Vaccines expose the body to dead or weak germs to help prevent or fight disease. The CDC recommends people of all ages receive vaccines at different stages of life. In rare cases, vaccines may cause severe side effects and death. The National Vaccine Injury Program (VICP) may compensate people for vaccine injuries.

Vaccination syringe and pills
Vaccine Facts
  1. Uses Vaccines help prevent disease.
  2. Serious Side Effect Shoulder injury related to vaccine administration (SIRVA), autoimmune disease, allergic reactions, fainting
  3. Largest Manufacturers Sanofi, Merck, GlaxoSmithKline, Pfizer and Novartis

Vaccines use weak or dead germs to help the body’s immune system fight or prevent disease. Vaccinations most often come in the form of a shot.

Vaccine mandates require children and adolescents to get vaccines to attend school or college in the U.S. Laws require some health care workers to get them as well.

Drug companies manufacture about 1 billion doses of vaccines each year worldwide. There are 81 vaccines licensed for use in the U.S., according to the U.S. Food and Drug Administration (FDA).

The FDA and the Centers for Disease Control and Prevention (CDC) take many steps to make sure vaccines are safe and effective. Vaccines approved for use in the U.S. undergo years of careful testing.

The government recommends vaccinations to protect people from potentially deadly diseases. It says the benefits outweigh the risks in most people.

But it’s important to note vaccines may cause serious side effects in rare cases. There are also controversies surrounding vaccines, particularly concerning autism.

The government compensates people for certain vaccine-related injuries. It does so through the National Vaccine Injury Compensation Program (VICP).

How Do Vaccines Work?

Vaccines work by exposing the body to small amounts of weak or dead germs, toxins or diseases. These germs imitate an infection. The body thinks it is fighting off the real disease. So, the immune system produces antibodies to fight the infection.

Once the imitation infection is gone, the body remembers how to fight it.

It may take a few weeks to produce antibodies after vaccination. This means people infected during or shortly after getting vaccinated may still get the disease.

Woman Testing Chemicals in Lab
The FDA rigorously tests vaccines for imperfections.

Live-Attenuated vs. Inactivated Vaccines

Live-attenuated vaccines use a weakened, live form of a disease to build immunity. These vaccines provide long-lasting immune responses with just one or two doses.

These vaccines use live germs. So, people with weak immune systems or health problems should talk to their doctors before receiving them.

Examples of live-attenuated vaccines include: measles, mumps, rubella (MMR), chickenpox vaccines (varicella) and shingles vaccine Zostavax.

Inactivated vaccines use the dead version of a disease to build immunity. These vaccines do not provide as strong a protection as live vaccines. Often, people need several doses over time.

Examples of inactivated vaccines include: flu (shot only), polio and rabies.

Polysaccharide, Conjugate and Other Vaccines

Polysaccharide and conjugate vaccines use parts of germs to build immunity. These parts include sugars, proteins or the outer casings of germ cells. Subunit and recombinant vaccines also use parts of germs.

Examples of these vaccines include: hepatitis B, HPV, Hib and pneumonia (pneumococcal).

Toxoid vaccines use chemically modified germ toxins to create immunity. The toxins are no longer toxic but still trigger the body’s immune system.

Examples of toxoid vaccines include diphtheria and tetanus.

Vaccines for some conditions may include different types. For instance, some meningitis vaccines (Menactra and Menveo) are conjugate vaccines. The Menomune meningitis vaccine is a polysaccharide. And the Bexsero and Trumenba meningitis vaccines are serogroup (recombinant) vaccines.

What Are Vaccines Made Of?

Vaccines are made of weak or dead germs and other inactive ingredients. Some ingredients are to make the vaccine effective. Others help to preserve the vaccine. Vaccines may also include ingredients that are part of the production process.

Ingredients for Vaccine Effectiveness

Antigens and adjuvants are ingredients that make the vaccine effective. Antigens are weak or dead germs that cause disease. For example, the flu virus is an antigen. Adjuvants help the immune system respond to the vaccine. Aluminum is an example of an adjuvant.

Vaccine Preservatives

Vaccines may contain preservatives and stabilizers. Preservatives such as thimerosal (a form of mercury) protect vaccines from bacteria and fungi. Stabilizers protect vaccines from temperature changes that may reduce effectiveness. Sugar and gelatin are examples of stabilizers.

Ingredients Used to Produce Vaccines

Vaccines may contain small amounts of ingredients manufacturers use to produce vaccines. These small amounts aren’t harmful, according to the U.S. Department of Health and Human Services. Such ingredients may include antibiotics, formaldehyde and traces of eggs.

Are Vaccines Safe?

“Data show that the current U.S. vaccine supply is the safest in history,” according to the CDC.

The FDA is in charge of approving and regulating vaccines.

Scientists test vaccines for several years in clinical trials before the FDA approves them for use in the U.S. These trials include thousands of people.

Once the FDA allows a vaccine on the market, manufacturers test each batch. They make sure the vaccine works and that it is pure and free of outside germs.

Monitoring Vaccine Safety

The U.S. has one of the most advanced systems for monitoring vaccine safety, according to the U.S. Department of Health and Human Services. There are several national monitoring programs to track vaccine side effects and safety.

The largest is the Vaccine Adverse Events Reporting System (VAERS). People who are aware of side effects linked to a vaccine can use VAERS to report them to the FDA. The FDA monitors the data for possible vaccine injuries.

Vaccine Side Effects and Injuries

Even with extensive testing, vaccines may still cause side effects in some people. The CDC says the benefits of vaccination outweigh the risk of injuries.

The most common vaccine side effects may show up within hours of the vaccination and go away a few days after. These include low fever, soreness around the injection site, headache and tiredness.

In rare cases, more serious side effects may occur. Some may even be permanent.

Serious vaccine side effects include:
Shoulder injury related to vaccine administration (SIRVA)
SIRVA may occur if a person receives a vaccine too deep or high on the arm. Symptoms of SIRVA are severe shoulder pain and difficulty moving the arm. People with SIRVA notice symptoms within 48 hours after vaccination.
Vasovagal Syncope (fainting)
Fainting may occur after vaccination. The CDC recommends sitting or lying down for about 15 minutes to prevent these injuries. Symptoms of syncope include dizziness and ringing in the ears.
Allergic reactions
Allergic reactions are possible after vaccination. Symptoms include skin rashes and difficulty breathing. These occur from a few minutes to hours after receiving the vaccine. According to the CDC, this occurs in one in a million doses.
Guillain-Barré syndrome (GBS)
Guillain-Barré syndrome (GBS) is an acute inflammatory disease that affects nerves. It causes numbness and weakness in legs and arms. Most people recover but some may continue to suffer nerve damage.
Chronic inflammatory demyelinating polyneuropathy (CIDP)
CIDP occurs in people with chronic GBS. This disease is progressive. People may continue to suffer nerve damage, pain and limb weakness.
Transverse myelitis
Transverse myelitis is inflammation of the spinal cord. Symptoms include pain, weakness in limbs, and bladder and bowel problems. Symptoms may develop suddenly or over days or weeks.

National Vaccine Injury Compensation Program (VICP)

The government set up the National Vaccine Injury Compensation Program (VICP) to provide financial compensation to people with certain vaccine injuries. The VICP covers most recommended vaccines.

Vaccine injury lawyers help individuals and families file VICP claims. By law, attorneys who help people file VICP claims do not charge petitioners a fee. Instead, the government pays their fees.

People have filed more than 19,000 petitions since 1988. VICP has paid out about $3.8 billion in vaccine settlements in that time. The Health Resources and Services Administration reported this data in March 2018.

Vaccine Recommendations by Age

The CDC recommends vaccines for infants, children, adolescents and adults. The CDC updates its immunization schedule when new vaccines are available or when the agency finds more effective doses. The CDC provides recommendations by age.

View Our Health Guides for More Health Recommendations:

Are Vaccines Mandatory?

All states have laws that enforce vaccine requirements. Vaccine mandates vary based on where you live.

Most children must receive vaccinations to attend daycare and school. Most colleges also have vaccination mandates.

State laws do allow some exemptions for health, religious or philosophical reasons.

Some nurses, doctors and other health care workers may also be required to receive vaccines as a condition of employment.

How to Pay for Vaccines

Most private and military health insurance plans cover recommended vaccines at little or no cost. Medicare and Medicaid also cover vaccines at little or no cost.

People without insurance can receive vaccinations for free or at a lower cost through local or federal government programs. Resources include:

Please seek the advice of a medical professional before making health care decisions.

Michelle Llamas, Senior Content Writer
Written By Michelle Llamas Senior Writer

Michelle Llamas has been writing articles and producing podcasts about drugs, medical devices and the FDA for seven years. She specializes in fluoroquinolone antibiotics, vaccines and products that affect women’s health such as Essure birth control, transvaginal mesh and talcum powder. Michelle collaborates with experts, including board-certified doctors, patients and advocates, to provide trusted health information to the public. Some of her qualifications include:

  • American Medical Writers Association (AMWA) Engage Committee and Membership Committee member
  • Centers for Disease Control and Prevention (CDC) Health Literacy certificates
  • Original works published or cited in The Lancet, British Journal of Clinical Pharmacology and the Journal for Palliative Medicine
Edited By
Medically Reviewed By
Dr. Ashrav Ali
Dr. Ashraf Ali Psychiatrist

11 Cited Research Articles

  1. U.S. Department of Health and Human Services. (2018, March 1). Data & Statistics. Retrieved from
  2. U.S. Department of Health and Human Services. (n.d.). Vaccine Ingredients. Retrieved from
  3. U.S. Department of Health and Human Services. (n.d.). Vaccine Safety. Retrieved from
  4. CDC. (2018, February 12). Possible Side-effects from Vaccines. Retrieved from
  5. CDC. (2018, February 6). Recommended Immunization Schedule for Children and Adolescents Aged 18 Years or Younger, United States, 2018. Retrieved form
  6. CDC. (2018, March 5). Recommended Immunization Schedule for Adults Aged 19 Years or Older, United States, 2018. Retrieved from
  7. CDC. (2013, February). Understanding how vaccines work. Retrieved from
  8. U.S. Department of Health and Human Services. (n.d.). Vaccine Types. Retrieved from
  9. National Institute of Neurological Disorders and Stroke. (2018, March 6). Transverse Myelitis Fact Sheet; What is transverse myelitis? Retrieved from
  10. Johns Hopkins Medicine. (n.d.). Guillain-Barre and CIDP. Retrieved from
  11. CDC. (2016, November 15). State Vaccination Requirements. Retrieved from
View All Sources
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