The story of Chip and Dale

To understand how vaccines work you need to understand the story of two 5-year-old children, Chip and Dale.

Chip

Chip plays with a child in his class who has measles. Ten days later, Chip develops high fever, runny nose, "pink eye” and a rash. The rash consists of red bumps that start on his face and work their way down to the rest of his body. After two more days, Chip starts to have trouble breathing. His breaths are short and rapid. Chip's mother takes him to the doctor where he gets an X-ray of his chest. The X-ray shows that Chip has pneumonia (a common complication of measles infection). Chip is admitted to the hospital where he stays for five days and finally recovers. After having fought off his measles infection, Chip will never get measles again. Or, said another way, Chip has immunity to measles. Chip is immune to measles because he has cells in his body that recognize and can make "antibodies" to measles virus. These cells, called "memory B cells,” developed during the infection and will hang around for the rest of Chip's life.

Dale

Dale also plays with the child who has measles. However, Dale never develops symptoms of measles. He doesn't get fever, rash or pneumonia. Dale was infected with measles virus, but he didn't get any of the symptoms of measles. This is called an "asymptomatic infection.” Because Dale, like Chip, also develops “memory B cells,” he is also immune to measles for the rest of his life.

The difference between Chip and Dale

Whereas Chip had to pay a high price for his immunity, Dale didn't. Dale was lucky. Although some children don't get severe infections when they are exposed to measles, most do. Before a measles vaccine was developed in 1963, measles would infect about 3-4 million children each year in the United States, causing about 48,000 children to be hospitalized, about 1,000 to suffer encephalitis (swelling of the brain), and about 400-500 to die.

Vaccines take the luck out of it

By also causing "asymptomatic infections,” vaccines mimic what happened to Dale. This allows children to benefit from the natural immunity that comes with infection without having to suffer the severe, and occasionally fatal, consequences of natural infection.

Vaccines remove the element of luck by controlling:

• The dose of the exposure (smallest amount needed)
• The timing of exposure (before the period of highest risk)
• The potential severity of the pathogen

Watch a video about how the pertussis vaccine works in a community.

Learn how vaccines are made, so they cause immunity without causing disease.

Learn more about the immune system.

Is natural infection better than immunization?

It is true that natural infection almost always causes better immunity than vaccines. Whereas immunity from disease often follows a single natural infection, immunity from vaccines usually occurs only after several doses. However, the difference between vaccination and natural infection is the price paid for immunity.

The price paid for immunity after natural infection might be pneumonia from chickenpox (varicella), mental delay from Haemophilus influenzae type b (Hib), pneumonia from pneumococcus, birth defects from rubella, liver cancer from hepatitis B virus, or death from measles.

Immunization with vaccines, like natural infections, induces immunity, but unlike natural infection, immunization does not exact such a high price for immunity.

If you could see the world from the perspective of your immune system, you would realize that where the virus or bacteria comes from is irrelevant. Your immune system “sees” something that is foreign, attacks it, disables it and then adds information about the pathogen to its memory bank. The next time the pathogen is encountered, your immune system is prepared to react more quickly.

The differences between a vaccine and getting the disease naturally are the dose, the known time of exposure, and the potential severity of the pathogen.

• Dose - When someone is exposed to viruses or bacteria naturally, the dose is often larger, so the immune response that develops will typically be greater (as will the symptoms). However, when scientists are designing vaccines, they determine the smallest amount of virus or bacteria needed to generate a protective immunologic response.
• Time of exposure – Most of the time, we do not know when we are exposed to viruses and bacteria; however, when we get a vaccine, we do know. In essence, we are controlling our own (or our child’s) exposure to the viruses or bacteria that the vaccines protect against because we know when and where they occur. In contrast, and more typical of the norm, we don’t know what viruses or bacteria we are exposed to from the doorknob to the doctor's office, the pen at the sign-in desk, the books in the waiting room, or the other patrons at the restaurant we go to after the office visit.
• Potential severity of the pathogen – When someone gets sick from exposure to a pathogen in the community, called natural infection, they can experience mild illness or become very sick or even die. On the other hand, vaccination provides immunity without having to suffer the severe, and occasionally fatal, consequences of natural infection.

Of interest, a few vaccines induce a better immune response than natural infection:

• Human papillomavirus (HPV) vaccine −The high purity of the specific protein in the vaccine leads to a better immune response than natural infection.
• Tetanus vaccine − The toxin made by tetanus is so potent that the amount that causes disease is actually lower than the amount that induces a long-lasting immune response. This is why people with tetanus disease are still recommended to get the vaccine.
• Haemophilus influenzae type b (Hib) vaccine − Children younger than 2 years of age do not typically make a good response to the complex sugar coating (polysaccharide) on the surface of Hib that causes disease; however, the vaccine links this polysaccharide to a helper protein that creates a better immune response than would occur naturally. Therefore, children younger than 2 years of age who get Hib disease are still recommended to get the Hib vaccine.
• Pneumococcal vaccine − This vaccine works the same way as the Hib vaccine to create a better immune response than natural infection in young children.

So, in summary, a vaccine affords us protection with lesser quantities of virus or bacteria, the control of scheduling the exposure, and the knowledge that immunity will be gained without experiencing severe illness.

Watch as Dr. Offit talks about natural infection and vaccination in the short video below, part of the Talking About Vaccines with Dr. Paul Offit series.

Is there a difference between vaccination and immunization?

Although we commonly use the words vaccination and immunization interchangeably, they are not exactly the same.

Vaccination was first coined as a term when Edward Jenner used cowpox to immunize people against smallpox. The word vaccination comes from the Latin word vaccinae meaning “of the cow.”

Immunization means immunity induced by a biological agent. The word immunization comes from the Latin word immunes, referring to “a group of soldiers who once having fought and survived a battle never had to fight again.” In our society, immunity has come to mean freedom from anything burdensome; in the case of vaccines, our children are the soldiers; the vaccines are the battle, and the freedom gained is from disease.

There are two forms of immunization:

1. Active immunization means administering a vaccine, so that the recipient generates their own immune response. Receipt of hepatitis B vaccine is an example of active immunization.
2. Passive immunization means administering antibodies or antitoxins from another source to protect the recipient. Antibodies passed from mother to child through breast milk are an example of passive immunization.

Find out more about active and passive immunity as well as a third type, called “community immunity” or “herd immunity.”

Vaccines and antibiotics

Vaccines and antibiotics are two of the most powerful tools against bacterial infections. Vaccines work by preventing infections, whereas antibiotics work by treating them. 

About antibiotics

Antibiotics were first discovered in the early 1900s when a drug called sulfanilamide was found to protect people from fatal bacterial infections such as pneumococcus. Pneumococcus causes pneumonia, bloodstream infections and meningitis.

Perhaps the most well-known antibiotic is penicillin. By the 1940s penicillin could be produced in large quantities and was recognized as an easy way to save people from disease and death caused by pneumococcus. Doctors believed that they could eliminate pneumococcus with these new tools; thus interest in learning more about preventing pneumococcus by vaccine waned.

Dr. Robert Austrian was a physician who continued studying pneumococcal infections, first in New York and later throughout the country. His studies showed that while people treated with penicillin were less likely to die from their infections, pneumococcus was still infecting as many people as it did before penicillin was available. He also found that people who got the most severe infections with pneumococcus died regardless of whether or not they were treated with antibiotics. The only way to protect them would be to prevent their infections in the first place; that is, to immunize them.

While Dr. Austrian was completing his studies, people were continuing to be infected and treated for pneumococcal infections using antibiotics, such as penicillin. Antibiotics resolve infections by stopping the bacteria from reproducing themselves.

However, bacteria respond in a "survival of the fittest" manner. These antibiotic-resistant bacteria continue to reproduce and can be passed on to others.

Antibiotic resistance was discovered shortly after penicillin came into popular use. By 1967, pneumococcal strains resistant to penicillin began to appear. At first, the answer to antibiotic resistance was simple. If the bacteria resisted penicillin, use another antibiotic. However, by the 1980s and 1990s, as pneumococcus and other bacteria became more resistant to antibiotics, doctors were running out of options. Indeed, today there are strains of bacteria for which no existing antibiotic will work. Although scientists continue to research, design and test new antibiotics, the process is slow and expensive.

In the case of pneumococcus, we have had some reprieve — Dr. Austrian's first vaccine became available in the late 1970s and a second version, still used for adults today, was introduced in 1983. Although Dr. Austrian's vaccine worked in adults, it did not work well in young children. In 2000 another version, called pneumococcal conjugate vaccine, that works better in children also became available; since then, these vaccines have been enhanced to protect against more types of pneumococcus and they have also been used to better protect adults. As more people in the community are immunized against a particular type of bacteria, such as pneumococcus, there are fewer opportunities for the bacteria to reproduce and infect others. Thus, vaccines have become one of our most important tools in the fight against antibiotic resistance.

To stem resistance, in addition to getting vaccines, people should:

• Only use antibiotics when ill with a bacterial infection. Antibiotics are not effective against colds or flu caused by viruses. Overuse of antibiotics can lead to increasingly resistant bacteria that can cause untreatable infections in that person or be passed on to others.
• Do not use old antibiotics or those prescribed for others, as they may not be as effective at treating your current infection; the drugs may allow the bacteria to continue replicating and spreading to others.

An important difference between vaccines and antibiotics

One important difference between vaccines and antibiotics is how they work. Whereas antibiotics spread throughout the body to stop an infection, vaccines are processed near the site where they are given, such as in a muscle in the arm. After a vaccine is processed, the immune cells generated in response to the vaccine circulate through the body. As a result, dosing for antibiotics and vaccines is different. Whereas doses of antibiotics need to account for the size of a person’s body, vaccines do not. Instead, doses need to account for the ability of the immune system to respond. Find out more about dosing considerations.