Vaccination for Rare Diseases
The recommended immunization schedule for children in the United States includes vaccinations to protect against 15 different diseases by age six:
- Hepatitis B (a virus that affects the liver)
- Rotavirus (a virus that can cause severe diarrhea in infants and children)
- Diphtheria, Tetanus and Pertussis (combined shot—DTaP)
- Haemophilus influenzae type b (“Hib”—bacterium that can cause pneumonia, bacterial meningitis and other infections)
- Pneumococcal (protects against Streptococcus pneumonia, a bacterium that causes many types of pneumococcal infection including pneumonia, meningitis, and sepsis)
- Inactivated Poliovirus
- Measles, Mumps, Rubella (combined shot—MMR)
- Varicella (chickenpox)
- Hepatitis A (a virus that affects the liver)
- Meningococcal (protects against Meningococcus, a bacterium that causes meningitis and other infections)
For a few of the diseases listed, some people question whether vaccination is really necessary given the currently low rates of illness. Polio, for example, was eliminated from the Americas in 1994; why, then, should American children be given a poliovirus vaccine? Similarly, measles was declared eliminated from the United States in 2000; so why vaccinate against measles?
The answer is fairly simple: thanks to widespread vaccination and surveillance campaigns, polio and measles are now “rare” diseases in the United States—but they are still circulating in other regions. Widespread vaccination generally protects us from outbreaks even when an infected traveler enters the country, but if we stopped vaccinations, one imported case of measles (to choose an example) could spread through the unprotected population like wildfire.
Recent history is rife with warning signs: an unvaccinated seven-year-old boy from California exposed 839 people to the measles when he brought it back with him after a trip to Europe in 2008. Eleven unvaccinated children in the San Diego area caught the disease, one a baby that required three days of hospitalization. The outbreak cost nearly $180,000 to control, from personnel and medical costs to the cost of quarantine efforts, and led health officials to remind the public that measles is only a “plane ride away.”
The Centers for Disease Control and Prevention’s Morbidity and Mortality Weekly Report for August 22, 2008 addressed a nationwide increase in measles cases reported to the CDC in 2008. The MMWR noted that in the years between the declaration of measles elimination in the United States (in 2000) and 2007, the country averaged 63 cases annually. However, by the end of July 2008, 131 cases had already been reported to the CDC for the year. The report goes on to analyze the reported cases and underscore the importance of high vaccination coverage:
Among those measles cases reported during the first 7 months of 2008, 76% were in persons aged <20 years, and 91% were in persons who were unvaccinated or of unknown vaccination status. Of the 131 cases, 89% were imported from or associated with importations from other countries, particularly countries in Europe, where several outbreaks are ongoing. The findings demonstrate that measles outbreaks can occur in communities with a high number of unvaccinated persons and that maintaining high overall measles, mumps, and rubella (MMR) vaccination coverage rates in the United States is needed to continue to limit the spread of measles…
Measles is one of the first diseases to reappear when vaccination coverage rates fall. Ongoing outbreaks are occurring in European countries where rates of vaccination coverage are lower than those in the United States, including Austria, Italy, and Switzerland... In June 2008, the United Kingdom's Health Protection Agency declared that, because of a drop in vaccination coverage levels (to 80%--85% among children aged 2 years), measles was again endemic in the United Kingdom, 14 years after it had been eliminated. – Morbidity and Mortality Weekly Report (CDC), August 22, 2008
In short, we vaccinate for many rare and “disappeared” diseases because we want them to stay that way.
Vaccination for Travel: Other Rare Diseases
Vaccination for certain other diseases considered rare or “disappeared” in the United States is only recommended if you are traveling to an area of the world in which that disease is widespread. The U.S. immunization schedule, for example, does not recommend routine vaccination for yellow fever; however, if you are traveling to areas of the world where the disease remains endemic, you may be recommended—or even required—to get the vaccine. Travel to certain countries in South America and sub-Saharan Africa requires a yellow fever vaccination.
The vaccination recommendations for yellow fever—a virus spread by the bite of infected mosquitoes—differ from those for other “rare” (in the United States) diseases like polio and measles primarily because of the difference in how they spread. Measles and polio can spread directly from one human being to another; a single infected traveler entering or returning to the U.S. could expose everyone he or she came in contact with to the disease. Yellow fever, however, cannot be spread directly between humans. The virus can only be transmitted by the bite of a particular type of mosquito that’s been infected—and then only if the mosquito fed off an infected host a certain period of time before biting its latest victim. Therefore, yellow fever can spread relatively easily in areas with both large mosquito populations and a large number of infected humans on which the mosquitoes can feed, but not in areas without them. In the United States, the last yellow fever outbreak was in New Orleans in 1905. Two fatal cases were reported in the 1990s, both in U.S. residents returning from trips to South America. Neither had been vaccinated.
The Centers for Disease Control and Prevention website offers information about vaccinations for travelers. You can find more information here.
Timeline Entry: 1893 Low Vaccination Rates Lead to Outbreak
A Muncie, Indiana, smallpox outbreak illustrated the effect of lower vaccination rates on the spread of disease. A local physician noted that vaccination there had been largely neglected since the last epidemic of smallpox in 1876.
The initial cases appeared in a family in which only one member had been vaccinated. Physicians were unsure whether the disease was smallpox or chickenpox, and established a quarantine too late to control disease spread.
Despite measures that included a near-quarantine of the city, fumigation of mail, cancellation of public gatherings, and compulsory vaccination, the epidemic spread from May 1893 through October. In the end, 140 people contracted smallpox and 20 died of it. Approximately 13,000 people were vaccinated during the epidemic, with one possible death resulting from post-vaccination tetanus infection.
The careful collection of epidemic-related data shown in the images points to the emerging use of statistics to analyze disease spread. This tendency will grow through the 20th century.See This Item In The Timeline