"There are dissenting opinions and practitioners who believe that relaxing the recommendation from every year to every three
years will lead to breakthroughs in population immunity. Should we go back to vaccinating dogs every year?" she asks. "There
certainly is a lot of evidence that the immunity induced by proper vaccination does last many years, even to the point that
several vaccine manufacturers have demonstrated through clinical trials that dogs retain immunity and have even put labels
on their parvo vaccines stating that it could be administered every three years.
"There's a lot of evidence on one hand to support every three years, but a lot of opinions on the other side saying it could
lead to trouble," she adds.
Weather may be affecting the number of cases, Schultz says, since a very wet spring or fall can cause cases to spike. The
virus remains viable in soil for at least a year—or up to three. As the ground dries, the virus isn't readily available, but
once the rain comes, the virus can be reactive and pose a threat to any unvaccinated dogs. Adult dogs that have never been
vaccinated may not show clinical signs of the disease after infection, but will shed a large amount of the virus, he adds.
Schultz says a properly vaccinated dog will have immunity to the virus for life. Involved in the isolation of canine parvovirus
2A in 1978, Schultz says he has kept close watch on the newer strains (2B in the 1980s and 2C in 2005-06) and has found all
the current vaccines provide the same protection against all three.
There is an exception for non-responders, which Schultz says are one in 1,000 dogs. When the virus first emerged, 50 - 75
percent of puppies in litters from Rottweilers and Dobermans were non-responders due to a genetic trait. But today, the idea
that some breeds are more susceptible to infection than others is "an old wives' tale," he says. He has seen some outbreaks
that affected some breeds more than others, but typically that has been because they were breeds used for dog fighting or
similar uses and had never seen a veterinarian or been vaccinated.
"Because parvo was so prevalent in the late 1970s, today we don't have any more Rottweilers or Dobermans that are non-responders.
The genetics were wiped out through Mother Nature, killing them all," he says. But for the random non-responders in the general
population, the virus can be deadly.
"Those dogs that are non-responders, no matter what you do, you can't keep them alive," Schultz says. "They will die."
But any dog that survives infection or is properly vaccinated develops a life-long immunity to the virus, he says.
"What we're seeing right now, because of the economy, is more and more abuse of vaccines in vaccination clinics ... overuse
of vaccines," he says. "When you have a vaccine that can provide a lifetime of immunity, what we recommend in our guidelines
... is that after you complete the puppy series at 14 to 16 weeks, revaccinate at a year and then not any more often than
three or more years. And lots of veterinarians are still vaccinating annually."
Animals vaccinated too often can run the risk of developing adverse reactions, such as auto-immune disorders and hypersensitivity
reactions, Schultz warns.
"Vaccines are, in general, fairly safe," he says. "But they are something you don't want to use if you don't need to."
A better solution to vaccinating annually would be to figure out a way to make sure all dogs get the vaccine at least once
in their lifetime, he says.
"All they would have to do is get one dose at 16 weeks of age or older and it would make such a difference for the entire
population of dogs, because you would have herd immunity," Schultz says. "We can really go a long way by getting more of the
unvaccinated animals vaccinated at least once. But we can't figure out a way to get all those animals vaccinated.
"There's not a veterinary practice in the United States that would allow a dog or puppy to come in and not get core vaccines,"
Schultz says. "If the animal ever gets to see a veterinarian, they're going to have the core vaccines."