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Vaccinations and Immunizations

This research guide contains resources on vaccinations and immunizations and is a starting point for students researching this topic or for anyone wanting general information.

What is a Vaccine?

A vaccine is any preparation used as a preventive inoculation to confer immunity against a specific disease, usually employing an innocuous form of the disease agent, as killed or weakened bacteria or viruses, to stimulate antibody production.

Diseases that vaccines prevent can be dangerous, or even deadly. Vaccines greatly reduce the risk of infection by working with the body's natural defenses to safely develop immunity to disease.

Vaccines help develop immunity by imitating an infection. This type of infection, however, does not cause illness, but it does cause the immune system to produce T-lymphocytes and antibodies. Sometimes, after getting a vaccine, the imitation infection can cause minor symptoms, such as fever. Such minor symptoms are normal and should be expected as the body builds immunity.

Once the imitation infection goes away, the body is left with a supply of "memory" T-lymphocytes, as well as B-lymphocytes that will remember how to fight that disease in the future. However, it typically takes a few weeks for the body to produce T-lymphocytes and B-lymphocytes after vaccination. Therefore, it is possible that a person who was infected with a disease just before or just after vaccination could develop symptoms and get a disease, because the vaccine has not had enough time to provide protection.

Centers for Disease Control (CDC)

Additional Information

If they are not vaccinated, your child is at risk for developing a vaccine-preventable disease. Vaccines were developed to protect people from dangerous and often fatal diseases.These diseases remain a threat.Vaccines are safe and effective protection.

Influenza or “flu” is a serious respiratory disease that can be deadly. Healthy babies and toddlers are especially vulnerable to complications from influenza. Every year children in the United States die from influenza.

Pertussis or “whooping cough” is an extremely dangerous disease for babies. It is not easily treated and can result in permanent brain damage or death. Since the 1980s, the number of cases of whooping cough has increased, especially among babies younger than 6 months of age and adolescents. Since 2010, several states have reported an increase in cases and outbreaks of whooping cough, including statewide epidemics in California and Washington. Whooping cough has killed many babies since 2010; most deaths were in those younger than 3 months of age.

Measles is a highly contagious disease that can lead to serious complications, including death. It remains common in many countries and has been brought into the United States by returning vacationers and foreign visitors. Vaccination caused measles to decline rapidly during the 1990s. Recently, vaccine hesitancy among parents in the United States and abroad has led to a growing number of children and teens who are not vaccinated and are unprotected from measles. This has led to outbreaks of measles in the United States, Canada, and other countries.

Chickenpox is very contagious. Before the development of a vaccine, chickenpox killed approximately 100 people every year in the United States. Most were previously healthy. Children infected with chickenpox must be kept out of day care or school for a week or more so they don’t spread the disease to others.

Your child can infect others in the community Children who are not vaccinated can transmit vaccine-preventable diseases at schools and in the community. Unvaccinated children can infect babies who are too young to be fully immunized. Unvaccinated children can infect people of any age who can’t be immunized for medical reasons. This includes children and adults with leukemia and other cancers, immune system problems, and people of all ages receiving treatments or medications that suppress their immune systems.

Your child may have to be excluded from school or child care. During disease outbreaks, unvaccinated children may be excluded from school or child care to protect them and others. This can cause hardship for the child and parent. Next steps... We strongly encourage you to vaccinate your child. Please discuss any concerns you have with a trusted healthcare provider or call the immunization coordinator at your local or state health department. Your vaccination decision affects not only the health of your child, but also your family, your child’s friends, their families, and your community.

Immunization Action Coalition

The main reason why anyone talks about vaccines and autism is that some parents have noticed changes in children shortly after the children were vaccinated. Their kids seemed to be developing normally, then suddenly stopped interacting with people and lost language abilities -- a condition called "regressive" autism.

Most medical researchers argue that this is probably a coincidence: Autism symptoms tend to become apparent around the same time that children are scheduled to get routine vaccines.

Although there are two separate issues concerning vaccines and autism, they're often lumped together. One has to do with the measles, mumps, and rubella (MMR) vaccine; the other involves vaccines containing the chemical preservative thimerosal, which contains a form of mercury that has been suspected of causing autism and has recently been removed from most vaccines.

The MMR scare started 10 years ago with a report published in The Lancet that described the cases of eight children who, as their parents recalled, developed autistic symptoms and digestive ailments shortly after getting their first MMR dose. The researchers proposed that the vaccine might trigger a previously unknown form of regressive autism. They suggested that maybe the measles virus in the vaccine lodged in the intestine, causing some kind of reaction that then affected the brain.

After that, experts studied whether the MMR vaccine could cause autism. To do that, they looked for clues among kids who did and didn't get the vaccine.

Since that initial finding, 14 studies including millions of children in several countries consistently show no significant difference in autism rates between children who got the MMR vaccine those who didn't.

The bottom line: It's very unlikely that the MMR causes autism, researchers say.


Thimerosal is a mercury-containing compound that prevents the growth of dangerous bacteria and fungus. It is used as a preservative for flu vaccines in multi-dose vials, to keep the vaccine free from contamination.

Thimerosal is also used during the manufacturing process for some vaccines to prevent the growth of microbes.  In 1999, as a precautionar y measure, the U.S. Public Health Ser vice recommended removing thimerosal as a preservative from vaccines to reduce mercury exposure among infants as much as possible.

Today, except for some flu vaccines in multi-dose vials, no recommended childhood vaccines contain thimerosal as a preservative.  In all other recommended childhood vaccines, no thimerosal is present, or the amount of thimerosal is close to zero.  No reputable scientific studies have found an association between thimerosal in vaccines and autism.  

There are two different compounds that contain mercury: ethylmercur y and methylmercury. The low levels of ethylmercury in vaccines are broken down by the body differently and clear out of the blood more quickly than methylmercury

Centers for Disease Control (CDC)

Vaccinations aren't just for kids. The need for vaccines does not go away with age. In fact, there are specific ages in your adult life when vaccinations are recommended. Also, protection from vaccines you received as a child can wear off over time, and there are more vaccines available now.

The vaccines you need as an adult are determined by many factors including your age, lifestyle, health condition, and which vaccines you’ve received during your life. As an adult, vaccines are recommended for protection against:

  • Seasonal Influenza (flu) – Everyone 6 months and older should get a flu vaccine every year as the best way to reduce the risk of flu and its potentially serious complications.
  • Pertussis, also known as whooping cough – The Tdap (tetanus, diphtheria, and pertussis) vaccine is recommended for women during each pregnancy and once for all adults who have not previously received it.
  • Tetanus and diptheria – The Td vaccine is recommended every 10 years.
  • Shingles – The herpes zoster vaccine is recommended for adults 50 years and older.
  • Pneumococcal disease – Two pneumococcal vaccines are recommended for adults 65 years and older. One or both vaccines may be recommended for adults younger than 65 who have specific health conditions or who smoke cigarettes.

You may also need vaccines to protect against human papillomavirus (which can cause certain cancers), meningococcal disease, hepatitis A, hepatitis B, chickenpox, measles, mumps and rubella.

Getting vaccinated is one of the safest ways for you to protect your health. Vaccine side effects are usually mild (like soreness at the injection site) and go away on their own. Severe side effects are very rare.

It’s also important to protect yourself when traveling for work or pleasure. Depending on where you travel, vaccines can protect you from diseases that are rare in the United States, like yellow fever.

Centers for Disease Control (CDC)

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