How long does it take for the vaccine to become effective?

It takes around 30 days from the last of two vaccine doses to gain maximum effectiveness. So, if rattlesnake season begins in your area around May, you should consider having your first dose in March and the second dose 30 days after that in April.

For horses, three doses are required so, for the example above, the first dose should be administered in February, second dose in March, and the third in April to be effective in May.