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Most vaccinations are given in childhood. Many diseases are most common in early childhood and the immune systems of young children are still developing and may need an extra boost. Most states require that children receive certain vaccinations before they are allowed to attend daycare, school or camp.

Vaccination schedules are compiled by the Advisory Committee on Immunization Practices (ACIP), which advises the U.S. Centers for Disease Control and Prevention (CDC) and U.S. Department of Health and Human Services. Vaccination schedules reflect both the time that a person is first able to react to an antigen and the time when people are most likely to contract the disease. This is usually during early childhood, although there are some vaccinations that may need to be given again later in life.

A schedule of some standard childhood vaccinations is as follows:

Vaccinations that may also need to be administered later in life include:

• Influenza. Each year, influenza is believed to infect between 5 percent and 20 percent of the American population, making it one of the most common infectious diseases in the United States. It can largely be prevented by getting the flu shot in October or November, before the beginning of flu season, which can last from October to May.

The CDC recommends that people at high risk for the flu, including people over age 50 and those with chronic illnesses, receive a flu shot each year. The composition of the flu shot changes every year because the virus mutates easily and can become resistant to previous vaccines, making annual vaccination necessary for continued protection.

In addition, the American Academy of Pediatrics, American Academy of Family Physicians and the CDC’s Advisory Committee for Immunization Practice (ACIP) all recommend that children between the ages of 6 months and 23 months begin receiving an annual influenza vaccine. Children with chronic medical conditions (e.g., asthma, cystic fibrosis, diabetes) and children on long-term aspirin therapy for certain conditions (e.g., Kawasaki disease) should also receive the influenza vaccine each year. Some studies show that this vaccine can reduce the risk of getting the flu by up to 80 percent during flu season.

• Pertussis (whooping cough). There has been a recent upsurge in the number of cases of whooping cough after it was thought to be all but eliminated in the United States. It is believed that this may be due to the vaccine wearing off by early adulthood. As a result, college campuses and nursing homes have become fertile ground for outbreaks of whooping cough, which is then spread to infants who are not yet fully immunized. The ACIP recommends that all people over the age of 11 receive a booster shot of the pertussis vaccine.
  
  
• Diphtheria, tetanus. A booster shot is required every 10 years for life to maintain immunity against these diseases. Adults who are not current on their diphtheria or tetanus vaccinations or who did not receive their initial series of shots during childhood should receive these vaccinations every 10 years.
  
  
• Pneumococcus. Adults over 65 or those with long-term health problems, especially conditions that weaken the immune system, should receive this vaccination. According to the CDC, pneumococcus is one of the most common causes of death in the United States from a vaccine-preventable disease. Older adults may be particularly susceptible to life-threatening complications due to this disease.
  
  
• Measles, mumps and rubella (MMR). Measles, mumps and rubella are serious diseases in children and adults. The CDC recommends that people born after 1957 (when the diseases were more prevalent and natural immunity was common) who have not already received the MMR vaccine should be vaccinated. It is especially important for women of childbearing age to receive the vaccine because rubella can cause miscarriage and birth defects.
  
  
• Chickenpox (varicella). Although children are more likely to contract the chickenpox virus than adults, the disease is more serious in adults. Chickenpox in adults may lead to shingles, which can damage the eyes or other organs. Adults with chickenpox are also more likely to develop pneumonia. Before the introduction of the vaccine in 1995, approximately 50 adults died each year from chickenpox. Adults who do not remember receiving the vaccine or experiencing the disease should consult with their physician about whether they should be vaccinated.
  
  
• Meningococcal vaccine. In recent years there have been several cases of meningitis outbreaks in schools and colleges. This is thought to be a result of living in close proximity to other people (such as in a dorm room) at an age where immunity from childhood vaccination (usually given at age 11 or 12) may be waning. The American College Health Association now recommends that adolescents receive a meningococcal vaccination before they start college.
  
  
• Human papilloma virus (HPV). In 2006, the U.S. Food and Drug Administration (FDA) approved a vaccine to protect against several strains of HPV, a common sexually transmitted infection that may cause genital warts in men and women and can infect the cervix in women. Left untreated, HPV in women may lead to cervical cancer.

The vaccine is most effective when given before the onset of sexual activity, when a person has not been exposed to HPV. After the vaccine’s approval, the ACIP recommended that the HPV vaccine be routinely given to 11- and 12-year-old girls. The vaccine is approved for use in girls and women ages 9 to 26. It is given in a series of three shots over a six-month period.