Withholding vaccination puts everyone at risk

ONE DAY last month, I awoke to an e-mail from a mother in my 15-month-old son's playgroup, with a subject line of "chicken pox." It alerted the other six families in the group that her son had been exposed to chicken pox two weeks earlier, and that he had now contracted it. I was concerned that she hadn't told the group about her son's exposure earlier, but figured it was a brief contact she assumed wouldn't infect him.

I later learned the exposure was far from a passing one. Her son's 4-year-old friend had developed his first spot on the family's way to a joint ski vacation for the two families, who shared an apartment for six days when he was most contagious. The playgroup mom's 15-month-old was at risk because the mom had decided to separate the components of the measles-mumps-rubella-varicella vaccine normally given at the age of 12 months, likely in response to fear generated by the question of the vaccinations' relationship to autism. While delaying the vaccine until 15 months is acceptable according to the American Academy of Pediatrics, for this child it meant contracting the varicella virus, which causes chicken pox.

The issue is particularly relevant because the academy recently recommended that children receive two doses of the chicken pox vaccine, rather than just one, because the additional dose bolsters immunity and may help reduce breakthrough infection.

A parent doesn't need to be a doctor to know that six days' exposure to another boy would almost certainly translate into an infection. Still, it's just chicken pox, right? And my son was vaccinated, so he was safe in any case.

That's not what concerns me, though. I was more concerned for parents in the group who might be pregnant, have diseases or conditions that weaken their immune systems, or live with elderly relatives. These are people for whom exposure to chicken pox and other vaccine-preventable illness could be potentially devastating.

By choosing to postpone or withhold vaccines -- usually based on scientifically unproven fears that they are linked to autism -- parents are depending on a phenomenon called "herd immunity." If target vaccination levels are reached for specific diseases, the portion of the population that has been vaccinated (the herd) will protect the people who have not. The population vaccination level for most vaccine-preventable diseases must be in the range of 80-95 percent to achieve this goal.

In the United States, vaccination rates should in theory be quite high. Yet in the case of chicken pox, it can be dangerous to rely on herd immunity, because the disease is much more severe in the very young and the very old. These are precisely the people who are either too young to have been vaccinated (under 12 months), or whose immunity may have waned over the years (the elderly). If a majority of children are vaccinated, but some are not, the burden of disease can move into these high-risk populations where infection can have severe consequences. Similar patterns hold for other illnesses that can be prevented by vaccines.

There are other factors that argue for the importance of vaccination as well: air travel, including international travel, is increasingly common, and presents a vector for infection: children's immunization records are not routinely checked before they board a plane. In some countries without resources for adequate immunization programs, high rates of vaccine-preventable infection persist. Vaccines are meant to protect individuals who receive them, but are also meant to protect public health.

If parents decide to postpone vaccines -- or, even worse, withhold them from a child -- without clear medical reasons, they should be obligated to share this information with families in close contact with their child, especially if this child is exposed to vaccine-preventable illness. The onus is on public health organizations and pediatricians who administer vaccines to continue to educate parents that any risk associated with vaccines is much less than the risk of contracting and spreading one of the diseases they prevent.

Dr. Maria Raven is an emergency medicine physician and a fellow in medicine and public health research at New York University and Bellevue Hospital Center.