Immunizations Explained

If you’ve ever looked over the list of recommended vaccines — DTaP, Hib, MMR — you might have felt like you were looking at the rough draft of an eye chart. Rest assured, there are some import medicines behind that jumble of letters. It’s worth knowing what those letters mean and what each vaccine can do. The more you know about vaccines, the more likely you’ll be to keep yourself and your children up-to-date on every shot.

DTaP vaccine

Protects against these three diseases:

Diphtheria, caused by Corynebacterium diphtheriae

The bacterium that causes this disease is spread by coughing, sneezing, and touch. It causes sore throats, fever and sometimes heart failure or paralysis. Before the vaccine was developed in the 1930s, diphtheria was one of the most common causes of death among children. According to the Centers for Disease Control and Prevention (CDC), diphtheria would kill up to 10 to 20 percent of those infected if people in the U.S. stopped getting immunized. Outbreaks are still occurring overseas where the death rate is much higher.

Tetanus, caused by Clostridium tetani

A bacterium lurking in soil causes this disease, most commonly by entering the bloodstream through a wound. It attacks nerves that control muscles, causing muscle stiffness, spasms, and difficulty in opening the mouth (hence the common name, “lockjaw”). Over 10 percent of those with tetanus die.

Pertussis, caused by Bordetella pertussis

This disease is known as whooping cough because of the violent coughing it causes. The cough is also what spreads the bacterium. Symptoms last for up to 10 weeks and can result in pneumonia, seizures, brain damage, and death. One in 200 infected with it die. Before the vaccine was developed in the 1950s, pertussis killed more U.S. children than all other infectious diseases combined. This disease still continues to pose a real threat in the United States. Adults whose immunity has waned can infect people who have either not been immunized or haven’t completed the full series of shots. Researchers have developed an “acellular” form of this vaccine (DTaP), which is in widespread use and is associated with far fewer side effects than the older DPT vaccine.

Hepatitis A vaccine

Protects against: Hepatitis A, caused by the hepatitis A virus

Hepatitis A spreads when virus from an infected person’s feces somehow gets into food or water. About 14 to 40 percent of cases in the U.S. occur in children at daycare centers because of contact with diapers. It infects the liver, and symptoms include fatigue, nausea, lack of appetite, fever, and aching. When the liver gets inflamed, the bile turns the skin and whites of the eyes yellow. It’s generally not severe, and unlike hepatitis B, it isn’t a chronic condition.

Hepatitis B vaccine

Protects against: Hepatitis B, caused by the hepatitis B virus

Like the AIDS virus, the virus for hepatitis B spreads through bodily fluids. It infects the liver. About 90 percent of people over age 5 who are infected will have an acute form of the disease, which tends to last 1 to 3 months. Symptoms of acute hepatitis B may include nausea, jaundice, pain, chronic fatigue, and dark urine. The other 10 percent of those infected over age 5 will become chronic carriers, who may not have any symptoms for years, but who are at risk of developing serious liver conditions, such as cirrhosis or liver cancer. Among infants, however, those statistics are reversed. About 90 percent of infants who are infected will develop chronic hepatitis.

Hib vaccine

Protects against: H. influenzae type b infections, caused by Haemophilus influenzae type b

Despite its name, this bacterium doesn’t cause the flu, but it does cause invasive, life-threatening disease: blood infection, epiglottitis (an infection in the airways that can obstruct breathing), and meningitis (inflammation of the membranes covering the brain and spinal cord). This can lead to brain damage and death. Before the introduction of the vaccine in 1987, it was the most common cause of bacterial meningitis in the U.S., killing more than 600 children per year.

Human Papillomavirus (HPV) vaccine

Protects against: Human papillomavirus infections, caused by human papillomavirus

There are more than a hundred different types of HPV, and 40 of these can be transmitted sexually. At least 50 percent of sexually active men and women get the disease. Most of the time, an infected person will notice no symptoms and the virus will clear up on its own. For others, it can lead to life-threatening or chronic disease. HPV is responsible for up to 70 percent of cervical cancers and 90 percent of genital warts. In 2006, the U.S. Food and Drug Administration approved its first HPV vaccine. In February 2007, the CDC added it to its immunization schedule and recommended it for all females aged 11 to 12 years old (though girls as young as 9 can get it). For girls and women aged 13 to 26 years old who haven’t been immunized, the CDC recommends a catch-up vaccination.

MMR vaccine

Protects against these three diseases:

Measles (rubeola), caused by the measles virus

Spread by sneezing, the measles virus causes cold-like symptoms, then fever, inflamed eyes, and a red rash. In rare cases, it can lead to pneumonia and encephalitis (brain inflammation), which can result in death. In 2008 there were 164,000 deaths worldwide; outbreaks still occur in the United States.

Mumps, caused by the mumps virus

An airborne virus causes swelling of the salivary glands on either side of the mouth. Rarely life-threatening, mumps can be painful, especially in teenage and adult males who may experience an inflammation of the testes.

Rubella, caused by the rubella virus

Also known as German measles, this virus is spread through the air. It causes a rash, enlarged lymph nodes, and sometimes a slight fever. Most victims experience only mild symptoms, but up to 90 percent of women who get infected in the first trimester of pregnancy will have a baby affected with congenital rubella syndrome (heart defects, mental retardation, and cataracts).

Pneumococcal conjugate (PCV)

Protects against: Streptococcus pneumoniae (pneumococcus), a group of bacteria that causes pneumonia, meningitis, bacteremia (blood infection), sinusitis and middle ear infections.

According to the CDC, pneumococcal disease causes about 4,800 deaths each year. Adults over age 65, children under age 2, and people with underlying medical conditions or weak immune systems are especially high risk. Pneumococcus is spread mostly through respiratory droplets from the nose or mouth. Symptoms vary depending on the form of the disease, but often include a fever and chills.

Polio vaccine (OPV or IPV)

Protects against: Poliomyelitis, caused by poliovirus

Commonly known as polio, the disease spreads mostly through exposure to feces. Most infected children suffer only a mild illness, but sometimes the disease causes acute paralysis that can lead to permanent disability and even death.

Since the oral polio vaccine (OPV) was found to cause polio in a very small percentage of people (about one in 2.4 million), it’s no longer used in the United States. The “killed” virus in the inactivated polio vaccine (IPV) is slightly less powerful than the oral vaccine: It can’t cause the disease but it also doesn’t provide immunity in the intestinal tract. Experts feel comfortable recommending IPV because polio has been eradicated from the United States and is less common abroad than it used to be. The oral vaccine is still used in many other countries, however, and may be recommended in cases of polio outbreaks or within four weeks of travel to an area where polio is prevalent. If someone in the household or a caretaker has AIDS or cancer, or is taking medication that suppresses the immune system, only the IPV should be used.

Rotavirus (Rota) vaccine

Protects against: Rotavirus, caused by rotaviruses

By age 3, a majority of children not immunized against this virus have been infected with it. The most common symptom is diarrhea, which sometimes results in dehydration so severe that the child must be hospitalized. Where modern hospitals are not available, many children die. A vaccine was approved by the FDA in 1998 but suspended in July 1999 due to possible risks of a serious intestinal disorder. However in February 2006, the CDC’s Advisory Committee on Immunization Practices recommended a newly designed rotavirus vaccine for infants after reviewing results from a study involving 70,000 children. The CDC adopted the new rotavirus vaccine into its immunization schedule in February 2007.

Varicella (Var) vaccine

Protects against: Varicella, caused by varicella zoster virus

Commonly called chicken pox, this disease is spread by an airborne virus. It causes fever and a rash of small, red, itchy blisters. Severe cases (which do not usually affect young children) can result in liver, kidney, and brain problems. Adults occasionally suffer life-threatening pneumonia. The vaccine, approved by the FDA in 1995, provides complete protection for 80 to 90 percent of those vaccinated. Those who are vaccinated and get the disease are likely to have milder symptoms than those who are not vaccinated.


Centers for Disease Control and Prevention. Immunization schedules. 2010.

World Health Organization. Measles. 2009.

Centers for Disease Control. What Would Happen If We Stopped Vaccinations? May 2007.

Centers for Disease Control. Genital HPV Infection — CDC Fact Sheet. March 2008.

National Cancer Institute. Human Papillomaviruses and Cancer: Questions and Answers. February 2008.

World Health Organization. Measles. November 2007.

American Academy of Family Physicians. Pneumococcal Conjugate Vaccine: What A Parent Needs to Know. November 2006. http:

Centers for Disease Control. Polio Vaccination. May 7, 2009.

Centers for Disease Control. Varicella (Chickenpox) Vaccination. April 8, 2008.

Centers for Disease Control. Tetanus Disease In Short (Lockjaw). May 2009.

Centers for Disease Control. Pink Book: Epidemiology and Prevention of Vaccine Preventable Diseases. 11th Edition. May 2009.

© HealthDay

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