Public Release: 

Infant immune system is stronger than many parents think

Children's Hospital of Philadelphia

From the moment of birth, infants are capable of responding to numerous challenges to the immune system, including multiple vaccines, according to a new report published in the January issue of Pediatrics. The report, authored by Paul A. Offit, M.D., chief of Infectious Diseases and director of the Vaccine Education Center at The Children's Hospital of Philadelphia and colleagues, reviews current research on the effects of vaccines on the immune system and the capacity of the infant immune system to respond safely to multiple simultaneous immunizations.

"The number of recommended childhood vaccines has increased substantially over the past several decades. Twenty years ago, children received 7 vaccines routinely and up to 5 shots by 2 years of age. Today, children receive 11 vaccines routinely and as many as 20 shots by age two," explains Dr. Offit. As a possible consequence of these trends, recent national surveys have found that an increasing number of parents are concerned that infants receive too many vaccines. Implicit in this concern is the idea that an infant's immune system is inadequately developed to handle vaccines safely or that multiple vaccines may weaken, overwhelm or deplete the immune system.

"The infant immune system has an enormous capacity to respond safely and effectively to immune system challenges from vaccines," says Dr. Offit. "Our report offers reassurance to parents that far from weakening an infant's immune system, vaccines actually strengthen an infant's defenses against serious and potentially fatal infections."

The report, entitled "Addressing Parents' Concerns: Do Multiple Vaccines Overwhelm or Weaken the Infant Immune System?" highlights the following important findings:

Newborns commonly encounter a host of challenges to their immune system at the same time Newborns are capable of generating protective immune responses to bacteria and viruses, as well as vaccines, from the moment of birth. This capability is necessary for them to meet the tremendous number of environmental challenges they will encounter in the first few hours and days of life.

"Babies emerge from the relatively sterile environment of the womb into a world teeming with bacteria, viruses and other microorganisms, and their immune systems are designed to stand up to these challenges from the start," explains Dr. Offit. "Newborns have billions of immunologic cells that are capable of responding to millions of different microorganisms. By quickly making an immune response to bacteria that live on the surface of their intestines, for example, babies are able to keep those bacteria from invading their bloodstream and causing serious disease."

Current research shows that young infants are fully capable of generating protective immune responses to multiple vaccines given simultaneously. "Our analysis shows that infants have the theoretical capacity to respond to about 10,000 vaccines at once. Currently, the most vaccines that children receive at one time is five," says Dr. Offit. "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 .01 percent of the immune system would be used."

Infants today actually receive fewer substances in vaccines that stimulate an immune response than they did 40 or 100 years ago While there has been a substantial increase in the number of routine childhood vaccines over the past several decades, "Parents who are concerned about the growing number of vaccinations recommended for their children may take comfort in knowing that children are actually exposed to fewer antigens -- proteins that stimulate an immune response -- in the vaccines they receive today than in the past," says Dr. Offit. "Vaccine formulations have been refined and simplified over the years. Although we currently give children more vaccines than in the past, the actual number of antigens they receive has declined significantly. Whereas previously one vaccine, smallpox, contained about 200 antigens, now the 11 routinely recommended childhood vaccines contain fewer than 130 antigens combined."

Mild to moderate illness does not affect an infant's ability to generate protective immune responses to vaccines Some parents worry that vaccinating children who have minor illnesses makes it less likely that they will develop a protective immune response and more likely that they will develop an adverse reaction to the vaccine than healthy children. However, says Dr. Offit, data do not support this fear. "Studies have found that the presence of a minor to moderate illness such as an upper respiratory tract infection, ear infection, skin infection, fever or diarrhea does not compromise a child's ability to respond to vaccines or increase the risk of an adverse vaccine reaction."

"Because of the success of our immunization program, incidences of many vaccine-preventable diseases in this country are at an all-time low. This in turn has led some parents to question whether vaccines are really still necessary for their child," says Dr. Offit. "It is important to realize, however, that these vaccine-preventable diseases have not been eliminated. Some, like measles, mumps and rubella, continue to circulate at low levels in our population. Other, like diphtheria and polio, continue to cause outbreaks in other parts of the world and remain only a plane ride away. History tells us that if immunization rates were to drop, even by as little as 10 @ 15 percent, we would soon face a resurgence of these diseases and the devastating effects associated with them."

"Immunizations are extremely safe and highly effective at preventing disease and death, and are one of the most important steps parents can take to protect their children," says Dr. Offit. "Our report can offer parents reassurance that by immunizing their infants, they are affording them maximum protection against serious infectious diseases with minimum risk, helping their immune systems to become stronger, and giving them the healthiest possible start in life."


Co-authors of the report with Dr. Offit are Jessica Quarles, Michael A. Gerber, M.D., Charles J. Hackett, Ph.D., and Sarah Landry from the National Institute of Allergy and Infectious Diseases, Edgar K. Marcuse, M.D., and Tobias R. Kollman, M.D., from the University of Washington School of Medicine, and Bruce Gellin, M.D. from Vanderbilt Medical College.

About the Expert:

Paul A. Offit, M.D., is the director of the Vaccine Education Center and chief of Infectious Diseases at The Children's Hospital of Philadelphia. An internationally recognized expert in virology, immunology and vaccine safety, he is a member of the Advisory Committee on Immunization Practices to the Centers for Disease Control and Prevention. In addition to publishing more than 90 peer-reviewed scientific papers, Dr. Offit is co-author of the book "Vaccines: What Every Parent Should Know." He frequently lectures to national and international healthcare organizations about vaccine safety and efficacy.

Under the direction of Dr. Offit, The Children's Hospital of Philadelphia established The Vaccine Education Center in October 2000 to respond to the rapidly growing need for accurate, up-to-date, science-based information about vaccines and the diseases they prevent. The Center is a nationally recognized educational resource for healthcare professionals and parents, providing information on the full spectrum of vaccine-related topics. Approximately 400 people per day visit the Center's comprehensive Web site (

The Center has developed and distributed 1.5 million educational information sheets, "The Facts about Childhood Vaccines," to pediatricians, family practitioners and nurses nationwide.

The Vaccine Education Center has also created a first-of-its-kind educational video, "Vaccines: Separating Fact from Fear," for parents and healthcare professionals. To date, more than 20,000 copies of the video have been distributed to doctors' offices and health clinics across the country. Center staff members have presented findings at numerous scientific meetings, and conduct national speaker programs and educational symposia designed to help healthcare professionals address specific vaccine concerns.

Founded in 1855 as the nation's first pediatric hospital, The Children's Hospital of Philadelphia is ranked today as the best pediatric hospital in the nation by a comprehensive Child magazine survey. Through its long-standing commitment to providing exceptional patient care, training new generations of pediatric healthcare professionals and pioneering major research initiatives, Children's Hospital has fostered many discoveries that have benefited children worldwide. Its pediatric research program is among the largest in the country, ranking second in National Institutes of Health funding. In addition, its unique family-centered care and public service programs have brought the 381-bed hospital recognition as a leading advocate for children and adolescents from before birth through age 19.

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