Newcastle Vaccine Frequency Question

[Chans Farm]

I have 61 chicks. They are 17 days old now. We vaccinated them on the 4th of this month. The farm supply company insisted that they had vaccinated them as well, upon the birds arriving on the 25th of March.



The vaccine we used was kept cold, and once mixed was to be used within two hours, or it would be no good. Also, it was, as you can see by the image above, dropped into each of their eyes.

I read here where they should be vaccinated every four months for Newcastle. Is this correct? Or, is once enough?

 

[Eggcessive]

In this link it says every 3 months, but there is another type of vaccine that doesn't need to be repeated in this article from University of Florida:

Newcastle disease

Chickens and turkeys can be immunized against Newcastle disease. Low-virulence live-virus vaccines are administered by a variety of routes such as drinking water, intraocular (eye drops), intranasal (nose drops), spray). Killed-virus oil emulsion vaccines are administered to pullets intramuscularly or subcutaneously as a final vaccine prior to the onset of egg production.
Chicks are often vaccinated at the hatchery against Newcastle disease and infectious bronchitis with a combination vaccine. Day-old poultry vaccinated for Newcastle disease can not be shipped through the mail.
The combination Newcastle-Infectious Bronchitis vaccine can also be given at 10-35 days. The vaccine can be administered via the drinking water, intraocular route or intranasal route. For breeder and layer flocks the vaccine needs to be repeated at 3-month intervals to maintain protective immunity. Alternatively, an inactivated vaccine can be given at the time of housing (18-20 weeks). Further vaccinations should not be required with this procedure. In breeder flocks, the high antibody level obtained by repeated vaccinations will assure transmission of a uniform parental immunity to offspring.
If you purchase pullets or mature chickens to add to your vaccinated flock, they can be vaccinated with Newcastle disease (B-1) vaccine via drinking water, intraocular or intranasal routes. The more reactive LaSota Newcastle disease vaccine is then given 4 weeks later.
Turkeys are often vaccinated against Newcastle disease at 4 weeks of age, and again when the breeders are housed.