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Childhood vaccines continue to improve

Many new vaccines have been introduced in recent years, causing parents to generally be more aware of their safety and effectiveness. The new study released on the safety of the acellular pertussis vaccine should be greeted with enthusiasm. The trend is clear; the data presented in this study shows that the new vaccine is safer.

Over the years, it was thought that most of the serious adverse events that occurred the same time whole-cell pertussis vaccine was administered were not actually caused by the vaccine. There is no question less serious, but still significant, side effects such as fever were caused by the vaccine. The decrease in side effects reported in the acellular pertussis study could be due to reporting bias. That is, doctors may be less likely to attribute the serious events to the vaccine if they know child received the acellular vaccine. Still, the results are encouraging.

Continuing evolution of vaccines
In the past 20 years, several new vaccines have been either introduced or altered in some way. These developments mark the continuing quest of doctors and scientists to provide the best possible protection against disease at the lowest possible risk. Indeed, the success of immunizations has caused some parents to become complacent about vaccinating their children. After all, when was the last time a child you knew had measles? However, in areas where vaccinations rates are low, it is possible to see flare ups of these diseases, which years ago caused thousands of deaths and disabilities.

How vaccines work
Vaccines are made from either viral or bacterial sources. Viral vaccines are produced from either live (attenuated) or inactive (killed) viruses.

• The measles, mumps and rubella (MMR) shot is an example of a live viral vaccine.
• The vaccine for diphtheria, on the other hand, is made from an inactivated form of the toxin produced by the diphtheria bacteria.
• The whole-cell version of the pertussis vaccine was made from the whole cell of the pertussis bacteria. The newer version uses only purified proteins taken from the bacteria.

Vaccines work this way. By placing a tiny amount of the virus or bacterial agent into the child, the child’s immune system is activated and produces antibodies to this specific substance. These antibodies stay with the child over the years and thus fight off the infectious agent if the child is later exposed. Immunizations are given early in life to protect children during their most vulnerable time.

With many vaccines, several doses are required. The first three of the four-dose DTaP are given at two, four and six months of age. The vaccine for measles, mumps and rubella (MMR) is first given at 12 months and then usually again at age four or five but certainly by age 11. Children who did not begin their immunizations at two months of age or who have had only some of their shots can still be fully immunized. It is never too late to get started.

New vaccines introduced
Haemophilus influenzae type b (Hib) has been a serious disease in children, frequently resulting in complications, including meningitis. But then in 1985, the first version of a vaccine was introduced, with a conjugate version added three years later. Before the vaccine, we used to see 200 cases of invasive Hib disease in Connecticut alone each year. Now you can count the number on one hand.

In 1995, the chicken pox or varicella vaccine was approved and added to the vaccination schedule. Initially there were concerns about how long a child would be protected, but the effectiveness seems to be holding up very well.

Hepatitis B vaccine was first created in the early 1980s and targeted at adults at high risk of this blood-borne disease, such as health care workers, people with multiple sex partners or IV drug users. When that campaign was deemed ineffective, it was determined in 1992 that all infants would receive the vaccine and thereby receive life-long protection.

The four-dose conjugate pneumoccocal vaccine is the newest vaccine to be introduced this year. Pneumococcal disease is responsible for about 200 deaths each year among children under five years old. Children under age two or children age two to five at high risk of this disease should be vaccinated. Talk to your doctor or health care provider if you believe your youngster should receive this vaccination.

Flu shots for children?
Flu shots are not routinely recommended for children because they are not at high risk for complications of flu. However, there are some benefits. Flu shots can reduce cases of flu in children, particularly in the day care setting and have been shown to reduce the number of ear infections. In addition, children immunized against the flu provide one less way for the virus to spread. A flu shot has to be repeated each year. However, with the shortage of vaccine this season and the cost involved, it is unlikely that children will be receiving flu shots in large numbers.

Combination vaccines
Several drug companies are investigating whether it will be possible to develop new combinations of vaccines that are given as one shot, rather than multiple injections. Before this can occur, the safety and effectiveness of each combination needs to be confirmed.

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Eugene Shapiro, MD, is a specialist in infectious diseases in children at Yale-New Haven Children’s Hospital and is professor of pediatrics at the Yale University School of Medicine.