What Types of Flu Vaccines Does CVS Use?

CVS pharmacies carry several distinct types of flu vaccine each season, not just one. The specific options typically include standard-dose egg-based shots, high-dose formulations for adults 65 and older, adjuvanted vaccines that use an immune-boosting ingredient, recombinant vaccines made without eggs entirely, and cell-culture-based vaccines that sidestep some of the drawbacks of traditional egg-grown production. Which one you receive depends on your age, health status, and what the pharmacy has in stock at the time of your visit.

Standard-Dose Inactivated Vaccines

The most widely available flu shot at any pharmacy, including CVS, is the standard-dose inactivated influenza vaccine. These are grown in fertilized chicken eggs, a method that has been the backbone of flu vaccine manufacturing for decades. The virus is grown inside the egg, harvested, purified, and then inactivated so it cannot cause infection. Each dose contains 15 micrograms of hemagglutinin (the protein on the surface of the flu virus that your immune system learns to recognize) per strain.

Standard-dose shots are approved for most people six months of age and older, though pharmacy-administered vaccines are subject to state-level age restrictions. In many states, pharmacists can vaccinate children as young as three, while others set the minimum higher. CVS pharmacists follow whatever their state’s scope-of-practice rules allow.

For healthy adults under 65, the standard-dose vaccine remains a perfectly reasonable choice. Federal immunization advisors do not express a preference for one vaccine type over another in this age group, so the standard egg-based shot is considered interchangeable with cell-based or recombinant alternatives for most younger adults.

High-Dose Vaccines for Older Adults

As you age, your immune system produces a weaker response to a standard flu shot. High-dose vaccines were designed to address that gap. The high-dose formulation contains four times the hemagglutinin per strain compared to the standard shot. A large randomized trial in adults 65 and older found that the high-dose vaccine induced significantly higher antibody responses and provided better protection against laboratory-confirmed influenza illness than the standard dose did.¹

The practical benefit of that stronger immune response has been studied further in real-world settings. A meta-analysis pooling data from five randomized trials found that the high-dose vaccine reduced hospitalizations for pneumonia and influenza by roughly 24% compared to the standard dose and cut all-cause hospitalizations by about 7%.² That pneumonia-and-influenza reduction is meaningful for older adults, who face the highest risk of being hospitalized and dying from flu complications.

However, the picture is not as clean as it might seem. A more recent large trial found that while high-dose vaccine reduced influenza-specific hospitalizations by about 44% relative to the standard dose, the broader measure of hospitalization for any cardiorespiratory cause showed a much smaller gap, and there was no significant difference in death rates between the two groups.³ Another observational study found that the incremental benefit of the high-dose vaccine was limited even among the highest-risk individuals.⁴ So the high-dose shot clearly does more against confirmed influenza, but its effect on total hospital visits and mortality is modest. That is still enough for federal advisors to preferentially recommend it for older adults, as described below.

Adjuvanted Vaccines

An adjuvant is an ingredient added to a vaccine to boost the immune response. The adjuvanted flu vaccine available at CVS uses an ingredient called MF59, a squalene oil-in-water emulsion. Rather than simply increasing the amount of antigen the way a high-dose shot does, the adjuvant works by drawing more immune cells to the injection site and helping those cells process the vaccine antigens more effectively.⁵

This matters because the conventional flu vaccine is roughly half as effective in older adults as it is in younger people. The MF59 adjuvant increases the quantity of antibodies produced and also broadens the quality of the immune response, potentially offering some cross-protection against flu strains that drift slightly from the vaccine strains.⁶ That cross-strain benefit is particularly appealing given that flu viruses mutate constantly and the vaccine does not always match the circulating strains perfectly.

The adjuvanted vaccine is approved specifically for adults 65 and older, so you will not be offered it if you are younger. It sits alongside the high-dose and the recombinant vaccine as one of three options that federal advisors prefer for that age group.

Recombinant Vaccines

Recombinant flu vaccines take a completely different manufacturing approach. Instead of growing the flu virus in eggs or cells and then inactivating it, the recombinant process uses insect cells and a baculovirus expression system to produce large quantities of the hemagglutinin protein on its own. No flu virus is involved in production at all.⁷

This has two practical advantages. First, the vaccine contains no egg protein whatsoever, which matters for people with egg allergies (though as we will see, egg allergy is less of a barrier to flu vaccination than most people think). Second, and arguably more important from a population standpoint, the recombinant process avoids “egg adaptation.” When flu viruses are grown inside chicken eggs, they sometimes mutate to grow better in that environment, and those mutations can change the very surface proteins the vaccine is supposed to teach your immune system to recognize. The recombinant approach sidesteps that problem entirely because no virus is grown in eggs.

The recombinant vaccine is approved for adults 18 and older. For those 65 and older, it is one of the three preferentially recommended options.

Cell-Culture Based Vaccines

Cell-based flu vaccines occupy a middle ground between traditional egg-based production and the recombinant approach. Instead of growing the flu virus in eggs, manufacturers culture it in mammalian cells (specifically, Madin-Darby Canine Kidney cells). The virus still needs to be grown and then inactivated, but because the cells are mammalian rather than avian, the virus does not undergo the same egg-adapted mutations that can reduce vaccine effectiveness.

Research has shown that cell-derived seed viruses eliminate the potential for egg-adapted antigenic changes, and the resulting vaccine more closely matches the strain that international surveillance teams originally selected.⁸ During seasons dominated by H3N2 strains, which are particularly prone to egg adaptation, the cell-based vaccine has been associated with improved effectiveness compared to egg-grown versions.

Cell-based vaccines are approved for people four years of age and older. They are not among the three preferentially recommended options for adults 65 and older, but they remain a solid choice for younger adults and adolescents.

How Flu Strains Are Chosen Each Year

Regardless of which vaccine technology you receive at CVS, they all target the same set of influenza strains for a given season. Flu viruses evolve constantly through antigenic changes, so vaccine composition is reviewed before every flu season. Laboratories contributing to the World Health Organization’s Global Influenza Surveillance and Response System monitor circulating viruses year-round, and vaccine strains are selected months in advance to allow time for manufacturing.⁹

For the Northern Hemisphere, the WHO typically makes its strain recommendation in February, and manufacturers then have roughly six to eight months to produce, test, and distribute vaccines before flu season picks up in the fall. That time lag is one reason the vaccine sometimes mismatches the strains that end up circulating. By the time October arrives, the virus may have drifted from what was predicted in February. This is an inherent limitation of the current system, regardless of whether the vaccine is egg-based, cell-based, or recombinant.

Current flu vaccines in the United States are quadrivalent, meaning they cover four strains: two influenza A subtypes and two influenza B lineages. Every manufacturer uses the same WHO-recommended strains, so the difference between vaccine types is not which strains they target but how those strains are produced and delivered to your immune system.

Which Vaccine Is Recommended for You

For most healthy adults under 65, the Advisory Committee on Immunization Practices (ACIP) does not express a preference for one flu vaccine over another. Standard-dose, cell-based, and recombinant vaccines are all considered equally acceptable, and the overriding recommendation is to get whichever flu shot is available rather than delay vaccination waiting for a specific type.¹⁰

The one exception to this “no preference” stance is for adults 65 and older, where ACIP preferentially recommends one of three enhanced options: the high-dose inactivated vaccine, the recombinant vaccine, or the adjuvanted vaccine. If none of those three is available when a senior has the opportunity to get vaccinated, ACIP still recommends any other age-appropriate flu vaccine rather than no vaccine at all.¹⁰ The message is consistent: the best flu shot is the one you actually get.

When you schedule a flu vaccine appointment at CVS, the pharmacist will generally ask your age and screen for relevant health conditions, then select the appropriate vaccine. If you are 65 or older, you should expect to receive one of the three preferred options. If you are under 65 and have a strong preference for, say, the cell-based or recombinant version, it is worth asking whether it is in stock, since not every location carries every type at all times.

Egg Allergies and Flu Vaccines

Many people with egg allergies have historically avoided the flu shot out of fear of an allergic reaction, since most flu vaccines are produced in eggs. This concern was understandable but is now outdated. Research has established that egg-allergic patients, even those with significant allergies short of anaphylaxis, can safely receive the standard egg-based flu vaccine without special precautions.¹¹ Studies have confirmed that egg-allergic patients without a history of anaphylaxis to egg can be vaccinated safely in a primary care or pharmacy setting.¹²

That said, if your egg allergy is severe enough that you have experienced anaphylaxis from egg exposure, you and your doctor may prefer the recombinant vaccine, which contains no egg protein at all. The cell-based vaccine also has substantially less egg protein than traditional egg-grown vaccines, though it is not entirely egg-free in all cases because some manufacturers still use egg-based seed viruses in earlier production steps. If you have a severe egg allergy and want to be certain, specifically requesting the recombinant vaccine is the most straightforward route.

Getting Your Flu Shot and COVID Booster Together

A common question at the pharmacy counter each fall is whether you can get your flu shot and COVID booster at the same visit. The answer is yes. CVS and other pharmacies routinely administer both vaccines on the same day, typically one in each arm. Early research suggests that receiving both shots simultaneously does not weaken the response to either vaccine. In fact, one study found that concurrent administration of COVID and influenza vaccines was associated with higher and more durable antibody responses to the SARS-CoV-2 spike protein compared to getting the two shots at separate visits.¹³

Side effects from getting both shots at once are generally similar to what you would expect from either shot alone: soreness at the injection sites, mild fatigue, and occasionally a low-grade fever. Some people report feeling a bit more run down after two shots in one visit, but the convenience of knocking out both vaccinations at once tends to outweigh that minor downside. Fewer trips to the pharmacy also means fewer chances to procrastinate and end up unvaccinated when flu season peaks.

What CVS Actually Has on the Shelf

CVS does not manufacture vaccines. It stocks whatever formulations are commercially available each season from the major vaccine manufacturers. In practice, this means the selection at any given CVS location depends on supply agreements, seasonal allocation, and how far into flu season you are visiting. Early in the season, a CVS might carry three or four different vaccine types. Later, as inventory thins, fewer options remain.

If you walk in without an appointment, you will receive whichever vaccine is appropriate for your age group and in stock. If you schedule through the CVS website or app, the booking system typically asks basic screening questions, including your age and whether you have relevant allergies, and routes you toward the right product. But “the right product” mostly means “the right category”: if you are 65 or older, you will be directed toward one of the three enhanced vaccines, but you may not get to pick among those three.

State regulations also play a role in who can receive a vaccine at CVS. Pharmacist-administered vaccination rules vary by state, particularly for children. Some states allow pharmacists to vaccinate children as young as three, while others require a prescription or limit pharmacy vaccination to older adolescents and adults.¹⁴ If you are trying to get a young child vaccinated at CVS, check your state’s rules or call the pharmacy ahead of time.

Why Egg Adaptation Still Matters

One of the less obvious factors behind the push toward cell-based and recombinant vaccines is the egg-adaptation problem, and it is worth understanding because it affects how well any flu season’s vaccine works for everyone. When a flu virus is placed in a chicken egg to grow, it sometimes picks up mutations in the hemagglutinin protein to better attach to the avian-type receptors inside the egg. Those mutations can change the shape of the very protein that your immune system needs to learn to recognize. If the vaccine virus looks different enough from the wild virus because of those egg-adapted changes, your antibodies may not recognize the actual circulating strain as well.⁸

H3N2 strains are the worst offenders here. They tend to mutate more readily during egg passage, and H3N2-dominant flu seasons are often the ones with the lowest overall vaccine effectiveness. Cell-based and recombinant vaccines offer a way around this, since neither relies on growing the virus in eggs. That does not guarantee a perfect match with circulating strains, because the virus can still drift between the February strain-selection meeting and the fall flu season. But it removes one layer of mismatch that is entirely a manufacturing artifact rather than a biological inevitability.

For most people, this distinction is academic: you get whatever shot is available and move on. But if you follow flu-season effectiveness reports and notice years where the vaccine performed poorly, egg adaptation is often part of the explanation. It is one of the reasons the field is gradually moving toward non-egg platforms, even though egg-based production remains the dominant method worldwide because of its scale and cost advantages.

The Adjuvant Debate and Broader Immune Boosting

The MF59 adjuvant used in the adjuvanted flu vaccine is sometimes confused with adjuvants used in other vaccines, and some people worry that the addition of an adjuvant means more side effects. In reality, the MF59 squalene emulsion has been used in flu vaccines in Europe since the late 1990s and has a well-established safety profile. Its mechanism is relatively targeted: it amplifies the influx of immune cells to the injection site and increases the differentiation of those cells into the types that can process and present the vaccine antigen to the rest of the immune system.⁵ It does not act as a broad immunostimulant that revs up the entire immune system indiscriminately.

Research has shown that MF59 enhances the immune response both in quantity (higher antibody levels) and in quality, producing a broader antibody profile that may cover variant strains better.⁶ The adjuvanted vaccine tends to cause slightly more injection-site soreness and redness than a non-adjuvanted shot, which makes sense given that the adjuvant is literally designed to attract more immune cells to the injection area. But these local reactions are generally mild and resolve within a day or two.

For adults 65 and older who are choosing between the high-dose, adjuvanted, and recombinant options, there is no strong head-to-head evidence showing that one consistently outperforms the others in preventing hospitalization or death. The ACIP recommendation treats all three as essentially equivalent for that age group, and the choice often comes down to what the pharmacy has available. If you are in the 65-and-older bracket and a CVS pharmacist offers you any of the three, you are getting a vaccine that federal experts consider appropriate for your situation.