be rectified by the end of October; the children’s trivalent vaccine is readily available6) Thimerosal is still present in multi-dose vials of flu vaccine which are commonly administered at pharmacies and your doctor’s office, but in most places you can request a single-dose thimerosal free version if you so desire.
For those afraid of needles, there are now two needle-less methods of achieving immunization against influenza. First, Sanofi Pasteur offers the Fluzone Intradermal vaccine, which uses a “microneedle” (only 1.5mm long) that injects vaccine into the skin, not deep into the muscle like a traditional flu shot.7 The most common side effects of this vaccine are redness, swelling or a raised bump, itching, and pain at the site of the injection. It is approved for use for people 18-65 years old and is available only as a trivalent vaccine.
The second needle-less option for immunization is Flumist (made by Medimmune).8 This quadrivalent vaccine contains a live, attenuated (weakened) virus that is administered via a nasal spray. Although the virus in the vaccine is “live,” it does not function like the flu virus found in nature: it is sensitive to heat and therefore cannot infect a human (whose normal body temperature is 98oF). Flumist is approved for use in people aged 2-49 years old. Common side effects include a runny/stuffy nose, sore throat, and fever. The CDC endorses Flumist as the preferred vaccine for children ages 2-8, as it was shown to have a higher efficacy in this group as compared to the traditional flu shot.9,10,11 However, Flumist is contraindicated for pregnant women and immune-compromised individuals; in fact, if you receive the nasal mist it is recommended that you avoid contact with immuno-suppressed individuals for a week after getting the vaccine. This precaution is due to the small chance of the weakened virus being passed to these individuals.
With so many options available, there is really no excuse for healthy people not to get a flu shot. Remember, babies under 6 months old and the immune-compromised cannot be vaccinated. We want to protect these people through herd immunity, which only works if enough people get vaccinated.4 The number of flu-related deaths varies from year to year because of the nature of influenza: the virus is constantly changing through mutations and antigenic reassortment12 (which is why we need a new vaccine every year). The “CDC estimates that from the 1976-1977 season to the 2006-2007 flu season, flu-associated deaths ranged from a low of about 3,000 to a high of about 49,000 people” in the United States.13 Getting vaccinated is an easy way to help protect yourself, your loved ones, and your community.
References/ Further Reading:
10. Belshe RB, Edwards KM, Vesikari T, et al. 2007. Live attenuated versus inactivated influenza vaccine in infants and young children. N Engl J Med. 356:685–696.