Messenger RNA Vaccines in Meat Animals – How are mRNA vaccines different and are they safe?

The use of messengerRNA (MRNA) vaccines in meat animals and their safety for consumers has come to the forefront of discussions recently debating the safety. There are experts on both sides of the aisle. Proponents say mRNA vaccines hold promise to control and eradicate diseases that pose a significant threat to animal health and producer livelihoods. The opposition fears that meat and milk from mRNA-vaccinated animals could negatively impact consumer health.

To understand how mRNA vaccines are different, we first must understand traditional vaccines and how immunity works.

Vaccines and Immunity

Vaccines help prevent illness by training the body to recognize and fight harmful viruses or bacteria. They work by introducing a non-virulent pathogen (non-disease causing ‘bug’) or part of a pathogen into the body that gives the immune system a ‘picture’ of a specific invader. The immune system then mounts an immune response manufacturing specific cells to either destroy the invader or block the invader from accessing the cells within the body it needs to survive.

Ideally, the injection of a vaccine and training of the immune system then enables the body to respond faster and more efficiently, recognizing the invader as harmful and ‘knowing’ how to stop it, when the body is next exposed to that particular or very similar invader.

Without going deep into the science details basically, in response to a vaccine, the immune system makes memory cells and antibodies that circulate throughout your body ready to identify and rapidly destroy a specific threat to prevent disease.

Types of Vaccines

All vaccines have the same goal – train your immune system to fight a specific disease – but the way they go about it is different. 

Vaccines use a weakened pathogen (live attenuated), inactive pathogen (killed), or parts of the pathogen for this recognition training.

Live-attenuated vaccines use a weakened form of the entire virus or bacteria. This creates a strong and typically lasting immune response since the ‘picture’ shown to the immune system is complete and accurate. In healthy animals, this type of vaccine usually doesn’t cause sickness but can cause problems in the immune-compromised.

Inactivated or killed vaccines, as the name suggests, contain a dead virus or bacteria. There is no way to cause sickness from these vaccines, but the immune system doesn’t respond as strongly so a series of vaccinations are often necessary.

There are also subunit vaccines that contain one part of a pathogen. However, scientists must find the part of the pathogen that leads to the most effective immune response. These are also called recombinant vaccines.

Producing these vaccines is often inexpensive but each has drawbacks according to Dr. David Verhoeven, Assistant Professor of Vet Microbiology and Preventative Medicine at Iowa State University. “All these vaccines require specific cell cultures to grow the pathogen in a lab which is time-consuming.  The weakened pathogens do have the remote possibility of reverting back to their pathogenic form or combining with other pathogens to become a new vaccine-resistant pathogen. The killed and subunit vaccines often don’t produce a strong enough immune response limited vaccine effectiveness with any mutated pathogenic forms. Also, these animal vaccines can take three to five or more years from development to being licensed and available on the market rendering them useless to contain a previously unseen outbreak.”

While these traditionally manufactured vaccines have worked well for most animal pathogens, there are some diseases, porcine reproductive and respiratory syndrome (PRRS), hoof and mouth disease virus, H5N1 influenza, and African swine fever virus, that remain a threat because no vaccine has been effective.

This is where mRNA vaccines could prove especially useful.

mRNA vaccines – How they are different

The job of mRNA (messenger RNA) is to carry instructions directing cells to make proteins that are needed to carry out specific functions. Used in vaccines, the mRNA carries a blueprint to make a specific identifying pathogen protein that the immune system will recognize and neutralize. In effect, the body itself manufactures this part of the pathogen.

This process mimics a viral infection, without causing disease. Because the protein blueprint is just a small portion of the pathogen increasing the amount of the protein present does not cause disease. However, the immune system quickly mounts a strong response recognizing these proteins as foreign and potentially a threat.

No live viruses are grown and time is not needed to deactivate, weaken or kill a virus.

Two forms of mRNA vaccines

Currently, there are two forms of mRNA vaccines – one form is structurally similar to what is normally in the body, and the other form is self-amplifying (saRNA) allowing for higher levels of proteins to be made.

Once the genetic sequence of a pathogen is known, mRNA vaccines can be produced rather quickly. The problem lies in the fact that natural mRNA degrades very quickly and that introduced mRNA is quickly destroyed by abundant enzymes called RNAses. For mRNA vaccines to be effective they need to be packaged in a way that allows them to hang around long enough to instruct cells to make the protein in enough volume allowing the body to produce an effective immune response against the pathogen, noted Dr. Penny Riggs, Associate Research Professor of Functional Genetics at Texas A&M.

“The technology to produce mRNA vaccines has been around for decades. However, the technology enabling the mRNA vaccine not to be immediately rejected is new,” Verhoeven said. Mixing in modified nucleotides, the building blocks of RNA, with unmodified nucleotides allows the mRNA to escape detection long enough to train the immune system for future similar invasions. Packaging the mRNA in a fatty outer shell further also helps it can escape the cellular sensors.

Despite this increased stabilization, mRNA vaccines are eventually destroyed by normal cellular processes, Riggs said.

saRNA differ in that they contain the blueprints for the body to produce more proteins but they do not include modified nucleotides.

Objections to mRNA vaccines

Those with objections to the use of mRNA say modified mRNA from vaccines might be present in the milk and meat humans consume and the potential impacts to human health are unknown. In addition, some are raising concerns that the U.S. food supply would be suspect because other countries may develop and use mRNA vaccines in meat animals.

Dr. R.M. Thornsberry, D.V.M. and chairman of R-CALF USA’s animal health committee, has expressed his concern about mRNA vaccines in livestock. Pointing out that many individuals had adverse reactions and complications and even died from Covid vaccines, he says much more study over many years is needed before the safety of mRNA vaccines will be known. “We just can not say how the modified proteins and lipid shell are impacting people,” Thornsberry said. “Would these things stick around in animals and end up in the meat and milk of animals, we don’t know.”

Thornsberry pointed out that the United States has not approved mRNA injections in cattle, but they are in use on a limited basis in swine. He said the dilemma for beef is that the U.S. is importing more and more beef from many different countries, some of which either already are or plan to begin using mRNA in cattle for such cattle diseases as foot-and-mouth disease and lumpy skin disease.  

“This points to the urgent need for MCOOL (mandatory country of origin labeling),” he said adding, “Consumers deserve the right to choose whether to consume beef from a country where mRNA injections are being given to cattle, and the only way they can have that choice is if Congress passes MCOOL for beef.”     

The US Cattlemen’s Association weighed in on the issue with a news release lately.

“Currently, there are no mRNA vaccines licensed for beef cattle in the U.S. Since little is known about the technology, our organization will be forming a task force to develop a fact- and science-based assessment of the issue. We invite all members of the beef supply chain to participate in these discussions and look forward to identifying ways through legislation, regulation, or voluntary measures to increase transparency in the development and application of livestock vaccines and other gene therapies.

“Consumers deserve to know how their food is produced. USCA will continue to prioritize the safety and transparency of the beef supply chain and advocate for the health and wellbeing of its consumers, as it always has,” said a USCA spokesman in a news release.

Much of the concern surrounding mRNA vaccines has resulted from the pandemic, Riggs noted. “As a scientific community, we have fallen short of explaining how mRNA vaccines are developed, tested, and work so that the general public can understand and weigh the benefits versus risks. Adding in the political debates and vaccine mandates the discussion between heated and contentious, no longer rooted in science.”

Use of mRNA vaccines in animals

Animal vaccines, like vaccines used in people, must be tested to prove they protect from the specific disease or infection and are safe. Safety tests for vaccines in livestock go a step further to include withdrawal times and safety for consumers.

The USDA states, “Withdrawal times are intended to ensure meat, milk, or other products for human consumption from the vaccinated animal are free from adjuvant or vaccine organism contamination.”  This means tests are done to determine the length of time after the vaccine is given when no trace of the vaccine can be identified in any part of the animal, says Verhoeven.

Currently, there are no mRNA vaccines licensed for beef cattle in the U.S. Denice Rackley | Courtesy photo

All vaccines must undergo clinical trials to prove their safety and effectiveness before USDA approval. “Merck’s Sequivity (saRNA vaccine) is currently the saRNA vaccine licensed for use in animals by prescription to protect against swine flu in pigs,” Verhoeven noted. “All the testing and approval has been completed for Sequivity.”

mRNA is present in all species and naturally degrades within minutes to hours. Altered mRNA engineered for vaccines to enhance stability and enable recognition and antibody response remains fragile and is removed by normal cellular mechanisms, Riggs noted. “The estimate is that half of the mRNA from a vaccine is gone in about 20 hours, and completely destroyed within a few days.”

In addition, Verhoeven said the cooking of meat and pasteurization of milk make it highly unlikely that we would be exposed to any small remnant of mRNA livestock vaccine. Add to that our digestive system is also designed to defend us against pathogens and the possibility further declines.

While several mRNA vaccines for use in animals are being studied, there are none approved for use in cattle.

There are many hurdles that need to be overcome before widespread use can occur – the requirement that mRNA vaccines to be kept very cold, warmed and used quickly to avoid degradation as well as efficacy of different types of mRNA vaccines still need to be addressed, Verhoeven said.

Could mRNA livestock vaccines take the place of traditional vaccines? Verhoeven said, “That remains to be seen but benefits do exist.” No live virus is used and manipulated in the lab like traditional vaccines so there is not the possibility of causing that disease. Not needing to grow a virus reduces the manufacturing process to months or days allowing for a quick response to disease outbreaks, Verhoeven noted. Even so, some states are drafting legislation outlawing the use of mRNA vaccines.

 “I am a researcher who has been making vaccines for years and started studying mRNA vaccines before the pandemic. The USDA regulations are in place to ensure our food is safe and secure. Vaccines for food animals have protected them against many diseases, limiting the use of mRNA vaccines now would mean losing a new approach to protecting animals from pathogens that we can’t address with current vaccinations,” Verhoeven noted.

According to Progressive Farmer, a Missouri bill that would have required all beef derived from Missouri cattle to include labels detailing vaccines cattle received throughout their life, among other stipulations, did not make it out of committee this past April.

Similar legislation was been introduced in Arizona, Tennessee and other states to require package labels on products made using so-called “gene therapy” techniques, said Progressive Farmer.

“Merck’s Sequivity (saRNA vaccine) is currently the saRNA vaccine licensed for use in animals by prescription to protect against swine flu in pigs,” Dr. Verhoeven noted.