Vaccine

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

Vaccines can be used to stop diseases before they start, or to 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

There is strong agreement among scientists that vaccines are safe and effective tools for fighting and stopping infectious diseases. When we get a vaccine, our immune system practices recognizing and fighting a germ without actually 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 completely wiped out, and others like polio, measles, and chickenpox are much less common. For example, before a measles vaccine, there were hundreds of thousands of cases in the United States each year. After the vaccine, cases dropped to just a few each year. Vaccines help protect entire communities by making it harder for diseases to spread widely, known as herd immunity. They also reduce the chance that germs will become resistant to medicines.

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. Also, the protection might not last forever, or it might only reduce how sick someone gets if they do get the disease. 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 generally safe for children, adolescents, and adults. Most side effects are mild and may include 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, like proteins or sugars, to train the immune system. Modern vaccines also include those made from genetic material, such as RNA or DNA, 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 be designed to protect against 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. Sometimes, doctors 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 often include substances called adjuvants to help the body’s immune system respond more strongly. For example, the vaccine for tetanus is sometimes combined with a substance called alum to make it work better. In special situations, like during the 1990 Persian Gulf campaign, one vaccine was used to help another vaccine work faster.

Preservatives

Some vaccines contain preservatives to keep them safe from harmful bacteria or fungi. A preservative called thiomersal was used in many vaccines in the past, but it is now rarely used in childhood vaccines because it contains mercury. Studies have shown that vaccines, including the MMR vaccine, do not cause autism.

Excipients

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

• Aluminum salts to help the vaccine work better
• Antibiotics to prevent 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, but some common ones are used around the world. For example, in the United States, vaccines like DTaP stand for a mix that protects against diphtheria, tetanus, and pertussis. Big letters like “D” and “T” mean full-strength doses, while small letters like “d” mean smaller doses used for older kids and adults.

The Centers for Disease Control and Prevention keeps a list of these short names to help everyone understand vaccine labels better. Another place to find these names is 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 calling it "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 called Phases I–III and include checking that the vaccine prevents infections and stays effective over time. Because vaccines are given to healthy people, they must meet very high safety standards.

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 and to watch for any problems after people get vaccinated.

Scheduling

Main article: Vaccination schedule

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

Children receive vaccinations when their immune systems are ready to respond, with extra "booster" shots to keep protection strong. This creates detailed vaccination schedules. Global guidelines are provided by the Strategic Advisory Group of Experts and adapted for each country by local advisory committee, considering local disease patterns and resources. In the United States, the Advisory Committee on Immunization Practices suggests vaccines for children 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 boosters 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 painful rash caused by the chickenpox virus.

Economics of development

Main article: Economics of vaccines

Creating vaccines can be challenging because many serious diseases, like HIV, malaria, and tuberculosis, are most common in countries with fewer resources. In places like the United States, making money from vaccines is often difficult, and there are many risks.

Most vaccines have been developed with help from governments, schools, and groups that don’t aim to make a profit. These vaccines have saved many lives and improved public health. The number of vaccines given to children has grown a lot, partly because governments have required certain vaccines for school entry.

Patents

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

Production

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

Making a vaccine takes many steps. First, the part of the germ that triggers an immune response, called an antigen, is created. 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 immune system respond better. The final step is putting the vaccine into small bottles for use. New methods, like using special cell cultures, are being developed to make vaccine production even better.

Delivery systems

One of the most common ways to give vaccines to people is by injection. Researchers are working on new ways to deliver vaccines that are safer and easier to use, such as using liposomes and ISCOM (immune stimulating complex).

Oral vaccines, which are taken by mouth, have been very useful. For example, an oral polio vaccine proved to be effective even when given by volunteers without special training. Oral vaccines have advantages like no risk of blood contamination and do not need to be kept very cold during transport, which can lower costs. Other new ideas include microneedle patches and dermal patches, which are still being tested and could make vaccines easier to give.

In veterinary medicine

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

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

In places where rabies is found, vaccinating dogs is often required by law. Dogs can also get vaccines for diseases like canine distemper, canine parvovirus, and Lyme disease. There have been rare cases where animal vaccines affected humans, but these are uncommon and not well studied.

DIVA vaccines

DIVA vaccines help tell the difference between animals that are infected with a disease and those that are vaccinated. These vaccines are missing a part that the real disease has, and a special test can detect if an animal has the vaccine or the disease. This method has helped countries get rid of certain diseases in their pig and cattle populations. Scientists are working to use this idea for more diseases in animals.

History

Further information: Vaccination § History, and Inoculation § Origins

Long before modern vaccines, people found ways to protect themselves from diseases like smallpox. One old method was called variolation, where a tiny amount of smallpox material was put into the nose or skin. This 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 as we know them 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 developed vaccines for other diseases, using weakened or parts of germs to teach the body to fight back. Through the years, vaccines have helped control and even erase diseases like smallpox, making our world much safer.

Trends

Since at least 2013, scientists have been working on creating new kinds of vaccines by building the outer structure of a virus. They hope this could help prevent problems where vaccines stop working well.

Researchers are also exploring how the body’s defense system can be used to create special vaccines for diseases that aren’t caused by germs, like some types of cancer and conditions where the body attacks itself. For instance, a test vaccine called CYT006-AngQb was studied to see if it might help with high blood pressure. Many things influence how vaccines are developed, including advances in medicine, changes in population, rules about health products, and how societies think about vaccines.

Plants as bioreactors for vaccine production

In 2003, scientists began looking into using plants to make vaccines. By adding special genes, plants like tobacco, potato, tomato, and banana can be made to produce substances that act like human vaccines. By 2005, bananas were created that could produce a vaccine for hepatitis B.

Vaccine hesitancy

Main article: Anti-vaccine activism

Vaccine hesitancy means putting off or refusing vaccines even when they are available. This can include not getting a vaccine at all, waiting a long time to get it, or only getting some vaccines but not others. Even though scientists agree that vaccines are safe and work well, when people hesitate to get vaccinated, it can lead to more people getting sick from diseases that could have been prevented. Because of this, the World Health Organization said in 2019 that vaccine hesitancy was one of the biggest threats to global health.

When many people avoid vaccines, diseases that were once rare can spread again, causing outbreaks and even leading to severe health issues from vaccine-preventable diseases. This is why it's important for everyone to understand how valuable vaccines are in keeping us healthy.