Corona is a virus that only affects puppies younger than 8 weeks old. They tried to do a duration of immunity trial on the corona vaccine, and they had to quit because they could not induce any of the dogs, vaccinated or not, to get the disease.
I chose to go with what experts in the field have to say. Here's a couple.
I went to a lecture by Dr. Ron Schultz, the premiere researcher in veterinary immunology and immunization. He called corona "a vaccine in search of a disease." That's a direct quote. And here is an interesting bit from the handout he gave us on vaccine guidelines, where it talks about the corona vaccination. This also mentions the relationship between corona (CCV) and parvo (CPV-2)
"Not Recommended: Prevalence of clinical cases of confirmed CCV disease does not justify vaccination. Clinical disease rarely occurs and when seen is typically mild and self-limiting. Experience has shown no additional increase in infectious enteritis among adults or puppies subsequent to discontinuing CCV vaccine. Neither the MLV vaccine nor the killed CCV vaccines have been shown to significantly reduce disease caused by a combination of CCV and CPV- 2. Only CPV-2 vaccines have been shown to protect dogs against challenge when these two viruses are used.** DOI cannot be determined because in studies performed to date, neither vaccinates nor control dogs developed clinical evidence of disease following experimental virus challenge."
Here is a good quote from Dr. Bob Roger's website. http://www.critteradvocacy.org/K9%20Recommendations.htm
Canine corona virus is only a disease of puppies less than eight weeks of age (15- p20). It is a rare, self-limiting disease (i.e. dogs get well in 3 days without treatment)(3). Corona virus does not cause disease in adult dogs. Cornell University and Texas A&M University have only diagnosed one case each in the last 7 years. For a veterinarian to make a diagnosis of Corona Virus based on clinical signs is highly presumptive. Only electron microscopy of *** can verify the presence of canine corona virus. This is only done at places such as Texas A & M Diagnostic Laboratory, and they report no positive tests. The presence of the virus does not indicate it is the cause of disease. Dogs over 8 wks of age cannot and have not been experimentally induced to exhibit disease from corona virus. This is age related immunity.
Immunologists have reason to believe that the vaccine does not work. Mucosal secretory IgA antibodies would be necessary to protect a dog against this disease & an injectable vaccine will not provide this type of protection.(13, 19- p18, 21) I see no justification for the use of corona virus vaccine.
In 1985 a significant number of dogs (>189) died from encephalitis caused by Corona Virus vaccine, combined with the Rockborn strain distemper. (3, 21) An unfortunate & heartbreaking catastrophe caused by an unnecessary vaccine.