Amid a resurgence of public concerns regarding the safety of vaccines, a handful of parents have started organizing 'natural immunity' parties to expose their children to contagious diseases—such as measles and chicken pox—and thus minimize the need for shots. These types of get-togethers have, of course, been organized for many years. The difference now is that the parties are organized around illnesses for which vaccines exist.

Andrea of Portland, Oregon, who declined to give her last name, hosted a chicken pox play date last summer when her five-year-old son came down with the illness after being exposed at school. Right away she emailed two friends, each with two boys, who wanted to expose their children in order to build natural immunity. The boys shared popsicles, kazoos and bubble blowers, and shortly thereafter they all came down with the disease.

For some parents, the fear that vaccines contribute to the risk of autism motivates them to organize these natural-immunity parties for their children, despite the fact that medical analyses have repeatedly refuted the vaccine links (Lancet 364, 963–969; 2004; N. Engl. J. Med. 357, 1281–1292; 2007). Others distrust the pharmaceutical industry or, like Andrea, take a holistic approach to childrearing, where less is more. “We chose to do only select and few vaccinations,” she says, “so that our son could build his own immune responses.” Even though her son attends a private school, she had to sign a waiver attributing her vaccine choices to 'religious reasons'.

Party favors: Children swap germs Credit: Corbis

Common childhood diseases like chicken pox and measles are highly contagious and can bear some dangerous consequences. Complications may include high fever, respiratory tract and ear infections and, in rare cases, brain inflammation and seizures.

Because of this risk, the American Academy of Pediatrics urges parents to vaccinate. Henry Bernstein, who serves on the association's Committee on Infectious Diseases and as chief of general pediatrics at the Dartmouth-Hitchcock Medical Center in Lebanon, New Hampshire, says that parents who don't vaccinate are “taking a chance in exposing their children to a vaccine-preventable disease that has known complications.”

In 2008 the US Centers for Disease Control and Prevention (CDC) has reported 64 confirmed measles cases through April, the most reported in this four-month period since 2001. Approximately 92% of children in the US receive vaccination for measles, but that figure may be dropping as more parents opt out.

With relatively few cases in the US, parents have to be resourceful to find a child with chicken pox or measles. Some rely on word of mouth through friends and family while others use online forums.

Still, a trend is emerging. According to one study, there has been a steady increase since the early 1990s in the number of school children who are not vaccinated because of personal belief exemptions, which must be filed with individual states before a child can attend school (J. Am. Med. Assoc. 296, 1757–1763; 2006).