^a This is an example of a typical vaccination program. Individual programs are highly variable and reflect local conditions, disease prevalence, severity of the challenge, and individual preferences.

^b Most US commercial broiler hatcheries use an in ovo vaccination system for Marek disease at 17–19 days of embryonation (see egg injection picture). Infectious bursal disease vaccine (mild strain) may be combined with Marek disease vaccines. Vectored vaccines in which Marek disease and fowlpox vaccines have been safely modified to carry immunizing antigens for laryngotracheitis, Newcastle disease, or infectious bursal disease are also commonly used in ovo or in day-old chicks. Connecticut strain is often combined with Massachusetts. Bronchitis vaccine is usually combined with Newcastle. Other bronchitis strains specific to the given region are sometimes included. Vaccinations at 14–21 days are optional. A single drinking-water application for Newcastle disease/bronchitis is also common.