Garrett and Alisa are newlyweds with a new house and an 8-week-old French bulldog named Boston.

Alisa knows Boston needs to be vaccinated but she has heard that even with vaccinations, Boston should not be allowed outside "for a while." Her question: How long is that? I can understand her confusion. With a little understanding of vaccinations and how they work, "a while" can be more accurately defined.

Vaccinations are powerful tools to prevent several deadly diseases, some of which are untreatable. I can think of no more appropriate example of the saying "an ounce of prevention is worth a pound of cure" than vaccinations.

Essentially, vaccines are biologically active substances designed to stimulate the recipient's immune system in preparation for assault from a particular disease-causing organism. I'll explain how vaccines are used in canines, but keep in mind that there are similarities in vaccine protocols with many different species.

Puppies have inherent protection passed on to them from their mother. This protection is both within the bloodstream before birth and then from the mother's milk during feeding.

The specific antibodies the mother has are related to the organisms she has been exposed to both naturally and through vaccination. When these antibodies are passed to her puppies, they are called maternal antibodies and provide the same protection she possesses to her puppies.

Boston has this protection, but it won't last. A puppy's maternal protection starts to wane at about 4 weeks of age, depending on the individual, and is gone around 14 to 16 weeks. It is somewhere within this 10- to 12-week window that the puppy's immune system must shoulder the load. This is where vaccinations begin.

Vaccinations are given on a schedule and as a series. One vaccine given at 8 weeks is almost worthless. Instead, it is just an early stimulus of the pup's immune system. It must be repeated to be ultimately effective. Understanding this relationship of vaccine timing and repetition is important.

I usually start vaccinations around 8 weeks of age. Any earlier and the antibodies provided by the mother will block any effective antibody development by the puppy's own immune system in response to the vaccine. This maternal blocking, coupled with an immature immune system in an 8-week-old puppy, make the first vaccination minimally effective. The vaccines are repeated then at 12 weeks and 16 weeks as the maternal antibodies are disappearing and the pup's immune system is taking over. I call this time between 6 to 14 weeks the "window of vulnerability."

It is during this time when a puppy has less and less protection from the maternal antibodies and not enough from its own immune system. This is precisely why I advise people to keep their puppies out of public places, where they might contact other dogs. Even the feces of other dogs can harbor potentially bad new diseases such as parvovirus. There is simply no need to tempt fate. Keep them at home until the vaccination series is complete, usually by 16 to 18 weeks, then take them out.

Remember, it all comes back to "an ounce of prevention is worth a pound of cure." And now you know that "a while" means 16 to 18 weeks.

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(Jeff Kahler is a veterinarian in Modesto, Calif. Questions can be submitted to Your Pet in care of LifeStyles, The Modesto Bee, P.O. Box 5256, Modesto, CA 95352.)