Timing of hepatitis B immunizations

Our sons were given the first of the three shots necessary for a Hepatitis vaccination without having been told that there is a very specific amount of time for the second shot. The second shot was never issued. My wife again had the first shot administered by the same group but without the reminder my wife did not reschedule the second shot. Is it dangerous to have had two of the first shots? Do we continue by starting with shot one yet again?

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Robert Steele

Robert W. Steele, MD, is a board certified pediatrician at St. John's Regional Health Center in Springfield, MO. He graduated from medical... Read more

When a particular immunization is studied for how well it works, a number of things about that shot are tested. One of these things is what the optimal timing for that shot is in order to invoke the body's greatest immune response. The timing of immunizations is based upon two basic principles:

  1. Priming the pump -- The first shot or shots are given primarily just to expose the body to the contents of the immunization. The body reacts by first learning to recognize the foreign material of the shot and beginning to make infection fighting antibodies. This priming may take one shot like with the MMR, two shots like with the Hepatitis B vaccine, or three shots like with the DPT.
  2. Making the body remember -- The next step is to give a shot or shots to help the body remember the immunization which allows for the body to have a quick response should it come in contact with the actual real infection. These are called booster shots. Some vaccinations require only one booster like with the MMR. This vaccine seems to give good immunity throughout life without requiring extra boosters. Others require boosters throughout life like with the tetanus shot. There are some vaccines in which we don't know how long it lasts such as the chicken pox vaccine (see Should I give my child the new chicken pox vaccine?), and it may require boosters later in life.

However, with all these vaccines, the limits upon the timing of when the doses are given only involve how soon the next dose may be given. Doses may be given late without compromising the immunity inferred by the vaccine. Obviously, we would prefer to give the doses in as fast a manner as possible in order to protect children from these diseases, however, the body needs time in between doses to prime itself.

The "rules" for the Hepatitis B vaccine are that the second shot may be given no earlier than one month after the first one. And the third shot may be given no earlier than six months after the first and no earlier than one month after the second. All the shots are of the same material both in content and quantity (assuming they are not teenagers.) Therefore, as long as they did not receive the second shot too early, the timing of this shot may vary greatly without compromising the immunity they will get from the vaccine. In other words, assuming they followed the above rules, your sons did not get two of the first shot, but in fact, they got two shots in the series of three required for the hepatitis B vaccine. They now need one more shot to be given no less than six months after they received the first one.

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