Vaccine

A vaccine is a biological preparation that helps people stay safe from certain diseases. It works by giving the body a tiny, harmless piece of a germ. This could be a weakened or dead part of the germ. This piece teaches the immune system to recognize and fight the real germ if it ever tries to make someone sick.

Vaccines can stop diseases before they start, or help fight diseases that have already begun. Because of vaccines, many dangerous diseases like smallpox, polio, and measles are rare in many parts of the world today.

The idea of giving people a way to prevent disease by putting a little bit of the germ in their body has been around for hundreds of years. One of the earliest examples was in China, where people used a method called inoculation to protect against smallpox. Later, a man named Edward Jenner discovered that a disease called cowpox could protect people from smallpox. He is often called the father of vaccines.

Today, the World Health Organization says there are vaccines for twenty-five different diseases that can be prevented. Because of these vaccines, millions of people stay healthy every year.

Effectiveness

Scientists agree that vaccines are safe and effective tools for fighting infectious diseases. When we get a vaccine, our immune system practices fighting a germ without getting sick. This way, if the real germ tries to infect us later, our body is ready to stop it.

Because of vaccines, diseases like smallpox have been wiped out, and others like polio, measles, and chickenpox are much less common. Vaccines help protect entire communities by making it harder for diseases to spread widely, known as herd immunity.

However, vaccines aren’t perfect. Sometimes a person’s body might not respond as well, especially if they are older or have a weaker immune system. The protection might not last forever. Still, even when vaccines don’t prevent infection completely, they usually make the illness milder and less dangerous.

Safety

Main article: Adverse vaccine event

Vaccines are very safe for children, adolescents, and adults. Most side effects are mild and may include a fever, soreness where the shot was given, or muscle aches. Some people might be allergic to ingredients in the vaccine. Severe side effects are very rare.

Certain factors like age, health status, and allergies can affect how well a vaccine works. Older adults and people with certain health conditions might need special vaccines or extra doses to stay protected. Some vaccines have very rare complications, but these are extremely uncommon. Some countries have programs to help people who experience serious side effects from vaccines.

Types

Vaccines help protect people from getting sick by teaching their bodies to recognize and fight off harmful germs. They usually contain parts of these germs that have been weakened or changed so they can't cause illness.

There are several types of vaccines. Some use live, weakened germs that still can trigger an immune response. Others use germs that have been killed or parts of them to train the immune system. Modern vaccines also include those made from genetic material, which help cells produce pieces of the germ to trigger immunity. Each type has its own benefits and is used to protect against different diseases.

Main article: Attenuated vaccine

Main article: Inactivated vaccine

Main article: Toxoid

Main article: Subunit vaccine

Main article: Conjugate vaccine

Main article: Heterologous vaccine

Main article: Genetic vaccine

Main article: Viral vector vaccine

Main article: RNA vaccine

Main article: DNA vaccine

Valence

Vaccines can protect us from one or many diseases.

A monovalent vaccine, also called univalent, works against just one germ or part of a germ.

A multivalent vaccine, also called polyvalent, can protect against two or more strains of the same germ, or even different germs. Doctors sometimes use special names like bivalent, trivalent, or tetravalent to show how many strains a vaccine can fight.

When two or more vaccines are mixed together, they can sometimes get in each other’s way. This is especially true with certain types of vaccines made from live, weakened germs. For example, in the old polio vaccine, one part was strong enough to block the others, so scientists had to adjust the amounts to make sure all parts worked well. Similar issues were seen with some dengue vaccines, where one strain was too strong and stopped the others from working properly.

Other contents

Adjuvants

Main article: Immunologic adjuvant

Vaccines sometimes have substances called adjuvants. These help the body’s immune system work better. For example, the vaccine for tetanus may use a substance called alum to make it more effective.

Preservatives

Some vaccines have preservatives. These keep the vaccines safe from harmful bacteria or fungi. A preservative called thiomersal was used in the past, but it is now rarely used in childhood vaccines because it contains mercury. Research shows that vaccines do not cause autism.

Excipients

Besides the main part of the vaccine, vaccines may contain other ingredients such as:

• Aluminum salts to help the vaccine work better
• Antibiotics to stop bacterial growth during production
• Egg protein in some vaccines like the influenza vaccine because they are made using chicken eggs
• Formaldehyde to safely prepare certain vaccines
• Stabilizers like monosodium glutamate (MSG) to keep the vaccine effective
• Thiomersal in some vaccines to prevent contamination, though it is used in very small amounts today

Nomenclature

Different places use different short ways to name vaccines. In the United States, vaccines like DTaP protect against three diseases. Big letters mean full-strength doses. Small letters mean smaller doses for older kids and adults.

The Centers for Disease Control and Prevention keeps a list of these short names. You can also find these names on the CDC’s page called "Vaccine Acronyms and Abbreviations". In the United States Adopted Name system, the name of a vaccine puts the main thing first, like "poliovirus vaccine live oral" for OPV.

Licensing

See also: Vaccine trial

A vaccine gets special approval, called licensing, after many tests show it is safe and works well to stop diseases. These tests happen in stages and check that the vaccine prevents infections.

The World Health Organization helps countries set rules for making and checking vaccines. Each country then gives its own approval before using the vaccine. After a vaccine is approved, it may be in short supply at first, so plans are made to decide who should get it first. Countries work together to make sure vaccines are made safely.

Scheduling

Main article: Vaccination schedule

For country-specific information on vaccination policies and practices, see Vaccination policy.

Children get vaccinations when their bodies are ready to fight diseases. This creates schedules for when vaccines should be given. Guidelines are made by the Strategic Advisory Group of Experts and changed for each country by local advisory committee. In the United States, the Advisory Committee on Immunization Practices suggests vaccines for children to protect against diseases like hepatitis A, hepatitis B, polio, mumps, measles, rubella, diphtheria, pertussis, tetanus, HiB, chickenpox, rotavirus, influenza, meningococcal disease, and pneumonia.

With many vaccines and booster shots suggested (up to 24 shots by age two), it’s important to keep track. To help with this, combination vaccines like the Pentavalent vaccine and MMRV vaccine are used, protecting against several diseases in one shot. Vaccines are also recommended at different ages, with extra doses for measles, tetanus, influenza, and pneumonia. Pregnant women are checked for rubella protection, and the human papillomavirus vaccine is advised in the U.S. and UK. Older adults are encouraged to get vaccines for pneumonia, influenza, and shingles, a rash caused by the chickenpox virus.

Economics of development

Main article: Economics of vaccines

Making vaccines can be hard because some serious diseases, like HIV, malaria, and tuberculosis, are most common in countries that don’t have many resources. In places like the United States, it can be tough to make money from vaccines, and there are risks.

Most vaccines have been made with help from governments, schools, and groups that don’t try to make a profit. These vaccines have saved many lives and helped public health. More vaccines are given to children now, partly because some governments require certain vaccines before a child can start school.

Patents

The World Health Organization says that the biggest problem for making vaccines in poorer countries isn’t usually patents. It’s more about needing money, good facilities, and trained workers. Unlike some medicines, each vaccine made in a new place must be tested again to be sure it’s safe. Some vaccines, like the human papillomavirus vaccine, have patents that can make them harder to produce in other places. During the COVID-19 pandemic in 2021, world leaders talked about changing intellectual property rules to help make more COVID-19 vaccines available faster.

Production

Making vaccines is different from making other medicines because vaccines are given to healthy people. This means the process must be very careful and follow strict rules.

There are many steps to make a vaccine. First, a part of the germ that helps the body fight sickness, called an antigen, is made. This can be done using chicken eggs, human cell cultures, or special machines called bioreactors. After the antigen is made, it is cleaned and prepared, sometimes with extra ingredients to help the body respond better. The last step is putting the vaccine into small bottles to use. New ways, like using special cell cultures, are being made to improve vaccine production.

Delivery systems

One of the most common ways to give vaccines to people is by injection. Researchers are looking for new ways to give vaccines that are safer and easier, like using liposomes and ISCOM (immune stimulating complex).

Oral vaccines, taken by mouth, have been very helpful. For example, an oral polio vaccine worked well even when given by volunteers without special training. Oral vaccines have good points, like no risk of blood issues and they do not need to stay very cold when moved, which can save money. Other new ideas include microneedle patches and dermal patches, which are still being tested and could make giving vaccines easier.

In veterinary medicine

See also: Influenza vaccine § Veterinary use, and Vaccination of dogs

Vaccines help protect animals from diseases. They stop animals from spreading diseases to humans. Both pets and farm animals get vaccines regularly. Sometimes, wild animals get vaccines too, like food with vaccines to help control rabies in raccoons.

In areas where rabies happens, vaccinating dogs is often required by law. Dogs can get vaccines for diseases like canine distemper, canine parvovirus, and Lyme disease.

DIVA vaccines

DIVA vaccines can tell if an animal is infected with a disease or just vaccinated. These vaccines are missing a part that the real disease has. A special test can show if an animal has the vaccine or the disease. This has helped countries remove some diseases from pigs and cattle. Scientists are trying to use this idea for more animal diseases.

History

Further information: Vaccination § History, and Inoculation § Origins

Long ago, people found ways to protect themselves from diseases like smallpox. One old method was called variolation. This involved putting a tiny amount of smallpox material into the nose or skin. It helped the body learn to fight the disease without getting very sick. Records show this practice in China as far back as the 15th century.

The story of vaccines began in 1796 when a doctor named Edward Jenner used material from cowpox—a harmless disease for humans—to protect a young boy from smallpox. This was the first true vaccine. Later, scientists like Louis Pasteur made vaccines for other diseases. They used weakened or parts of germs to teach the body to fight back. Over time, vaccines have helped control and even stop diseases like smallpox, making our world safer.

Trends

Since 2013, scientists have been working on new kinds of vaccines. They are studying the outer parts of a virus to make vaccines better.

Researchers are also looking at how the body’s defenses can help make vaccines for diseases not caused by germs, like some kinds of cancer. For example, a test vaccine called CYT006-AngQb was studied to see if it might help with high blood pressure. Many things affect how vaccines are made, such as new medical discoveries, changes in society, and health rules.

Plants as bioreactors for vaccine production

In 2003, scientists started testing plants to make vaccines. By adding special genes, plants like tobacco, potato, tomato, and banana can produce substances that work like vaccines. By 2005, bananas were made that could create a vaccine for hepatitis B.

Vaccine hesitancy

Main article: Anti-vaccine activism

Vaccine hesitancy means choosing to delay or skip vaccines even when they are offered. This might mean not getting a vaccine at all, waiting a long time to get it, or only getting some but not all needed vaccines. Even though experts agree vaccines are safe and helpful, when people hesitate, more people can get sick from diseases that vaccines can prevent. Because of this, the World Health Organization said in 2019 that vaccine hesitancy was a major danger to health around the world.

When many people do not get vaccines, diseases that used to be rare can return and spread, causing outbreaks and serious health problems from vaccine-preventable diseases. This is why it is important for everyone to know how much vaccines help keep us healthy.