Why Do Some Vaccines Have to Be Injected Twice?

 What is active immunity?

The whole essence of immunization is the development of antibodies to a particular infection. Antibodies are specific proteins produced by the body in order to disarm disease-causing factors (viruses and bacteria) and toxins that they inject into the bloodstream.

All antibodies are ailment-specific. What does this mean? It means that particular infectious illnesses stimulate the production of special antibodies to the very same disease, and to this disease only. For example, antibodies to mumps can fight only the virus of mumps, but they are useless in the case of rubella.

Active (natural) immunity is immunity that is obtained in a natural way. If your baby undergoes an infectious disease, he or she will get immunized against that disease, as the body generates those little organisms (antibodies) that fight for our lives and health. The next time your child is exposed to the same disease, his or her immune system, having previously made its acquaintance with the organism, will recognize it and will trigger the production of antibodies to the disease.

Another kind of active or natural immunity is vaccine–induced. Half-killed, weakened, or even active germs injected into the bodies of children provoke the production of antibodies to a particular causative agent the same way the real disease would.

Natural immunity is normally long-lasting or even life-long.

What is passive immunity?

This is a type of immunity that the immune system of your child does not produce itself. Instead of the vaccination that triggers the generation of antibodies by the immune system, already-active antibodies are given to the child. Such antibodies are called immune globulins, which are prescribed when there is an urgent need for protection from a certain disease. Immune globulins are advantageous compared with active immunization with vaccines, as they can be given immediately and do not take long to produce full immunity against the infection. However, the main drawback of such an immunization is that it does not last long, as the effect fades away within weeks or months, whereas natural immunity is long-term or life-long.

Also, the way a fetus is protected with the mother's antibodies is also passive immunity. The placenta is the mediator for different antibodies that pass from mothers to their babies intrauterine (when the babies are in the womb).

Why are some vaccines injected twice?

Apparently, there are four reasons for this:

    • Some of the shots do not provide full-blown immunity after the first injection. These are usually primarily inactivated vaccines. For example, the vaccine against bacteria Hib, which causes meningitis, does not work after only the first time. To complete the procedure of antibody production against the bacteria, the second shot is required.

    • Toxoid vaccines like TDaP (tetanus, diphtheria, and pertussis) require repeated injections, as the immunity they provide tends to fade away with time. This is why a “booster” dose is necessary to bring back the body's resistance to the right level. After the initial infant immunization (4 shots), the next ones are conducted when children are between 4 and 6 years old, then another dose of Tdap (a booster for older children, teens, and adults) is given at 11-12 years age.

    • Even a live vaccine like MMR (mumps, measles, and rubella) does not provide strong-enough immunity to the three ailments, so a booster shot is required to stimulate the body to generate the necessary amount of antibodies to fight off the viruses.

    • Flu vaccines are given annually, as the appearance of the viruses causing the illness is changing and, according to the predicted type of the germ which would provoke a current outbreak, the vaccines are created. Children older than 6 months and adults have to be vaccinated every year. Those who have not been immunized after 8 months to 8 years age have to get two shots in a single year in order to get the strongest effect.

The logic behind double doses of vaccine

We have heard of the same vaccine being injected into a person more than once. But the question is, is it safe? That depends on the vaccine. There are certain vaccines that help achieve immunity in one shot. Then there are others that do not provide the complete dose in one go. As discussed above, these vaccines have to be administered again to complete the dosage and to provide the maximum benefits for the whole cycle. Not all live vaccines given may be able to provide an equal measure of cure in one go. Since vaccines help in the production of antibodies toward a specific disease, they are needed in the right amounts. Therefore, a repeat dose or first dose coupled with a second one completes the cycle. This is best understood after a medical examination or thorough check up.

Administration with care

Irrespective of the type of vaccination to be administered to the young one or adult, it is necessary to seek medical advice. Get in touch with your doctor and ask him for a prescription. He will perform a thorough check-up and recommend the dosages accordingly. The worst way to tackle the situation is to get a vaccination done without medical advice or proper care. Follow-ups are necessary as well. Certain vaccinations induce fever, while others cause sores or rashes. However, they may also manifest in harsh ways and lead to secondary infections. Handling such infections takes long and is not that easy. Thus, proper care and symptom-reporting are key to making sure that the vaccines have not harmed you instead of having done you good. Be it a vaccine against the flu, or one meant for measles or mumps, or any other, if it has to be taken, it has to be recommended by the doctor, and there is no other way about it. Many countries impose strict laws and regulations on vaccination and require it before foreigners can enter their territory. If you intend to travel, you should be aware of the regulatory requirements of the country you are planning to visit, and consult your doctor to check your vaccination history and current medical condition. If you lack any vaccination required by the country you are traveling to, you will have to undergo it.