Most chickens raised in the United States are not vaccinated against Salmonella. There is no federal law requiring it. Vaccination is voluntary and left entirely to individual producers, and adoption rates remain low across the industry. This stands in contrast to several European countries that have had mandatory national Salmonella vaccination programs for over a decade.
Why Vaccination Isn’t Required
The USDA’s National Poultry Improvement Plan, which sets health standards for breeding flocks and hatcheries, is itself a voluntary program. Producers who participate are not required to vaccinate against Salmonella. A 2024 federal rule update actually proposed removing existing language about vaccination allowances from the plan’s provisions, noting that producers “may choose to vaccinate their flocks for Salmonella typhoid or not with no bearing on the programs’ provisions.”
The FDA’s Egg Safety Rule, which specifically targets Salmonella Enteritidis in shell eggs, takes a similar approach. The rule requires egg producers to follow a set of prevention measures including environmental testing, biosecurity, rodent control, and thorough cleaning. But it does not require vaccination, and vaccinating your flock does not exempt you from any of those other requirements. The FDA has stated that “data on the efficacy of vaccines are not sufficient to allow substitution of vaccination for any of the SE prevention measures.” The agency encourages vaccination as an additional layer of protection but stops short of mandating it.
A Shift May Be Underway
The USDA’s Food Safety and Inspection Service (FSIS) proposed a new framework in 2024 that could change the calculus for producers. The proposal would prevent raw chicken products containing certain dangerous Salmonella strains at or above a specific threshold from entering the market. Three strains of particular concern for chicken were identified: Enteritidis, Typhimurium, and a variant called I,4,,12:I:-.
Here’s why that matters for vaccination: FSIS has acknowledged that vaccination is currently the only pre-harvest intervention that can target specific Salmonella strains. To encourage its use, FSIS began excluding vaccine-related Salmonella subtypes found in raw poultry samples from the calculations used to grade processing plants. This change, effective since April 2024, came after pilot projects at nine processing establishments. In practical terms, producers who vaccinate their flocks won’t be penalized in safety ratings for detecting the vaccine strain itself in their products.
FSIS also stated it is actively engaging with vaccine manufacturers to develop new products, especially modified-live vaccines targeting the specific strains the agency considers most dangerous to people.
How Salmonella Vaccines Work in Poultry
Two main types of Salmonella vaccines are used in poultry. Live attenuated vaccines contain a weakened form of the bacteria that colonizes the bird’s gut and stimulates an immune response without causing disease. These are the most commonly used in the US. Inactivated (killed) vaccines contain dead bacteria and are typically given by injection. Some producers use both types in sequence for stronger protection.
Chicks typically receive their first dose as a coarse spray on their first day of life, either at the hatchery or when placed on the farm. A second dose follows at two to six weeks of age, usually delivered through drinking water. For laying hens that will be kept longer, a third dose may be given around six to sixteen weeks of age. Spray and drinking water delivery are the most common methods because they’re practical and affordable for large flocks. Injection into the breast muscle is a third option but far less common at scale.
Several licensed Salmonella vaccines are available to US producers, primarily targeting the Typhimurium strain. Products from major animal health companies are approved for use starting at one day of age, with booster schedules varying by manufacturer.
What Vaccination Actually Achieves
When producers do vaccinate, the results are significant. A study comparing two integrated poultry operations, one that vaccinated its breeding hens and one that did not, found measurable differences at every stage of production. Vaccinated breeding hens carried Salmonella in their digestive tracts at a rate of 38% compared to 64% in unvaccinated hens. The bacteria showed up in their reproductive tracts just 14% of the time versus 52% in unvaccinated birds.
Those benefits carried forward to the next generation. Broiler chicks from vaccinated breeders tested positive for Salmonella 18% of the time at placement, compared to 34% from unvaccinated breeders. By the time broilers reached the processing plant, Salmonella prevalence on carcasses was 23% for the vaccinated company versus 34% for the unvaccinated one. Environmental contamination on broiler farms was cut roughly in half.
At a population level, countries that have implemented national Salmonella control programs in poultry, which include vaccination as a core component alongside biosecurity and monitoring, have seen dramatic reductions in human illness. Greece’s national program led to a 49% decrease in human infections from the most common poultry-linked Salmonella strain over an eleven-year period. Similar programs across the European Union have driven down human salmonellosis rates substantially since the mid-2000s.
Why the US Lags Behind
Cost and monitoring complexity are the primary barriers. Vaccinating millions of birds adds expense per flock, and tracking vaccinated populations to distinguish vaccine strains from wild Salmonella strains in testing requires additional lab work and coordination. As one industry observer noted, monitoring vaccinated populations “would be” expensive, and the infrastructure to do it at national scale doesn’t currently exist in the US.
There’s also a structural issue. The US poultry industry has historically relied on processing-stage interventions like antimicrobial rinses, chilling protocols, and irradiation to reduce Salmonella on finished products. Vaccination is a pre-harvest strategy that requires action at the farm and hatchery level, adding cost and complexity months before a bird reaches the processing plant. Without a regulatory requirement, many producers have opted not to take on that expense.
The FSIS framework proposed in 2024 represents the strongest signal yet that this may change. By setting enforceable limits on specific Salmonella strains in raw chicken and simultaneously removing regulatory penalties for vaccine strains found in testing, the agency is creating both a stick and a carrot. If the rule is finalized, producers who don’t vaccinate may find it much harder to keep their products on the market.