Jan. 11, 2002 -- Children born a century ago were vaccinated just once, for smallpox. Today, children routinely receive 11 different vaccines -- or up to 20 separate shots -- before their second birthday.
It's no wonder that many parents feel uneasy about the multiple immunizations, and worry that their children's tiny immune systems might be overwhelmed. But those fears are unfounded, a report from Children's Hospital of Philadelphia concludes. The review found that studies do not support the hypothesis that the current roster of vaccines, "overwhelm, weaken, or 'use up' the immune system."
In fact, the researchers note, the multiple vaccinations given today actually have less impact on the immune system than the single smallpox vaccine of a century ago. That's because they have fewer of the antigens, or foreign proteins, that challenge the immune system and provoke it to respond by producing antibodies to remove them.
"When you compare vaccines you really have to compare the number of vaccine components they have," study leader Paul A. Offit, MD, tells WebMD. "When you do that, you find that the smallpox virus vaccine contained about 200 smallpox-specific proteins, each of which could induce antibodies. When you add up the proteins ... in the 11 vaccines given today, the number is about 120." Offit is chief of the infectious disease section at Children's Hospital of Philadelphia.
His team conducted the review in response to a recent national poll that showed one in four parents worry about their children getting too many vaccinations. Gilbert L. Ross, MD, medical director of the American Council on Science and Health, says many parents fear vaccines because of negative press generated by anti-vaccine interest groups.
"It is inaccurate to say that vaccines are 100% safe, but the benefits far outweigh the risks," Ross tells WebMD. "Any unexplained, devastating illness in a child between age 0 to age 5 is likely to occur within several weeks or months of getting a vaccination [because they receive them so often]. It is easy to understand why a parent might blame it on the vaccine, but there is no scientifically supportable evidence to back that up."
The report noted that infants and young children have an "enormous capacity" to respond safely and effectively to immune system challenges from vaccines. From the moment of birth, a newborn's immune system must respond to millions of different bacteria, viruses, and other microorganisms.
"Our immune systems are constantly being challenged, and they mount a vigorous immune response all the time," Offit says. "The vaccine response is really just a drop in the ocean compared to what our bodies normally encounter and manage every day."
The reviewed studies overwhelmingly found that infants and young children are capable of generating protective immune responses to multiple vaccines given simultaneously. Offit and colleagues calculate that infants could theoretically respond to as many as 10,000 vaccines at one time.
"Currently, the most vaccines that children receive at one time is five," Offit says. "Using this estimate, we could predict that even if all 11 of the routinely recommended vaccinations were given to infants at one time, only about 0.01% of the immune system would be used."
The review was published in the January issue of Pediatrics, the official journal of the American Academy of Pediatrics (AAP). The issue also included AAP's revised childhood immunization schedule for 2002. Changes include a recommendation that all newborns be vaccinated against hepatitis B before leaving the hospital. Due to a shortage of pneumococcal vaccine, the AAP also recommends that the fourth, or booster, dose be put off until more vaccine becomes available.