Flublok and Flucelvax are the two common flu shots made without chicken eggs, and both protect at least as well as standard egg-based shots. They get there in different ways: one is built from a single flu protein made in insect cells, the other is grown from real flu virus in animal cells.1PubMed. FluBlok, a next generation influenza vaccine manufactured in insect cells Those differences shape who can get each one and how strong a response it tends to produce, which is why the better choice depends mostly on your age.
How Each Vaccine Is Made
Your immune system mostly recognizes flu by a protein on the virus’s surface. Flublok contains only that protein. It is made by giving insect cells the genetic instructions to produce it.2PubMed. FluBlok, a next generation influenza vaccine manufactured in insect cells No flu virus is ever grown to make Flublok.3PubMed Central. Unique features of a recombinant haemagglutinin influenza vaccine that influence vaccine performance4PubMed. Technology transfer and scale-up of the Flublok recombinant hemagglutinin (HA) influenza vaccine manufacturing process
Flucelvax takes a different route. It is grown in a line of dog-kidney cells kept in the lab, then the virus is killed and purified.5PubMed Central. Cell culture-derived influenza vaccines in the severe 2017–2018 epidemic season: a step towards improved influenza vaccine effectiveness Your immune system sees pieces of the whole virus, not just one protein, which is a real difference from Flublok’s single-protein design.
Avoiding eggs matters because flu virus grown in eggs can pick up small changes that help it grow there. These changes can make the vaccine strain look slightly different from the flu that’s circulating, and your antibodies may then fit the real virus less well.
The two methods handle it differently. Growing virus in cells avoids the egg changes, though virus grown in any cell can still shift slightly. Flublok never grows virus, so it can’t pick up these changes at all.
Which One Protects Better Against the Flu
In adults 50 and older, people given Flublok were about 30% less likely to get confirmed flu than those given a standard shot.6PubMed. Efficacy of Recombinant Influenza Vaccine in Adults 50 Years of Age or Older In a very large study of adults 50 to 64, Flublok cut confirmed flu by about 15% compared with a standard egg-based shot.7PubMed. Recombinant or Standard-Dose Influenza Vaccine in Adults under 65 Years of Age In that same group, though, Flublok and standard shots did about equally well at preventing flu hospital stays.8Open Forum Infectious Diseases. 2322. Effectiveness of Recombinant Influenza Vaccine vs. Standard Dose Inactivated Influenza Vaccines Against Hospitalized Influenza-Related Outcomes in Adults: A Cluster Randomized Trial
Flucelvax has its own record against egg-based shots. Across three US seasons from 2017 to 2020, it prevented about 10% to 15% more test-confirmed flu.9PubMed Central. Relative Vaccine Effectiveness of Cell- vs Egg-Based Quadrivalent Influenza Vaccine Against Test-Confirmed Influenza Over 3 Seasons Between 2017 and 2020 in the United States In the 2022–2023 season the edge was smaller, about 8%.10PubMed Central. Estimated Relative Effectiveness and Public Health Impact of Cell‐Based Versus Egg‐Based Influenza Vaccines During the 2022–2023 Season in the United States So its advantage is steady but modest, and it varies by season.
A figure like “15% better” is relative to the standard-shot group. It means 15% fewer cases than that group had, not that the shot is 15% effective. Everyone in these comparisons was vaccinated, so both groups started with real protection and the gap sits on top of it.
These percentages each compare one vaccine with a standard shot, in different years and groups, so they don’t rank Flublok against Flucelvax. To do that, researchers would need to give both to similar people in the same season and count who gets flu. Until one is done, both beat standard shots, and neither is proven better than the other at preventing illness.
Why Flublok Tends to Give a Stronger Immune Response
Flublok contains 45 micrograms of flu protein per strain, three times the 15 micrograms in standard shots, including Flucelvax.11Children’s Hospital of Philadelphia. In the Journals: Recombinant or Standard-dose Influenza Vaccine for Adults Under 65? The bigger dose is linked to a stronger immune response.12PubMed Central. Safety, efficacy, and immunogenicity of Flublok in the prevention of seasonal influenza in adults Despite the extra protein, Flublok caused slightly less arm soreness and redness than a standard shot.13PubMed Central. Safety, efficacy, and immunogenicity of Flublok in the prevention of seasonal influenza in adults
Side-by-side blood tests show the difference. When people received one of the two in the same season, Flublok recipients made more antibodies against the H3N2 strain than Flucelvax recipients.14PubMed Central. Comparison of Human H3N2 Antibody Responses Elicited by Egg-Based, Cell-Based, and Recombinant Protein–Based Influenza Vaccines During the 2017–2018 Season Flucelvax recipients that season had low antibody levels against every H3N2 strain tested.15PubMed Central. Comparison of Human H3N2 Antibody Responses Elicited by Egg-Based, Cell-Based, and Recombinant Protein–Based Influenza Vaccines During the 2017–2018 Season In another season, Flublok again produced the highest antibody levels, while cell- and egg-based shots performed similarly to each other.16PubMed. Comparison of A(H3N2) Neutralizing Antibody Responses Elicited by 2018-2019 Season Quadrivalent Influenza Vaccines Derived from Eggs, Cells, and Recombinant Hemagglutinin Flublok also seems to recruit more helper cells: about 78% of Flublok recipients built up immune helper cells against flu, compared with 53% for Flucelvax.17PubMed Central. Recombinant HA-based vaccine outperforms split and subunit vaccines in elicitation of influenza-specific CD4 T cells and CD4 T cell-dependent antibody responses in humans Helper cells are white blood cells that coordinate the immune response, including telling other cells to make antibodies.
Antibody levels suggest how strongly your body responded, but they don’t guarantee protection from illness. Studies that count real flu cases matter more, since they show what happens in everyday life. For Flublok versus a standard shot, the blood results and the case counts point in the same direction. For Flublok versus Flucelvax, only blood results compare them directly, so the stronger response shouldn’t be read as proof of fewer cases.
Who Can Get Each Vaccine
Flucelvax is approved for anyone 6 months and older, after the lower age was dropped from 2 years in October 2021.18PubMed Central. Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices — United States, 2022–23 Influenza Season Flublok is approved for people 9 and older.19U.S. Food and Drug Administration. HIGHLIGHTS OF PRESCRIBING INFORMATION: Flublok For years Flublok was approved only for adults 18 and up, so some pharmacy guidance may still list that age.20PubMed Central. Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices — United States, 2022–23 Influenza Season For children under 9, Flucelvax is the egg-free choice between the two.
Children getting flu vaccine for the first time, or who haven’t had enough doses before, may need two doses at least four weeks apart. Any age-appropriate flu shot is far better than skipping vaccination.
Pharmacies often stock only one or two flu brands, so call ahead and ask for Flublok or Flucelvax by name. State rules limit the ages pharmacists can vaccinate, so a pharmacy may not be able to give a young child any shot.
Egg Allergy and Side Effects
Neither Flublok nor Flucelvax contains egg protein.21The Medical Letter on Drugs and Therapeutics. Flublok vs Flucelvax: How Do They Compare? Studies also show that people with egg allergy are not at higher risk of reactions to egg-based flu shots.22The Medical Letter on Drugs and Therapeutics. Flublok vs Flucelvax: How Do They Compare? So US vaccine and allergy experts say anyone with an egg allergy of any severity can get any flu shot for their age, with no precautions beyond those for any vaccine.23The Medical Letter on Drugs and Therapeutics. Flublok vs Flucelvax: How Do They Compare?
Allergic reactions still happen rarely. In Flublok’s first year on the market, safety monitoring picked up a noticeable number of allergic reaction reports, including one severe reaction.24PubMed Central. Surveillance of Adverse Events After the First Trivalent Infuenza Vaccine Produced in Mammalian Cell Culture (Flucelvax®) Reported to the Vaccine Adverse Event Reporting System (VAERS), United States, 2013-2015 An egg-free shot isn’t allergy-proof, because people can react to other ingredients. If you’ve had a serious reaction to a past flu shot, talk with your doctor before getting the next one.
Most people have nothing worse than minor effects. The most common are a sore arm, mild redness, or swelling where the shot went in. Some people feel tired, get a headache, or have body aches for a day or so. Neither vaccine contains live virus, so neither can give you the flu. Symptoms usually fade within one to two days.
Which to Choose at 65 and Older
CDC recommends people 65 and older get a high-dose shot, an adjuvanted shot, or Flublok rather than a standard-dose shot.25Centers for Disease Control and Prevention. Flu and People 65 Years and Older Studies suggest these work better in older adults, whose immune response weakens with age.26Centers for Disease Control and Prevention. Flu and People 65 Years and Older Each preferred shot tackles this in its own way: Flublok and high-dose shots contain more flu protein, and adjuvanted shots add an ingredient that boosts the response. That makes Flublok a preferred choice at 65 and older, while Flucelvax is not on that list. If none of the preferred shots is available, getting a standard shot is better than waiting.27Centers for Disease Control and Prevention. Flu and People 65 Years and Older
CDC does not rank Flublok, Fluzone High-Dose, and Fluad against each other, so choose whichever is available and covered by your plan rather than waiting for a particular brand. Ideally get it by the end of October.
Cost and Insurance Coverage
Flublok costs more per dose than a standard shot. For adults 18 to 64, the extra cost works out to about $94,000 for each year of healthy life gained.28PubMed Central. Cost-effectiveness of recombinant influenza vaccine compared with standard dose influenza vaccine in adults 18–64 years of age For ages 50 to 64 it drops to about $61,000, making Flublok a better value in that group.29PubMed Central. Cost-effectiveness of recombinant influenza vaccine compared with standard dose influenza vaccine in adults 18–64 years of age Those figures describe value to the health system, not your bill.
Most US insurance plans, including Medicare Part B, cover flu shots at no cost to you. Coverage usually includes Flublok and Flucelvax when you go to an in-network pharmacy or clinic. Without insurance, prices vary a lot between locations, so call ahead and compare.
As a rule of thumb, under 9 means Flucelvax of these two. From 9 to 49, either works, and both beat egg-based shots. At 50 and up, Flublok has the strongest evidence.