Clinical Trial Shows Cell-Based Flu Shot Works Well in Kids

child receiving vaccine

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Key Takeaways

  • A new study has found that a cell-based flu shot works well in children as young as 2 years old.
  • There is just one vaccine of this type that is currently licensed in the United States.
  • Experts say that the new data from the study makes the case for lowering the age for cell-based flu shot for children.

For years, egg-based influenza shots have been the norm. However, there are also other ways to make flu vaccines that do not involve eggs.

A recent study of one alternative—a cell-based flu shot—showed that it's effective at preventing influenza in kids as young as 2 years old. Experts say that the promising results back up the decision of the Food and Drug Administration (FDA) to lower the age for using cell-based shots in kids to help protect them against the flu and its complications. Last week, the organization approved a cell-based option called Flucelvax for kids as young as 6 months.

The Study

The new study, which was published in the New England Journal of Medicine, is the first to look at the absolute efficacy of a cell-based flu shot in children as young as 2 years old.

Currently, the only cell-based flu shot licensed for use in the United States is the Flucelvax Quadrivalent, which is the vaccine used in this study. It is available for children 6 months and up.

The researchers conducted a randomized controlled trial including 4,514 participants in Australia, Thailand, Estonia, Finland, Lithuania, Poland, Spain, and the Philippines to look at the efficacy of a cell-based shot called Flucelvax Quadrivalent across three flu seasons.

The results showed that the cell-based shot was 54.6% effective overall at preventing the flu in children. However, the efficacy varied by flu type.

The study showed that the cell-based shot was:

  • 80.7% effective against influenza A/H1N1
  • 42.1% effective against influenza A/H3N2
  • 47.6% effective against influenza B

The efficacy was the same regardless of the participant’s age, sex, race, and whether they had previously received a flu shot.

How Flu Vaccines Are Made

The FDA has approved three different flu vaccine production technologies in the U.S.:

  • Egg-based
  • Cell-based flu
  • Recombinant flu


Most flu vaccines that are used in the U.S. are created through an egg-based manufacturing process. It starts with the Centers for Disease Control and Prevention (CDC) giving manufacturers candidate vaccine viruses (CVVs) that have been grown in eggs.

The CVVs get injected into fertilized hen’s eggs and are allowed incubated for several days to give the viruses a chance to make copies of themselves (replicate).

While most people do not need to worry about a flu shot being made with eggs, people with egg allergies may need to get a different type of vaccine.

Next, the liquid that has the virus in it is removed from the eggs. If the manufacturer is going to create an inactivated flu virus—which is what flu shots are—the virus is then killed and the virus antigen is purified. The CVVs in the nasal spray vaccine are live but have been weakened (which means that they cannot make you sick).

For the final step, the fluid is put through quality testing and packaging before being distributed.


The cell-based flu shot process is a little different. First, the CDC gives manufacturers CVVs that have been grown in cells. Next, the CVV is put into cells cultured from mammals (instead of putting them in eggs). Here, the viruses are given a few days to replicate.

As with the egg-based vaccines, the fluid is collected from the cells and the virus antigen is purified. Once it’s ready to go, it’s packaged up, tested and checked, before finally heading to distribution.

Flu shots made with a cell-based candidate vaccine viruses can offer better protection than traditional, egg-based flu vaccines because the viruses that are used to make them are often more similar to circulating “wild” flu viruses than the viruses that are used to make egg-based vaccines.


The recombinant flu vaccine does not use a CVV. It’s created with a gene that can provide the genetic instructions for making a surface protein found on influenza viruses called hemagglutinin (HA). It’s this antigen that triggers the human immune system to create antibodies to specifically fight the flu virus.

To produce a vaccine, the gene for making the antigen is put together with a baculovirus (which mostly infects insects and does not cause illness in people). The baculovirus helps get the genetic instructions for making the flu virus HA antigen into the cells in the host cell line, where it quickly starts making the HA antigen.

From there, it’s grown in bulk, collected, purified, and packaged as a recombinant flu vaccine. As with the other vaccines, it’s tested and checked to ensure that it’s ready to make its way to your arm.

Flu Vaccine Recommendations

The CDC recommends that everyone age 6 months and older get a flu vaccine each season (though there are rare exceptions). People with a severe egg allergy should receive either a cell-based flu vaccine or recombinant vaccine (neither of which is made with eggs).

The CDC suggests that you get a flu shot at least by October, if not as early as September.

What Doctors Think

Infectious disease expert Amesh A. Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security, tells Verywell that the study’s findings are “not surprising” given how well cell-based flu vaccines have performed in the past.

“We have seen cell-based influenza vaccines outperform traditional influenza vaccines in adults for some time,” says Adalja. “No flu vaccine is extremely efficacious against mild disease, but when it comes to what matters most—preventing serious disease, hospitalization, and death—the efficacy is much higher than 54.6%.”

Richard Watkins, MD, an infectious disease physician and a professor of internal medicine at the Northeast Ohio Medical University, tells Verywell that, “the results are exciting and hopefully will lead to another option for flu vaccines for children.”

Adalja says that the flu is a “challenging virus” and there are “still limitations on how accurate the vaccine will be” compared to the strains of the virus that circulate each season. That’s why he stresses the importance of getting children vaccinated against the flu.

Richard Watkins, MD

The results are exciting and hopefully will lead to another option for flu vaccines for children.

— Richard Watkins, MD

While it may not entirely prevent a child from getting the flu, Adalja says that getting vaccinated does help prevent them from getting “severe complications of influenza” as well as helps “prevent them from spreading the infection.”

The research is promising, but it remains to be seen what the new data will mean for the future availability of cell-based flu shots for younger children in the U.S.

What This Means For You

The CDC recommends that (with a few rare exceptions) everyone age 6 months and older get a flu shot each year. Talk to your pediatrician about your child’s flu vaccine options.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Nolan T, Fortanier AC, Leav B, et al. Efficacy of a cell-culture-derived quadrivalent influenza vaccine in childrenN Engl J Med. 2021;385(16):1485-1495. doi:10.1056/NEJMoa2024848

  2. Food and Drug Administration. Flucelvax quadrivalent label.

  3. Centers for Disease Control and Prevention. How influenza (flu) vaccines are made.

  4. Centers for Disease Control and Prevention. Cell-based flu vaccines.

  5. Lu HY, Chen YH, Liu HJ. Baculovirus as a vaccine vectorBioengineered. 2012;3(5):271-274. doi:10.4161/bioe.20679

  6. Centers for Disease Control and Prevention. Who needs a flu vaccine.

By Korin Miller
Korin Miller is a health and lifestyle journalist who has been published in The Washington Post, Prevention, SELF, Women's Health, The Bump, and Yahoo, among other outlets.