Rabies: To Immunize or Not?

Sample scenarios:

  1. You were just bitten by a semi-domesticated coati while in a small village in Costa Rica. The government insists that there is no rabies in Costa Rica and therefore there is no post exposure vaccine available. The coati looks healthy.
  2. While on safari in Kenya you are observing a troop of baboons from the roof  hatch of your Land Cruiser when the person next to you decides to have a  snack. A baboon jumps onto the vehicle and snatches the food and immediately makes its getaway but not before leaving a substantial scratch on your arm.
  3. You are engaged in a research/study program in Australia. One afternoon while working with bats, you receive a bite on your fingertip. You recall reading something saying that there isn’t any rabies in Australia but there is something called lyssavirus.
  4. You gave your leftover lunch to one of the dogs (as you’d seen many Bhutanese do) and received a nip on the hand. The dogs are handsome and appear quite healthy.

Rabies is found on all continents except Antarctica. The World Health Organization estimates that 55,000 people die annually of rabies, 95% of them in Asia and Africa. It is a virus transmitted via the saliva of mammals from bites or scratches. Once symptoms develop, rabies is virtually 100% fatal. The incubation period is typically 1 – 3 months from exposure to symptoms but can vary from less than a week to more than a year. This means that you should not (contrary to myth) observe the animal in question for 10 days to ascertain if it has rabies to decide on whether to undergo treatment. A sick animal may not manifest symptoms within that timeframe and you could become irreversibly sick before the conclusion of the observation period.

While all wild and domestic mammals may carry rabies, 99% of human rabies transmission is from dogs. Most high-income countries have effective pet rabies vaccination programs. Many low-income countries either have no such program or an ineffective one.  And dogs are regarded differently in different cultures. In some cultures, they predominantly serve a protective function. In others, they are only semi domesticated but essentially unregulated (they don’t get rabies vaccine).

A safe and effective vaccine exists. You can either get a series of 3 intramuscular shots (days 0, 7, 21 or 28) as pre-exposure prophylaxis and then in the event of an exposure, you would need 2 additional vaccine injections (days 0 and 3). Or you can forego the pre-exposure prophylaxis and in the event of an exposure, you would need to get Rabies Immune Globulin (RIG) plus 4 shots of the vaccine over 14 days.

So…what are the factors that determine whether or not you should get the pre-exposure vaccine?

First off, let’s look at risk as defined as the likelihood of an event occurring plus the severity of the consequences of that event. For most of us who are not engaged in bat research, serious caving or veterinary medicine, the likelihood of an exposure is low. Clearly, the consequences of getting rabies are invariably fatal. However, if you do have an exposure, you can reliably prevent developing the disease by immediately beginning the full post exposure series of 4 shots of vaccine plus RIG.

Cost is not insignificant. The pre-exposure series is over $500. So…high cost, low risk and you’d still be able to reliably prevent the disease after the exposure without the pre-exposure vaccine? Seems like a no brainer. Skip the pre-exposure vaccine, right?

Not so fast. Some destinations have a higher likelihood of exposure than others. Most Middle Eastern countries, South East Asia, China, the Bahamas, parts of southern and western Africa, all have a high incidence of rabies. If you tend to stay in low-end accommodations and in more rural regions, you probably have a higher risk of exposure. And, if you are someone who can’t resist patting every dog and feeding every monkey, then you definitely have a higher risk of exposure.

And, not all vaccine is created equal. Modern cell culture vaccines are relatively safe. The 2 products licensed for use in the U.S. are Purified Chick Embryo Cell derived and Human Diploid Cell derived. There are other cell culture vaccines available overseas that would be equally effective and safe. However, rabies vaccine once was solely made from mammal brain tissue cultures. These are significantly less safe and still in use in many parts of the world, not coincidentally in many of the regions that have a high incidence of rabies. Additionally, RIG isn’t available everywhere either, “not coincidentally…etc”. If you’ve had the pre-exposure series, you don’t need RIG post exposure.

And, as with most hazards, it isn’t just about what country you are in, but where you are in the country. I was working in Bhutan last year. Bhutan has a very high per capita incidence of rabies (based on the very little epidemiological data available). Most hospitals and pharmacies get all their drugs from India once a year and the rabies vaccines are highly likely to be brain tissue derived. The nearest available RIG is in Bangkok. From where I was, it’s a 10-hour drive over a very winding, narrow road to get to the airport in Paro, assuming the roads are passable. Securing a plane reservation on one of the few regular commercial flights in and out is usually not a simple or fast process. It isn’t difficult to imagine a situation where the days would start to add up between an exposure and treatment with you finding yourself thinking a lot about that short end of the incubation period bell curve. Pre-exposure prophylaxis is thought to provide some protection in the event of a delay to post exposure treatment.

Another consideration is the post exposure treatment schedule. Should you need to travel to receive treatment, having had the pre-exposure prophylaxis means that you can return to your original destination after several days. Not having it means that you may not be able to return for a couple of weeks. If the mission that you are traveling for is important to you, this may make an enormous difference.

For most of us, it probably doesn’t add up. If you don’t travel that much or if your destinations are usually high income, etc. there are probably other uses for that $500 plus. However, if you travel frequently, especially to low and middle income countries, you might want to consider it.