In the first three months of life the only immunization shots the infant ordinarily receives are the OPT, which protects him against diphtheria, pertussis (whooping cough), and tetanus, and the Trivalent OPV against poliomyelitis (infantile paralysis) On the immunization schedule recommended by the Child and Family Health Division of the Children’s Hospital Medical Center. he will receive the DPT and Trivalent OPV twice more in his first year and boosters at eighteen months and again before entering school. Thereafter boosters should be given at intervals for the rest of his life. Any immunization is a deliberate stimulation of the body’s defenses against a specific harmful germ. We know that many diseases occur only once in any one person’s life.
From this fact. observed over many years and among millions upon millions of. people. the scientists who first developed vaccines concluded that when a person recovers from certain diseases he thereafter is immune to them. The basic idea of immunization is to set up these conditions artificially and safely, just as if the child (or adult, for that matter) were being infected by the harmful germ but without having to undergo the illness. The ideal immunization would stimulate the immunity without causing any symptom of sickness.
Most of the vaccines we use do come close to this ideal but never quite achieve it. There are some vaccines with undesirable side effects. but. except for the very rare patient. these side effects are not nearly as serious as the disease that the vaccine has been developed to prevent. The body responds to the vaccine much as it would to any foreign body: that is, it produces antibodies directed specifically against that foreign body. The antibodies react with or unite with the foreign substance (toxin, bacteria, or virus in this case) and inactivate either the germ or the germ’s toxic product. By “tagging” the substance and sealing it off, the antibodies render it less harmful and mark it for removal from the system.
And having once been produced to rescue the body from invasion by this specific foreign body, the antibodies thereafter remain on call, so to speak, to respond immediately to any new invasion by the same enemy. In other words, the body has organized a specific defense against a specific germ—it has become immune. Many vaccines, besides stimulating the production of antibodies, also stimulate changes in the immunity of the individual cells of the body. A type of allergy develops such that mere contact with a microbe or its toxic product elicits a reaction capable of destroying the invader. The vaccines for immunization are of two types, killed and live. Killed vaccines consist of concentrates of dead germs, which may be either bacteria or viruses. or of their toxic products. Certain bacteria produce chemical poisons that do the actual damage: these poisons are the toxins. The whooping cough vaccine, for instance, is made of the killed germs of the disease, whereas the diphtheria and tetanus vaccines are made of toxic products, not the bacteria themselves. The toxin is modified to stimulate immunity without causing the harmful effects of the unmodified toxin. In this condition it is called a toxoid.
Live vaccines consist of living viruses. These are harmless close relatives of the harmful viruses that cause full-blown disease. Because a dose relationship exists between the two viruses, the body responds to both in the same way: exposed to either, it becomes immune. The difference is that whereas the harmful virus would cause a serious illness, the vaccine virus produces only a mild local reaction, sometimes with fever. Smallpox is a severe. disfiguring, even fatal disease. Small-pox vaccine (although no longer given routinely) , in contrast, causes a single soon-healed sore, perhaps with low fever and mild discomfort. Yet both stimulate similar immunity.
This is the crucial point. Another important difference is that vaccine viruses. in general, are not transmitted from person to person as disease viruses are. For successful immunization it is not enough merely to stimulate production of antibody—a certain amount of the antibody must be produced. This amount is called the protective level. More than a single injection of certain vaccines (notably DPT) is required to stimulate development of the protective level of immunity. For others (notably the measles vaccine) one shot is enough. It seems likely that some vaccines (measles and mumps. for example) confer immunity for life. With others the immunity gradually wean off until it drops below the protective level.
Then a booster injection is required to stimulate antibody production back up to the protective level. Immunization against tetanus and diphtheria requires regular boosters throughout the person’s lifetime. Smallpox vaccination also had to be repeated when it was routinely given. The following immunization schedule or a close variation thereof is standard for children in the United States. The DPT, which is the only immunization that comes within the age limits set for this book, is given to infants by injection into the thigh.
Children cry on being punctured, but most of them experience no ill effect from the shot. A small minority exhibit slight irritability and may have mild fever twelve or twenty-four hours after the inoculation. Occasionally there will be redness and some swelling at the site of the inoculation. These symptoms usually subside in a day or two. They should be reported to the doctor at the next checkup. He may lower the dose for the subsequent shots. Because whooping cough is mainly a disease of quite young children, boosters for this immunization are not given after the age of five. We have gone into this subject at some length because immunization, which should be started in the infant’s second or third month, is a lifetime undertaking