- Health
Flu shots don’t contain dogs as ingredients; cell lines of canine origin are used during the manufacturing process and eliminated from the final vaccine product
Key takeaway
Some vaccines require the production of viruses, which can only be replicated with the help of living host cells. The flu vaccine Flucelvax/Optaflu’s manufacturing process uses a cell line of canine origin grown in Petri dishes. These cells and cell debris are removed during the vaccine-making process through several steps of filtration, centrifugation, and enzyme-based DNA degradation.
Reviewed content
Verdict:
Claim:
Dogs are an ingredient in flu shots
Verdict detail
Factually inaccurate: The final flu vaccine product doesn’t contain cells or tissues from dogs. The manufacturing process uses a cell line of canine origin during the initial steps, but those cells are removed from the final product.
Full Claim
Dogs are an ingredient of flu shots
Review
A Facebook post from November 2024 claimed that dogs are an ingredient in the influenza vaccine, commonly known as the flu shot. The post also implied that this could pose a health risk, questioning the potential consequences of “mass innoculating [sic] a population with dog DNA.”
This claim bears similarities to previous assertions about vaccines containing human fetal tissues or DNA, which were later debunked by Science Feedback. By suggesting that vaccines are made with controversial or unnatural ingredients, these claims may be an attempt to deter people from vaccination. In this article, we’ll show why the claim about dogs is inaccurate and reflects a misunderstanding of vaccine manufacturing processes.
Most of the influenza vaccines distributed in the U.S. are inactivated vaccines. This means that they contain whole viruses that have been chemically “killed” but retain the ability to train our immune system and fight off the flu. Viruses can only replicate inside of cells. Therefore, the flu viruses used to make the vaccines first need to be mass-produced in cells.
Usually, manufacturers use fertilized chicken eggs to produce the viruses before inactivating them. This procedure, which has been used for decades, offers an effective way to replicate the viruses. However, this approach has limitations. Contrary to general belief, the risk of egg allergies isn’t one of them.
The first limitation is that egg-based production requires a large number of eggs and thus cannot be easily scaled up when the demand for vaccines suddenly increases.
Second, the virus might mutate while replicating in the egg. These genetic mutations improve the virus’ adaptation to the egg environment, but can make it less similar to the flu virus circulating in the human population. As a result, the vaccines may lose some effectiveness in protecting humans against the flu[1].
To circumvent the limitations of egg-based vaccines, manufacturers developed cell-based flu vaccines, where the viruses are replicated in cell lines—cells grown in a Petri dish— instead of eggs. The cell-based flu vaccine is commercialized under the name Flucelvax in the U.S. and Optaflu in other countries.
To make this vaccine, the flu virus is replicated in a cell line obtained from a dog, hence the post’s claim that dogs are used in flu vaccines. However, this doesn’t mean that dogs or dog cells are ingredients in the vaccine.
First, the cell line used, called MDCK (Madin Darby Canine Kidney), was harvested from a single Cocker Spaniel in 1958 and has been grown in laboratories since then. Therefore, the production of cell-based vaccines doesn’t require further, repeated harvesting of dog cells or tissues.
Second, these cells are only used to produce the virus and are removed during the manufacturing process, thus they don’t enter the final product. It’s similar to the fact that we use soil to grow maize, yet we don’t eat that soil when consuming corn cobs.
A document from the pharmaceutical company Merck illustrates the purification process of cell-based vaccines. After producing the virus, the cells are filtered out by centrifugation and filtration. Subsequently, steps of ultrafiltration/diafiltration and enzyme-based DNA degradation help remove the remaining cellular debris and DNA.
Therefore, the final vaccine product doesn’t contain MDCK cells or cell debris. The vaccine package insert of Flucelvax/Optaflu specifies that the final vials only contain residual amounts of MDCK-originated proteins and DNA fragments. A study that analyzed the manufacturing process of that vaccine reported an amount of MDCK DNA lower than 10 picograms per dose (one picogram is one hundred-billionth the size of a gram). For context, a 500g beef steak contains about one gram of DNA. ,The study also found that the risk of encountering an MDCK cell in a vaccine dose was 1 in 1034.
In summary, cell-based vaccines use cells of human or animal origin that were isolated decades ago. The vaccine manufacturing process contains several steps to remove all cells, cell debris, and cell DNA. Thus, cell-based vaccines like the flu vaccine Flucelvax/Optaflu don’t contain human or animal tissues.
REFERENCES
- 1 – Rockman et al. (2022) Cell-Based Manufacturing Technology Increases Antigenic Match of Influenza Vaccine and Results in Improved Effectiveness. Vaccines.
