In the pile of paperwork parents tackle before kids start school is a complicated chart they cannot ignore: an immunization schedule. Each state requires children to receive certain vaccines before they can attend classes, to protect the child as well as other children from preventable diseases.
Thousands of babies and children died or were seriously disabled each year before the widespread use of vaccines in the 20th century, according to the March of Dimes. Vaccines stimulate the immune system to produce antibodies against a specific disease by introducing a weakened or dead germ into the body.
Vaccinations made from weakened live viruses, such as the chickenpox or measles-mumps-rubella vaccines, can potentially sicken children with a form of the disease that is much less severe than that caused by the virus itself, according to the Nemours Foundation. Vaccines made with killed bacteria or viruses cannot cause illness.
However, vaccines that use live germs stimulate a stronger immune response than killed vaccines, so they may confer life-long immunity with only the need for a single booster shot. For viral diseases, live vaccines are also easier to create than vaccines with dead germs, according to the National Institutes of Health.
Parents may refuse to immunize their children based on medical, philosophical or religious reasons, according to the Centers for Disease Control and Prevention. However, the vast majority comply with requirements, which typically include vaccinations against diphtheria, pertussis, tetanus, measles, mumps, rubella, polio, hepatitis B and Haemophilus influenzae type B.
What these vaccines protect against and when are they needed:
Diptheria, tetanus and pertussis: These illnesses are tackled together in the form of the DTaP vaccine, which is administered at 2, 4 and 6 months of age; again between 15 and 18 months; between 4 and 6 years; and between 11 and 12 years.
Diptheria and pertussis (also known as whooping cough) are acute, highly contagious respiratory diseases. Tetanus, also called lockjaw, is caused by a toxin released by bacteria that are typically transmitted through deep puncture wounds. It causes muscle spasms and can be fatal.
Measles, mumps and rubella: This trio is also prevented through a combination shot given between 12 and 15 months and again between 4 and 6 years.
All three illnesses are highly contagious and used to be extremely common. Rubella, also known as German measles, can cause birth defects in the babies of infected pregnant women.
Polio: Extremely common before a vaccine was developed in the mid-20th century, the polio virus can cause paralysis or death. Its vaccine is administered at 2 and 4 months; between 12 and 15 months; and between 4 and 6 years.
Hepatitis B: A serious liver infection that can lead to cancer or cirrhosis, hepatitis B vaccine is given at birth; between 1 and 2 months; and again between 12 and 15 months.
Haemophilus influenzae type B: Also known as Hib disease, this bacterial infection was the leading cause of meningitis in children under 5 before a vaccine was developed, according to the CDC. Hib vaccine is given at 2, 4 and 6 months; and again between 12 and 15 months.
Some states may require school children to also be immunized for:
Pneumococcus: These potent bacteria, which can cause pneumonia and meningitis, are staved off with a vaccine typically given at 2, 4 and 6 months; and again between 12 and 15 months.
Rotavirus: One of the most common causes of severe diarrhea, rotavirus vaccine is given at 2, 4 and 6 months.
Varicella: A vaccine for varicella, the chickenpox virus, was developed in the 1990s. It is administered between 12 and 15 months and again between 4 and 6 years.
Hepatitis A: A highly contagious liver infection, hepatitis A is prevented with a vaccine given in two doses between 12 and 24 months.
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