Vaccine Education Center

Questions and Answers About the Vaccine Schedule

I can’t find my vaccine record. Can I look at the history and determine which vaccines I had as a child?

No. The history is a good way to see which vaccines existed when you were a child, but that does not mean you had them. There are several reasons for this:

• A recommendation does not mean a requirement – The vaccines listed on the history were the recommended vaccines at the time; however, in many cases if a vaccine is not required, such as for school entrance, it is not commonly given.
• Even with a requirement, not everyone gets the vaccine – While a few of the vaccines are received by almost all children, not every child receives every vaccine. Even if 90 of every 100 children receive a vaccine, there are still 10 that did not.
• You may have had the disease – If not enough people are immunized, the diseases are still circulating in a community, so it is possible that you may not have had a vaccine, but you had the disease.
• Vaccines do not always work – Even if you have had a vaccine, your body may not have generated a strong enough immune response to afford you protection.

What are the differences between the DTP, DTaP, and Tdap vaccines?

All three of these are vaccines that protect against diphtheria, tetanus and pertussis. They differ in the quantities and purity of the components, whom they are recommended for and how many doses are given:

• Available in 1948, DTP was the first version of the combined diphtheria, tetanus, and pertussis-containing vaccines. This vaccine was known for causing several side effects. Approximately, one of every two recipients had a fever or swelling and pain at the sight of inoculation. A small number of children experienced a high enough fever that they had fever-induced seizures, and some experienced prolonged or inconsolable crying. Also, uncommon, but occurring on occasion was a state of unresponsiveness or collapse. These effects were found to be caused by the pertussis component of the vaccine.
• Because of the high rate of side effects, scientists developed a more purified version of the pertussis vaccine, referred to as the acellular pertussis vaccine. When this was combined with diphtheria and tetanus vaccines in 1997, it was called the DTaP vaccine. This version caused less side effects than the DTP vaccine and is the current version given to infants and young children.
• Adolescents and adults are recommended to receive a booster dose of tetanus every 10 years. The vaccine commonly used was the Td vaccine; however, there were two concerns. First, the more doses of diphtheria-containing vaccine given, the more likely the recipient was to experience significant swelling in the inoculated arm. Second, adults were getting pertussis, suggesting that protection from the pertussis vaccines they received during infancy and young childhood were not continuing to protect them throughout adulthood. Because adults pass the disease to newborns and young infants not yet protected by vaccines, there was interest in developing a pertussis vaccine for adults. The Tdap vaccine was developed to combat both the high rate of swelling from the diphtheria vaccine and the waning immunity to pertussis; it was introduced in 2006 and is now recommended for all adolescents and adults the next time they are getting their booster.

Why do we use the polio shot and not the oral polio vaccine?

In about 1 of every 2.4 million recipients, the live, weakened virus contained in the oral polio vaccine causes paralysis. The shot does not have this same side effect because, unlike the oral version, the shot contains killed virus which can not replicate and, therefore, can not cause paralysis.

Between 1961 and 1996, children in the U.S. received 4 doses of the oral vaccine. During 1997 and 1999 children typically received 2 doses of the shot followed by 2 doses of the oral version and since that time, infants have received 4 doses of the shot.

Many other countries continue to use the oral polio vaccine because it is more economical and, therefore, allows more people to get the vaccine.

Why was the rotavirus vaccine removed from the schedule in 1999 and then put back in 2007?

The first rotavirus vaccine, known as RotaShield®, was approved for use in 1998; however, less than one year later it was removed from the market because of an increased risk of a condition known as intussusception. Intussusception is an uncommon, yet painful intestinal blockage that occurs when the intestine folds into itself. This side effect of the vaccine was found to occur in about one recipient for every 10,000 doses administered. Because RotaShield caused this side effect, it was removed from the recommended vaccine schedule.

In 2006 and 2008, two new rotavirus vaccines were licensed. Both vaccines were made of different versions of the virus as compared to RotaShield, which contained monkey strains of rotavirus. In 2006, RotaTeq® was licensed containing cow strains of rotavirus. The latter vaccine to be licensed was Rotarix®, which contains a weakened human strain of rotavirus. Both vaccines were tested extensively before licensure to be sure they too did not increase the risk of intussusception. Both have been given to millions of children without the same side effect; therefore, rotavirus has been added back to the infant immunization schedule and is recommended for all infants.

Why was the hepatitis A vaccine recommended for all infants after it was given to only certain groups at first?

When the hepatitis A vaccine first became available, it was only recommended for sub-groups of the population that were at increased risk of getting hepatitis A. However, in 2006 the recommendation was extended to include all infants between 12 months and 23 months of age:

• The original version of the vaccine could not be given to children less than 2 years old. A newer version became available in 2005 that could be given to younger children.
• Disease rates had been controlled in parts of the country where the vaccine was recommended, yet cases of hepatitis A were still occurring.

Why is hepatitis B vaccine given to newborns?

Hepatitis B is primarily a sexually transmitted disease, so many parents question why their newborn infants need to get this vaccine at birth. Indeed when the vaccine first became available in 1982, only those at high risk of becoming infected were recommended to get the vaccine. Despite these efforts, about 1 of every 3 patients with acute disease was not in these high-risk categories. These efforts were not controlling disease because:

• Many people do not realize that they are infected,
• Some people are chronic carriers, and
• The disease can be spread by casual contact, such as sharing a washcloth, toothbrush, or razor with infected blood, even in quantities small enough that they can not be seen

Infants exposed at birth are particularly susceptible to chronic infection and death from liver disease as adults. However, testing women prior to giving birth would not prevent all cases of transmission to infants nor would it decrease exposure from other family members who may be infected. This was the case in some immigrant populations from countries in which hepatitis B was endemic. By beginning the immunization series with newborns, the risks to the child could be minimized and the number of chronic carriers in the community could be decreased as these children reached adulthood. Since the universal infant recommendation was made in 1991, public health officials are expecting to see decreases in liver cancer and disease rates as these children become adults.

Why has the age of the children who are supposed to get influenza vaccine changed?

Indeed the ages of children recommended to get influenza vaccine have been variable over the past several years:

• 2002: 6- to 23-month-olds
• 2006: 6- to 59-month-olds
• 2009: 6- month to 18-year-olds

These changes were coupled with increasing recommendations for adults. It is likely that ultimately there will be a recommendation for everyone to receive an annual influenza vaccine. Because there was not a supply of influenza vaccine to recommend it for the entire population, the recommendations had to gradually increase the number of people that should get the vaccine beginning with the most susceptible populations. As demand for the vaccine grows, so too will the quantity produced; however, because the vaccine is made in eggs, this increase had to take into account the availability of eggs - and the chickens that produce them of course!

Reviewed by: Paul A. Offit, MD
Date: October 2009