Vaccination

Medicine helps your body stay strong.

A vaccine uses tiny, weak germs. These germs do not make you sick. They teach your body how to fight.

When many people get a vaccine, everyone stays safer. This helps people who cannot get them.

Long ago, a man named Edward Jenner helped. He made a vaccine for smallpox. Smallpox was a very bad sickness.

Vaccines help stop many diseases today. They keep us and our friends well.

Vaccines help your body fight sickness. They work by teaching your immune system. This is your body's way of staying safe from germs.

A vaccine uses tiny parts of a germ. These might be weak germs or small proteins. They do not make you sick. Instead, they prime your immune system. This means they prepare your body for the real germ later.

Many people use vaccines to stay well. When many people are vaccinated, it creates herd immunity. This means the germ cannot spread easily. It helps protect people who are too sick to get a vaccine.

Edward Jenner helped start this work. In 1796, he made a vaccine for smallpox. Smallpox was a very deadly disease.

Scientists test vaccines many times. They test them in labs and with animals first. Then, they use three phases of human trials. These trials check if the vaccine is safe and if it works.

Vaccination is a way to help the body stay healthy. It works by teaching your immune system to recognize and fight germs. A vaccine contains tiny pieces of a germ or a virus. These pieces might be weakened, killed, or just small proteins. They do not make a person sick like a real disease would. Instead, they act like a practice run for your body. This process is called immunization.

How does this teaching work? A vaccine uses something called an immunogen to start the process. This immunogen tells your immune system to wake up and pay attention. Your body then begins to build its own defenses. This can take several weeks to fully develop. Most vaccines are given as a small injection. However, some vaccines like the ones for polio are given orally. These go through the mouth to protect the bowel.

People have been trying to stop diseases for a long time. In the 16th century, people in China used a method called variolation. This used real smallpox germs to try to prevent the disease. Later, an English doctor named Edward Jenner changed everything. In 1796, he invented the smallpox vaccine. He was the first to show it worked through published evidence. Another scientist, Louis Pasteur, helped grow these ideas through microbiology.

Vaccines have saved a huge number of lives. Smallpox was a very deadly disease that killed many people. Because of vaccines, smallpox was finally gone in 1979. The World Health Organization says vaccines prevent 3.5 to 5 million deaths every year. One study found that vaccines prevented 154 million deaths between 1974 and 2024. This includes 146 million children under age five. Vaccines also helped eliminate polio and tetanus in many parts of the world.

Scientists are very careful when they make new vaccines. They test them in labs and with animals first. Then, they start three phases of human testing. Phase I tests safety with about 20 people. Phase II uses 50 to several hundred people. Phase III tests thousands of volunteers to see if it works well. Even after that, they use Phase IV to watch for many years. This keeps everyone safe as they use the medicine.

Vaccination is the process of administering a vaccine to help the immune system develop immunity. This process helps prevent sickness from an infectious disease by stimulating adaptive immunity. Vaccines work by introducing an immunogen, which is a substance that triggers an immune response. These immunogens can consist of a microorganism or virus in a weakened, live, or killed state. They may also contain specific proteins or toxins from the organism. By using these components, the body learns to recognize and fight the actual pathogen later.

The mechanism of vaccination involves priming the immune system. This artificial activation is known as immunization. Most vaccines are administered before a person contracts a disease to build future protection. However, some are given after exposure to reduce the severity of the illness. For example, vaccines given after smallpox exposure can offer some protection. Louis Pasteur famously provided the first rabies immunization to a child bitten by a rabid dog. This rabies vaccine is effective when administered several times over 14 days alongside wound care and immune globulin. While vaccination provides lasting protection, it usually takes several weeks to develop. This is different from passive immunity, such as breastfeeding, which has an immediate effect.

There are different ways to deliver these immunogens to the body. Most vaccines are given by injection because they are not absorbed reliably through the intestines. However, some vaccines, such as those for rotavirus, polio, and certain types of typhoid or cholera, are given orally. These oral vaccines work to produce immunity directly in the bowel. It is also important to distinguish vaccination from inoculation. Inoculation, or variolation, involves using unattenuated or unweakened pathogens. In the case of smallpox, variolation used material from a patient's pustule or scab. This method was often less effective and could cause the patient to become severely ill.

The history of immunization began long before modern medicine. The first recorded use of variolation occurred in China during the 16th century to prevent smallpox. Smallpox was a deadly disease that killed 20% to 60% of infected adults. It killed over 80% of infected children. In 1796, English physician Edward Jenner invented the smallpox vaccine. He was the first to publish evidence of its effectiveness and provide production advice. Later, Louis Pasteur furthered these concepts through his work in microbiology. The term "vaccination" itself comes from the virus used to affect cows.

Vaccination is one of the most successful public health achievements in history. The World Health Organization (WHO) states that vaccination prevents 3.5 to 5 million deaths every year. A study in The Lancet estimated that vaccination prevented 154 million deaths between 1974 and 2024. This total includes 146 million deaths among children under age five. Widespread immunity helped eradicate smallpox in 1979, a disease that killed 300 to 500 million people in the 20th century. Vaccination also helped eliminate polio and tetanus from much of the world. In the United States, the CDC named vaccination one of the ten great public health achievements of the 20th century.

To ensure safety, vaccines undergo a rigorous multi-stage testing process. Before human testing, researchers test vaccines on cell cultures and animal models like mice, rabbits, and monkeys. Once approved for human trials, they enter three distinct phases. Phase I tests safety in about 20 people. Phase II expands to 50 or several hundred people to evaluate dose and effectiveness. Phase III involves hundreds to thousands of volunteers to compare vaccinated groups to unvaccinated groups. Even after approval, Phase IV trials monitor safety in tens of thousands of people over many years. While minor side effects like fever are common, serious allergic reactions occur in about 1 out of 100,000 vaccinations.

Vaccines contain various ingredients to help them work effectively. Some use an adjuvant, such as aluminium salts, to create a stronger immune response. Aluminium hydroxide or aluminium phosphate have been used safely since the 1930s. Some vaccines also contained thimerosal, an organic compound containing ethylmercury. It is important to note that ethylmercury is different from the methylmercury found in contaminated fish. Although vaccination is highly effective, "vaccine failure" can occur. This happens when an organism contracts a disease despite being vaccinated. This is often due to individual variations in immune response rather than a defective vaccine.