The Hows and Whys of Baby Vaccines

Thanks to vaccines, many once-common childhood illnesses have virtually been eliminated. But because we don't see children suffering or dying from these diseases anymore, we don't fear them the way our parents and grandparents did. Instead, the vaccines scare us. Seventy percent of American parents who don't vaccinate their kids sincerely believe vaccines are more dangerous than the diseases they prevent, according to the National Network for Immunization Information (NNII). Many question whether they contain harmful ingredients that will cause their child to have a bad reaction, get a serious disease, or become autistic. Here are the answers to your most pressing vaccine questions.

How do vaccines work?

Babies are born with some antibodies (infection-fighting substances) in their bloodstream that were passed on to them in the womb from their mother. But as those inherited antibodies decrease in the first year of life, a baby must develop new antibodies and other infection-fighting substances. When he gets a cold or the flu, for instance, baby develops antibodies against the illness that protect him from getting the same virus as easily again.

However, there are some serious diseases you wouldn't want your child to catch just so he can become resistant to them. That's where vaccines come in.

Vaccines teach a baby's immune system how to recognize and fight off specific infections. Most vaccines are made from an inactive form of a virus, though a few (i.e., the measles vaccine) are made from a weakened form of a live virus. These vaccines don't cause disease but can stimulate a baby's body to recognize it.

Why get vaccinated for diseases no one ever gets?

Quite simply, if children stop getting their shots, these diseases can return.

More than 30 years ago, 10 percent of all children with Haemophilus influenzae type b (Hib) suffered brain damage, went deaf, or died. In 1985, the Hib vaccine was introduced, and Hib cases in the U.S. have dropped from an annual 20,000 to just a handful a year.

But even though nationwide vaccination efforts have largely eliminated diseases like Hib, polio, rubella, and diphtheria in the United States, these illnesses remain a threat because they still exist elsewhere, says Paul Offit, MD, director of the Vaccine Education Center at the Children's Hospital of Philadelphia. Children still die of communicable diseases in areas of the world where vaccination is not practiced or available. The only disease considered completely eliminated from the world is smallpox, so babies are no longer vaccinated for that.

So how does polio in far-off lands endanger American babies? International travel. "These diseases are just a plane ride away," says Martin Myers, MD, director of the National Network for Immunization Information (NNII). Even if you don't travel to areas where polio is prevalent, such as India, Africa, Southeast Asia, and the Middle East, your children can easily bump into foreign tourists or other American travelers who unwittingly bring diseases into the United States because they don't realize they're infected. For example, measles can be brought into the U.S. when an unvaccinated traveler visits an area that contains the disease and returns home. If he is still in the incubation period, then there is no sign of infection and the virus is contagious to others.

When should my child get her shots?

In the United States, we routinely vaccinate against 14 diseases. Infants are generally immunized at 2, 4, and 6 months; 9, 12, 15, and 18 months; and at 2 years of age. In some areas with a high rate of hepatitis A, two doses of a vaccine are recommended at age 2 or 3. Children get booster shots for the measles, mumps, rubella (MMR); diphtheria, tetanus, pertussis (DTP); and poliovirus vaccines before starting school.

Babies receive so many immunizations because they have a higher risk of getting sick and dying. "Their immune response isn't going to be as good as if they got them later, and that's why they need multiple doses," explains Stephen Turner, MD, chief of general pediatrics at Long Island College Hospital, in Brooklyn, New York. "But at least they have some immunity to protect them from serious illness."

Can my child get vaccinated if she's sick?

Kids can get vaccinated if they have the sniffles, even a low-grade fever. But reschedule if your child is really under the weather. Vaccines won't make her worse, but they also won't be as effective because her immune system is too busy fighting her current infection to produce the desired vaccine antibodies. If your child has a compromised immune system due to cancer, HIV, or immune-suppressing medication, she should skip live-virus vaccines like the MMR or chickenpox because they could make her ill. Kids with food allergies may also need to avoid certain vaccines that contain eggs (influenza), gelatin (MMR), or yeast (hepatitis B).

Will so many shots harm my baby?

Not at all. When infants are born, they are moving from a sterile environment (the womb) to the outside world, which is teeming with microbes. Within hours of birth, babies house bacteria in their intestines, which they've picked up from breathing, sucking, and swallowing; in turn, their body manufactures antibodies to keep the bacteria from causing infection. Newborns and infants have the capacity to form millions of different protective antibodies, but vaccines don't use up that potential.

I've heard there's an alternate schedule for vaccines. Is this a safer way to go?

Alternatives to the standard immunization schedule recommended by the Centers for Disease Control (CDC) (see "Schedule for Vaccines, 0-4 Years") are attractive to parents who believe that some vaccines are unnecessary or that so many vaccines at such a young age will overwhelm a baby's immune system. Alternate schedules, promoted online and in popular health books, suggest delaying the start of immunizations, avoiding some shots altogether, and spreading others out over the first few years of life so a baby doesn't get more than two shots at a time.

Sounds good in theory. But it's actually playing Russian roulette with your baby's health. "When you delay vaccines, you increase the period of time during which children are susceptible to diseases vaccines can prevent," Dr. Offit says. "Certain diseases -- like Hib, pneumococcus, and pertussis -- rear their head in the first year of life, so you need to immunize infants as quickly as possible."

Is it ever preferable for my child to get the natural disease?

No. The diseases we vaccinate children against can have serious consequences. Many parents today have had chickenpox. They recovered uneventfully, perhaps sustaining just a few scars from the pox.

But some children don't pull through quite so easily. In some cases, chickenpox can make children susceptible to infection and cause pneumonia. Since the chickenpox vaccine was introduced in 1995, however, the number of hospitalizations has gone down by 70 percent and the death rate has declined.

Will the shots hurt my child?

In truth, some shots -- like the combined MMR vaccine -- are more painful than others. Some pediatricians suggest giving an infant a dose of acetaminophen or ibuprofen after baby is weighed at the beginning of the visit. (It takes at least 30 minutes for pain medicine to work.) Even if the pain reliever doesn't kick in in time, it can help with the pain or slight fever (up to 101 degrees F.) that some babies experience afterward.

Will my child have any side effects from the vaccines?

For the most part, vaccines do their job with only minor side effects: typically soreness, redness, or a lump at the injection site, some crankiness, a low-grade fever, or, with the measles and chickenpox vaccines, a mild rash. Some infants will also be a bit sleepier than usual the next day. If your baby has a fever of about 101 degrees F. or seems uncomfortable within the first 24 hours, give him acetaminophen or ibuprofen. It may seem like vaccines are making your baby sick, but these reactions are a good sign that baby's immune system is working; symptoms usually subside within 24 to 48 hours.

However, if your child has a seizure or an allergic reaction such as wheezing, breathing problems, hives, rapid heartbeat, weakness, or dizziness within a few minutes to a few hours after receiving a vaccine, see your doctor immediately and contact the Vaccine Adverse Events Reporting System at 800-822-7967.

If your child has a history of serious allergies, particularly to eggs, gelatin, or certain antibiotics, such as neomycin, streptomycin, or polymyxin, tell your pediatrician before your child is vaccinated. There may be trace amounts of these elements in certain vaccines.

Why does every child need to be vaccinated? If most are, isn't my child protected?

In this country, rates of deadly diseases like polio, rubella, diphtheria, and Hib are very low. And other childhood maladies such as rotavirus and chickenpox are declining precisely because children's immunization rates are high. According to the CDC, 77 percent of children under 3 are fully immunized. This creates "community immunity," meaning that a virus won't spread within a community if enough people in the group have developed an immunity to it. So even if someone returns from, say, Italy, Switzerland, or Israel -- where there have been measles outbreaks -- the group is immune. Families that don't vaccinate create chinks in the community immunity where diseases can sneak in. "Diseases like measles and mumps bubble just below the surface," Dr. Offit says. "When immunization rates dip, those viruses come back."

That's exactly what health experts believe is fueling recent spurts of whooping cough as well as the largest measles outbreak this country has experienced in more than a decade. There were 136 measles cases in the first half of 2008. That may not sound particularly high when you consider that, worldwide, measles kills more than 300,000 children every year. But disease experts believe these cases are a troubling sign that immunization rates are falling below the levels necessary to keep measles at bay. Although on average only about 2.5 percent of families opt out of vaccines in states that allow for personal-belief exemptions, some communities have opt-out rates as high as 19 percent. Recent studies show that unvaccinated kids are up to 35 times more likely to contract measles than vaccinated children are. And indeed, nearly half the children caught up in last year's measles outbreak were unvaccinated. "If we could ever get everyone to vaccinate, the disease would be eradicated and we wouldn't have to vaccinate anymore," Dr. Turner says. "But because of exemptors, we're still going to be vaccinating generations down the line."

Parents may believe a decision to opt out and let kids "hide in the herd" affects only their family. But doing so weakens the herd and puts everyone at risk, particularly kids whose vaccines don't "take," babies too young to be vaccinated, and children with cancer and other conditions who can't be immunized and who depend on community immunity for protection. "It's not just protecting your child," Dr. Turner says. "It's protecting everyone's child."

There's so much scary stuff about vaccines on the Internet. How do I know what's true?

Consider the source before you believe a thing. Organizations like the American Academy of Pediatrics ( and CDC ( offer reliable scientific data. Be skeptical of information from parent groups, chat rooms, or alternative publications; and discuss any negative information you find with your pediatrician.

Although vaccination is about the safest medical procedure around, the CDC and the FDA are constantly monitoring the effectiveness and safety of vaccines, and manufacturers are always trying to improve them. There's also no reason to obsess about the "dangers" of vaccines.

For example, only one in a million children who receives the MMR vaccine develops serious complications like encephalitis, an inflammation of the brain. On the other hand, if they contracted the measles, about one in 1,000 children would develop encephalitis and one in 3,000 would die from the disease. So it's clearly better to vaccinate.

Do vaccines cause autism?

Perhaps parents' biggest concern about vaccines is whether they can cause autism. So let's be clear. Despite what you may have read online or heard on television talk shows, there's no credible evidence linking the two. The main study, lead by a British doctor named Andrew Wakefield, was published in 1998 and involved just a small sample of 12 children. By March 2004, most of the study authors had reversed their decisions, and in early 2010 the same British journal, The Lancet, that originally published his findings retracted his study. In January 2011, the British Medical Journal publicly denounced Dr. Wakefield's research as "fraudulent," saying he had "falsified data" and tampered with research results to give the MMR vaccine bad publicity. At the time of his study, Dr. Wakefield had been involved in a lawsuit against the manufacturers of the MMR vaccine and would have gained money if he'd won, making his research an obvious conflict of interest.

Meanwhile, more than 20 other studies involving thousands of children have consistently demonstrated that neither vaccines nor the preservative thimerosal (a type of mercury that is no longer used, except in some flu shots) causes autism.

So if that's the case, why did the Polings, of Athens, Georgia, who claimed that a five-shot vaccine series triggered their daughter Hannah's autism, win a payout from the federal government's Vaccine Injury Compensation Program (VICP)? Doesn't that prove a connection? No, and this is why: the VICP maintains a list of vaccine-related injuries that are automatically compensated, with basically no questions asked. In the Poling case, Hannah's rare enzyme deficiency caused her brain dysfunction. And it got worse when she developed a fever after her measles shot, so her family qualified for compensation.

Read more about vaccines and autism here:

Schedule for Vaccines, 0-4 Years

Hepatitis B

Dose 1: Birth

Dose 2: 1-2 months

Dose 3: 6-18 months

DTaP (diphtheria, tetanus, acellular pertussis)

Dose 1: 2 months

Dose 2: 4 months

Dose 3: 6 months

Dose 4: 15-18 months

Dose 5: 4-6 years


Dose 1: 2 months

Dose 2: 4 months

Dose 3: 6 months

Dose 4: 12-15 months

Varicella (chickenpox)

Dose 1: 12-15 months

Dose 2: 4-6 years

Hepatitis A

Dose 1: 12-23 months

Dose 2: 6 months after first dose


Dose 1: 2 months

Dose 2: 4 months

Dose 3: 6 months


Dose 1: 2 months

Dose 2: 4 months

Dose 3: 6 months

Dose 4: 12-15 months

IPV (polio)

Dose 1: 2 months

Dose 2: 4 months

Dose 3: 6 months

Dose 4: 4-6 years


Dose 1: 6 months

Dose 2: 4 weeks after first dose

Once per year, 1-5 years

MMR (measles, mumps, rubella)

Dose 1: 12-15 months

Dose 2: 4-6 years

Originally published in American Baby magazine.Updated 2010. Reviewed and updated in 2012.

All content, including medical opinion and any other health-related information, is for informational purposes only and should not be considered to be a specific diagnosis or treatment plan for any individual situation. Use of this site and the information contained herein does not create a doctor-patient relationship. Always seek the direct advice of your own doctor in connection with any questions or issues you may have regarding your own health or the health of others.

American Baby

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