A Staff Report from the Straight Dope Science Advisory Board

Why do dogs get vaccinated against rabies but not people?

January 19, 2000

Dear Straight Dope:

I go to get my dog vaccinated against rabies, and she's immune if she ever comes in contact with an infected animal. Humans, meanwhile, have to undergo a series of painful, nausea-producing shots when they come in contact with a rabid animal. Apparently there is no preventative vaccine for homo sapiens. Why can't humans get a shot every few years like dogs to eliminate the worry and suffering?

There is a vaccination against rabies for humans, but it's different from the dog version. Rabies (also known as hydrophobia or Lyssavirus) is a very rare disease in humans, so it's not typically vaccinated against. Between 1980 and 1997, there were only thirty-six human rabies cases in the U.S., and they all died. Rabies is one of a number of diseases for which vaccine is produced but not given to the general population because the cost of prevention (three shots, then two boosters if there's an exposure, e.g., an animal bite) is so much higher than immediate treatment following possible exposure (five shots over a month's time). Every year, approximately 16,000 - 39,000 persons in the U.S. get preventative treatment after a possible rabies exposure. That might sound like a lot, but it's still cheaper to give shots after exposure than to vaccinate everybody ahead of time.

Use of the rabies vaccination (pre-exposure) in people is targeted to high risk groups such as some veterinarians, other animal handlers and certain lab workers. International travelers may get vaccinated if they are visiting areas where immediate access to appropriate medical care is lacking and there's a high prevalence of rabies. It's generally not considered to be cost effective to immunize travelers, though, and it's certainly not routine.

From November 1987 to October 1988, of 4,014 Peace Corps volunteers at risk, 175 went in for rabies shots immediately after possible exposure. This is a treatment rate of 43.6 per 1000 volunteers per year, which is very high. These people are at real risk of coming into contact with rabies as it's a common disease in much of the developing world. Still, it was estimated that the cost of pre-exposure vaccination for all Peace Corps volunteers would be 1.8 to 4.2 times greater than the cost of post-exposure treatment, even with the much higher incidence of exposure.

The shots are much better than they used to be and they're now given in the shoulder instead of the stomach. They're not as painful, and are virtually 100% effective if given ahead of time (with boosters if exposed) or immediately following exposure.

According to the January 8, 1999 Morbidity and Mortality Weekly Report (MMWR) from the Centers for Disease Control and Prevention, the cost to a hospital for three doses of intramuscular vaccine is about $220. "A conservative estimate of the cost of i.m. vaccine per life saved can be based on the assumption that universal vaccination of 10,000 people at risk each year would save one more life over 70 years: $220 x 70 (years) x 10,000, or $154 million," the report says. Even if they used the slightly less effective, much less costly intradermal vaccine, the figure would be $15 million.

According to the MMWR, of the thirty six human cases in the U.S., two were attributed to contact with U.S. domestic dogs, twelve were from dogs outside the U.S. and twenty one were from exposure to bat variant rabies (that adds up to thirty five . . . they didn't say where the last case came from).

Rabies is an incredibly nasty disease. It's a virus that infects the brain and kills virtually everybody who contracts it if they're not treated soon after exposure. The incubation period is usually two to eight weeks, but can vary from four days to a year or possibly more, depending on the severity of the wound. Once you become symptomatic, you're pretty much dead meat. First you get a headache and fever, then a sense of apprehension and sensory changes, and then it progresses to spasm of the swallowing muscles (this is where the "hydrophobia" comes from), paralysis, delirium and convulsions. Most people--probably thankfully--die within a week after symptoms appear.

SDSTAFF David comments:

I was just reading a book dealing with AIDS (by Luc Montagnier) and he mentioned, as an aside, that the "cure" given to people for rabies is actually the vaccine, which works because the disease is usually so slow in acting (as you've mentioned). I just thought that was interesting

SDSTAFF Jill replies:

Yes, pre-and post-exposure vaccine are the same, except that if you aren't vaccinated ahead of time with the three doses, you also get RIG after the exposure, which I think stands for Rabies Immune Globulin, along with the same vaccine (five doses). There are two kinds of vaccine on the market. Can you call it a "cure" if it only works if used well before symptoms appear? I don't know for sure. How quickly rabies takes hold (from as soon as four days to over a year) depends on how severe the bite or exposure was,the site of the wound in relation to the richness of the nerve supply and its distance from the brain. If somebody gets bitten by an animal and the animal's rabies status is unknown, intact brain tissue is needed to test for the virus. Whenever I'm in our office in Santa Fe, I hear phone conversations about logistics for sending frozen skunk and raccoon heads around to labs. This is what makes public health the fascinating field that it is.

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