U.S.-licensed vaccines currently exist for hundreds of animal diseases. Among these are vaccines for diseases that affect both animals and humans, including rabies, West Nile virus, brucellosis, leptospirosis, and Lyme disease. Preventing these diseases through vaccination can improve the health of the animals at risk and reduce the risk of transmission to humans. In addition, some vaccines are required under state law—all states but Hawaii, for example, require some part of the canine population to be vaccinated against rabies (see, e.g., this chart: Rabies Vaccination and Exemption Laws for Dogs | Animal Legal & Historical Center). Moreover, these vaccines have gone through a rigorous licensing process to ensure that they are safe and effective.
The consequences of non-vaccination can be quite serious. Reported rabies cases in the United States, for example, were up 5.1% in 2023 as compared with 2022, with cats being the most commonly reported rabid domestic animal (see, e.g., Rabies surveillance in the United States during 2023 in Journal of the American Veterinary Medical Association – Ahead of print). The Arizona Game and Fish Department issued a rabies warning in April, noting a rise in animal rabies cases across the state since January 2025. And Nassau County in New York has recently issued a safety alert because of the resurgence in rabies among raccoons, feral cats, and other animals, despite having eradicated the virus from the county in 2016.
When vaccine rates drop, disease outbreaks can occur, which can lead to numerous undesirable consequences, including unneeded expenses, suffering, and animal and human death. One of three CDC-confirmed bat-exposure rabies deaths in 2021, for example, occurred despite testing to confirm the bat had rabies because the person refused vaccination “due to a long-standing fear of vaccines”.
Despite the assurances of safety and efficacy that the licensing process provides, and despite the clear risks to both animals and humans of the disease the vaccines are intended to prevent, animal vaccine hesitancy is on the rise.
So why are cat, dog, and even horse owners expressing increased vaccine hesitancy? And what can manufacturers of animal vaccines do to address the hesitancy and mitigate further risk to animal and human health?
Social media may unduly influence pet owners’ perspectives on whether vaccines are safe or effective—especially when they do not understand the breadth and rigor of the animal vaccine licensing process. Bad information found on social media fuels vaccine hesitancy. Part of what manufacturers need to do to address this hesitancy, then, is to better educate pet owners about the licensing process for animal vaccines.
Licensing Process
Animal vaccines are licensed through the United States Department of Agriculture’s Animal and Plant Health Inspection Service, Center for Veterinary Biologics (access the currently licensed products here: FY2025 Q2 Product Code Book and here Microsoft Word - aquaproducts2008.doc). As part of the application process, manufacturers must conduct a series of studies on the proposed vaccine. The studies necessary for vaccine approval vary based on the qualities of the vaccine itself, as well as the category of animal for which the vaccine is intended.
On the production side, these studies must demonstrate the purity, identity, and safety of the master vaccine stock, and the manufacturer must show that all requirements for the production and storage of that particular type of vaccine have been met. Manufacturers must also submit study protocols that evaluate the immunogenicity and effectiveness of their vaccine stocks, along with the results of those studies. Required safety studies include studies in laboratory animals, studies in targeted animals under biocontainment (which include overdose studies), and field safety studies. If the vaccine is intended for food-producing animals, a study demonstrating the minimum time between vaccination and slaughter is required. If the vaccine is a live virus or live bacterial vaccine, studies on whether the virus/bacteria revert back to a less safe version are required, as are studies that show the amount of virus/bacteria shedding and spreading that may occur in vaccinated animals (access USDA expectations for efficacy studies here: General Licensing Considerations: Efficacy Studies for Prophylactic and Therapeutic Biologics and for safety studies here: Notice announcing portal).
The Center for Veterinary Biologics evaluates all such submissions to determine whether the relevant regulations and requirements have been met. As a part of this evaluation, the Center may require additional revisions, additional studies, or other changes to a manufacturer’s submissions in support of licensure (access the basic license requirements and guidelines for submitting materials in support of licensure here and all Veterinary Services Memoranda here.
Information on the Internet and Social Media
The Problem: The internet and social media, as with most topics, are rife with information on both human and animal vaccines. The difficulty in sifting through fact vs. fiction and what information is reliable contributes to vaccine uncertainty, which is now affecting dog, cat, and horse owners (see, e.g., Assessing vaccine hesitancy and support for vaccination requirements for pets and potential Spillovers from humans - ScienceDirect; Horse Health: Vaccination Woes - Kentucky Equine Research). The accuracy of online information can be hard to distinguish, especially for non-experts browsing social media platforms.
The uncertainty about animal vaccines has negative animal health impacts, and it may lead to a negative domino effect on human health. For example, in one study, 53% of dog owners expressed some hesitancy in vaccinating their dogs. In this same study, 37% of dog owners believed that the rabies vaccination can cause autism in their dogs. If fewer dogs get vaccinated against rabies, there is a greater risk that they might contract rabies and pass it on to humans. Rabies can be fatal to humans if it is not caught in a timely manner (see more discussion of this topic here: Vaccine Misinformation Spilling Over To Pets Puts Us All At Risk).
Proposed Steps to Remedy Hesitancy over the Safety and Efficacy of Human Drugs: These concerns have led to proposed legislation that provides the FDA with broader powers to issue warning letters and civil penalties against those who profit from disseminating false or misleading statements about prescription drugs on social media platforms (access the proposed legislation here: S.5040 - 118th Congress (2023-2024): Protecting Patients from Deceptive Drug Ads Online Act | Congress.gov | Library of Congress).
In draft Guidance for Industry, the FDA is encouraging pharmaceutical companies to address internet-based misinformation regarding their own products by creating safe harbors to do so (see the draft Guidance for Industry here: Addressing Misinformation About Medical Devices and Prescription Drugs: Questions and Answers).
Under the current draft Guidance, a company may be protected from an enforcement action for an online correction related to one of their products if the communication follows the proposed safe harbor exceptions to certain labeling, advertising, and promotional regulations. Typically, such communications and corrections might otherwise be in tension.
The draft Guidance’s examples of what constitutes “misinformation” are instructive. Consider, for example, these two scenarios:
- An influencer tells his followers that he does not like acne drug A because it did not work for his acne and that he recommends acne drug B
- An influencer tells his followers that he does not like acne drug A because it has been shown to cause hair loss and that he recommends acne drug B
The first is an opinion. The second is considered misinformation, which a company might want to address. From there, the Guidance further provides context about what qualifies as a “tailored responsive communication” for which safe harbor is provided, and the company is then under no further obligation to provide ongoing monitoring or follow-up.
Both of these proposals attempt to address social media misinformation surrounding prescription drugs, of which human vaccines are a part. But what about animal vaccines, which are regulated by the United States Department of Agriculture, not the Food and Drug Administration, and which, therefore, are not considered “prescription drugs”?
Could Similar Guidelines and the Assistance of Veterinary Health Professionals Be a Remedy for Animal Vaccine Hesitancy? The proposed Guidelines for Industry, which allow for safe harbors for prescription drug manufacturers, could be adopted almost out of whole cloth by the USDA. That way, animal vaccine manufacturers could similarly address online any social media misinformation about one of their products (see USDA guidelines for advertising and promotional materials here. Animal vaccine manufacturers might consider submitting a request to the USDA for just such a guideline, with analogous safe harbors, so that they may better address the misinformation about their products that may be found on the internet.
Manufacturers also could consider enlisting the help of veterinary professionals. By providing materials to educate veterinary professionals on the factual information about their vaccines, and by encouraging professionals to correct misinformation they see, manufacturers could help address vaccine hesitancy.
The authors of the recent Viewpoints in the Journal for the American Veterinary Medical Association provide two main pathways by which animal healthcare providers can be more proactive in addressing misinformation, improve trust between veterinarians and animal owners, and prevent harm to animal and to human health (Moran & Knesl, How can the veterinary profession tackle social media misinformation? Viewpoint, JAVMA doi.org/10.2460/javma.24.10.0665). The first is how to “pre-bunk” internet misinformation and the second is how to debunk it.
“Pre-bunking” consists of producing videos or posts that (1) correct specific claims or narratives, (2) question sources, or (3) identify and explain logical fallacies. The debunking, on the other hand, consists of fact-checking to ensure that there is a truthful scientific record available. The authors stress that “it is vital that veterinary professionals be proactive in producing publicly available authoritative content countering falsehoods.”
Animal vaccine manufacturers should be aware of increased vaccine hesitancy in pet owners. They should also consider ways to combat the spread of social media misinformation about their products that contributes to this increase. Some form of outreach, whether to USDA or to veterinary care providers, could provide tools for industry to better address the health risks that arise should such misinformation continue to be unchecked.