Kitten deaths have been reported in households of fully vaccinated cats, possibly because of exposure to large amounts of virus in the environment.Infection occurs when the virus enters the body through the mouth or nose. Whether illness results or not depends on the immunity in the victim vs. the number of individual virus particles (i.e. the amount of virus) entering the body. Clinical signs
The clinical manifestations of FPLV are variable based on the dose of the virus, the age of the cat, potential breed predispositions, and prior immunity from maternal antibodies, previous exposure, or vaccination. Most infections are subclinical, as evidenced by the high seroprevalence of anti-FPV antibodies among some populations of unvaccinated, healthy cats. The cats that become clinically ill are usually less than one year old, but older cats are also at risk. There is high mortality in clinically affected kittens and sudden death can occur.Clinical signs usually develop in 4–6 days after exposure, but can show in 2–14 days. The virus infects and destroys actively dividing cells in bone marrow, lymphoid tissues, intestinal epithelium, and—in very young animals—in the cerebellum and retina. The virus primarily attacks the lining of the gastrointestinal tract, causing internal ulceration and, ultimately, total sloughing of the intestinal epithelium. Primary signs include: 

anorexia
lethargy
profuse watery to bloody diarrhea (bloody diarrhea is more common in dogs with parvovirus than cats)
vomiting (most common in cats)Clinical laboratory findings include (but are not limited to):
electrolyte and total protein concentrations that reflect dehydration, vomiting, and diarrhea.
For cats older than 16 weeks, 2 doses, 3 to 4 weeks apart is generally recommended, followed by a 6-month to 1-year booster. Thereafter, a booster vaccination every 3 years is usually recommended; a blood titer test can be done to determine individual antibody levels for catering the timing of boosters. References
External links
Feline Distemper (Panleukopenia) from The Pet Health Library
How to Limit Parvo in Shelters, Rescues and Transfer Animals