Abstract: The present invention provides a vaccine accelerator factor (VAF) which is an in ovo nucleotide immuno-stimulant. The VAF contains one or more DNA constructs, each having a DNA molecule and a vector. Each of the DNA molecule contains one or more genes or gene fragments, each encoding an antigenic peptide of an avian virus. The VAF is preferably administered to the amniotic fluid of an egg after being fertilized for about 17–19 days. The VAF can be co-administered with a viral vaccine containing one or more attenuated or inactive avian viruses. Alternatively, the VAF can be administered prior to the administration of the viral vaccine, which is administered at hatch or post-hatch. The VAF stimulates and accelerate a protective immune response of a viral vaccine.