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Weighing the Differences Between the Nasal Spray and the Traditional Flu Shot

Estimates by the Centers for Disease Control and Prevention (CDC) show that two in three children and one in four adults have strong fears of needles. These fears may cause individuals to delay or even completely skip vaccinations altogether. In recent years, a nasal spray version of the flu vaccine has gained popularity. But should providers be wary of the nasal spray? Or is it just as good (or better) than the flu shot? AFMC’s epidemiologist Kristy Bondurant, PhD, MDH discusses the answers to these questions and more.

Differences

There are quite a few notable differences between the flu shot and the nasal spray:

Administration: The flu shot is injected into the arm of an adult or the leg of a child under age 3. The nasal spray (FluMist) is inhaled through the nose. A traditional flu shot is injected into a more muscular part of the body, such as the upper arm because the vaccine will be absorbed faster. Muscle tissue has a greater blood supply than regular tissue under your skin, allowing the vaccine to get into your bloodstream faster. “Intranasal vaccines,” Dr. Bondurant says, “stimulate an immune response in the mucosal tissue where a virus enters and infects the mucosal tissue of the upper airways.” In other words, the nasal vaccine is being exposed to the direct spot where viral infection starts in your body: in your sinuses and upper airways. “In theory, this allows the body to fight a virus that enters the body through airways more quickly than an immune response generated by an intramuscular vaccine.”

Production: There are three main ways that flu vaccines are made in the U.S.: egg-based flu vaccines, cell culture-based flu vaccines, and recombinant vaccines.
Egg-based vaccines, which have been used for more than 70 years, are used to make both inactivated (dead virus) vaccines and live attenuated (weakened virus) vaccines. According to the CDC, egg-based vaccine production begins with candidate vaccine viruses (CVVs) grown in chicken eggs per FDA regulatory requirements. The CVVs are injected into fertilized chicken eggs and incubated for several days to allow for the viruses to replicate. The viruses are harvested from the eggs, and, for the flu shot, the virus antigen is purified, quality tested, packaged, and distributed across the U.S. For the nasal spray, the CVVs are used to create are used to make live, weakened viruses that are then tested and distributed. The FDA tests and approves all flu vaccines prior to release and shipment.
The FDA approved cell culture-based vaccines in 2012. This manufacturing method is used to make traditional flu shots, not nasal spray flu vaccines. The production process has various steps. First, the CDC uses viruses that have grown in cultured mammalian cells to make CVVs, which are provided to a vaccine manufacturer. The manufacturer injects CVVs into cultured mammalian cells (instead of chicken eggs) so that the virus can make copies of itself for a few days. Then, the virus-containing fluid is collected from the cells, and the virus antigen is purified. The process continues with purification, virus inactivation, and testing. The FDA then tests and approves the vaccine for distribution. Since the 2021–2022 season, this vaccine is completely egg-free.
Recombinant vaccine production was approved in 2013 and does not require CVVs for production. Instead, these vaccines are synthetically created and do not require any live or inactive viruses to be created. Scientists obtain the viruses’ gene that contains the instructions for creating an antigen (the part of a virus that triggers the human immune system to create antibodies). This gene is combined with a baculovirus, which is a virus that only infects invertebrates. The baculovirus helps deliver genetic instructions for making the flu antibodies into a host cell. Once the virus enters a host cell (approved by the FDA), it instructs the cells to rapidly produce the antibodies. The antibodies are grown in bulk, collected, purified, and then packaged. Prior to FDA approval, the vaccine is released to the public. This method also does not require the use of chicken eggs in any part of the process. This is also the fastest method of viral production.

Restrictions: “Because there is an egg-based component to most common vaccines, it is recommended that anyone with an egg allergy consult with their primary care physician ,” Dr. Bondurant says. According to the CDC, patients who can eat lightly cooked eggs, such as scrambled eggs, are unlikely to be allergic to the vaccine. Tolerance to egg-containing foods does not exclude the possibility of an egg allergy or reaction to egg-based vaccines. Providers should encourage patients who are unsure about the extent of their egg allergy to check additional egg-allergy restrictions here.
The traditional flu shot is appropriate for most people. Different flu shots are appropriate for people of different ages. Patients should take the flu shot that is appropriate for their age. Children younger than six months of age are too young to get a flu shot. People with severe, life-threatening allergies to any ingredients in a flu vaccine (other than egg proteins) should not get the vaccine. This includes gelatin, antibiotics, or other ingredients. People who have a severe allergic reaction to any dose of a flu vaccine should not get that flu vaccine again and may not be able to receive other vaccines. It is important that patients talk to providers to ensure which vaccine is the most appropriate for them.
“According to the FluMist manufacturer,” Dr. Bondurant says “those who should not get FluMist (nasal spray vaccine) include those with a severe allergy to eggs or active ingredients in the vaccine, those who are 2–17 taking aspirin (after taking FluMist, no aspirin should be taken for four weeks), and patients under the age of 2. There are several groups who should speak with their provider before considering FluMist,” she adds, “including those with a history of wheezing, those with a weakened immune system, those with certain chronic diseases, pregnant or nursing women, or people taking certain meds.” The CDC includes these precautions as well as further guidance. For additional information on who can and cannot take the FluMist vaccine, check out the FluMist site, or the CDC’s nasal spray guide.

CDC and AAP Preference

The CDC and the American Academy of Pediatrics (AAP) are the only well-established organizations in vaccine research. The CDC does not prefer one vaccine to the other as long as patients take one. While the AAP previously gave preference to the shot over the nasal spray due to its more proven effectiveness, it has more recently accepted both versions as effective. The AAP states that FluMist is more effective than taking no vaccine. The nasal spray may be more practical than the flu shot just because fewer providers will be using the flu shot, so the cost to maintain the nasal sprays may be higher, and fewer of the nasal sprays would be used.

Other Nasal Spray Vaccines

Given that the coronavirus is a respiratory virus that latches onto our cells in the upper respiratory tract, including our nose and throat, it is almost a given that research has begun on a nasal spray version of the COVID vaccine. Though non-human testing has shown some positive results, human trials have failed. “Currently, the only intranasal vaccine approved for use in the U.S. is FluMist for influenza virus” Dr. Bondurant says. “However, there are forms of SARS-CoV-2 intranasal vaccines approved in countries outside of the U.S. There is also research occurring in the U.S. to develop intranasal and oral COVID-19 vaccines. Scientists throughout the world are still studying the effectiveness of intranasal vaccines for COVID-19. “

Storage

Proper storage of vaccines is critical to their effectiveness. “Store FluMist vaccines in a 2–8 refrigerator,” Dr. Bondurant says. “FluMist intranasal vaccines cannot be frozen,” she adds. Keep influenza vaccines stored away from the freezer compartment, the back wall, or the bottom of the refrigerator where temperatures are usually colder. “The shelf life for the nasal spray is usually around 18 weeks for both the nasal spray and the flu shot. For the traditional flu shot, it is June 30 for the upcoming influenza season (i.e., July 1–June 30 of the following year).

While vaccination is critical to preventing viral infection, it’s important to know that vaccines are not 100 percent effective. “Just because you get vaccinated,” Dr. Bondurant adds, “doesn’t mean you’re protected from all infections. You can still get infected.” The hope with the influenza vaccine is that if a patient is infected, they are present with a milder illness. “Some years, the vaccine matches well with the current flu virus, and some years it doesn’t. We still rely on manual vaccine manufacturing processes,” she says. “Scientists have to look at what virus strain circulated last year and make an informed, research-based decision on what will be most effective this year.” Regardless of a patient’s vaccine preference, what’s important is that they get the flu vaccine, not which one they decide to get.

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