Dear Dr. Barchas,

I have two dogs that I adopted on my own from people who did not give them the proper shots, etc., while they were being raised. I have found vaccination schedules for young puppies, but not for older puppies. My Lab mixes are about 6 months old. What shots should they have at this age?

Leenette

Holland, MI

Vaccines are divided into two groups. Core vaccines are critically important, while so-called noncore vaccines are optional immunizations that may be appropriate for some dogs depending on age, lifestyle, and location.

The three core vaccines for dogs are rabies (which is required by law in most developed countries), distemper, and parvovirus. Distemper and parvo are usually combined into a single injection called the DHPP, which also covers hepatitis and parainfluenza.

Noncore vaccines include leptospirosis, Bordetella (which offers some protection, in theory at least, against kennel cough), Lyme, rattlesnake, and a host of others. Over the years, many vaccines du jour — such as the now-withdrawn dental disease vaccine — have fallen in this category.

Although vaccine schedules are still debated among veterinarians, a consensus has developed among most of the well-respected organizations that provide guidance. Previously unvaccinated dogs older than 4 months should receive a single rabies vaccination, followed by a booster in one year. Subsequent rabies boosters should be administered every one to three years as required by law. Be aware that rabies vaccine requirements can be somewhat fluid — legislatures are notoriously fickle and regulations can change, so check with your vet to make sure your pets comply.

The distemper/parvo combination vaccine is not regulated by law. Most experts recommend that unvaccinated older puppies (or adult dogs) receive two DHPPs, separated by two to four weeks. They should get boosters after one year and every three years thereafter at most. No reputable organization with which I am familiar recommends perpetual vaccination; previously vaccinated mature dogs can go more than three years between DHPPs.

Leenette, your dogs may or may not be good candidates for some of these vaccines. Have a comprehensive discussion with your vet about your dogs’ lifestyles, as well as the risks and benefits of optional vaccines, before they are administered. For your information, my pal Buster has not received any noncore vaccines for many years.

There are two other things to discuss with your vet: intestinal worms and heartworm. Dogs from sketchy backgrounds almost invariably will be infested with worms. Some of these worms can pose a significant health risk to humans, but they can be eliminated with readily available medications. Heartworm is a blood parasite of dogs spread by mosquitoes. It can cause heart failure, and treatment options currently are limited by drug supply shortages. Heartworm is easy to prevent with monthly preventative medication, and many heartworm preventatives also remove intestinal worms.

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