AAAP: Benefits of Marek’s disease vaccination
Marek’s disease vaccination provides indirect protection for non-vaccinated birds
21 January 2026
1 minute read
By: [Excerpts of a presentation by researchers at the USDA-ARS and the Roslin Institute, UK, at the 2025 annual meeting of the American Association of Avian Pathologists]
Marek’s disease (MD) is currently controlled by highly protective live-attenuated vaccines. Recently, it was found that vaccination not only benefits chickens that have received the vaccine but also reduces disease severity in naïve contact chickens.
A study was done to observe and compare the effect of vaccination in a large-scale experiment assessing the effect of natural transmission through chickens receiving full- and partial-dose vaccination.
A shedder-sentinel challenge model was used to naturally passage Marek’s disease vaccine (MDV) through 10 successive groups. Each group consisted of 10 birds kept in an individual isolator and replicated from three to six times. Birds infected in Passage 1 transmitted virus to recipients in Passage 2, and so on. Variables included vaccination status and dosage (full or 1/10 dosage). MD incidence and feather virus load were assessed for each bird.
Statistical analyses of the experimental data showed that the infection and transmission dynamics of birds that have been inoculated with MDV (Passage 1) differed substantially from those of birds that were naturally infected through contact with infected shedder birds, highlighting the importance of mimicking modes of transmissions representative of field conditions in vaccination experiments. MDV transmission was demonstrated through all 10 passages in both vaccinated groups.
Vaccination with the full recommended HVT dose was found to not only provide direct protection from MD and death to the vaccinated birds, but also indirect protection for non-vaccinated contact birds. This indirect benefit was lost in partial-dosage vaccine groups, highlighting the importance of proper dosage for downstream benefits.
