From Happy Meals to children’s Tylenol, the general principle is that young ones need scaled-down versions of the products their parents consume. But research presented by infectious disease scientist Steve Black of Cincinnati Children’s Hospital Medical Center at the European Society for Paediatrics Infectious Diseases meeting last week provides evidence that, with vaccines, it may work a little differently.

In the 1970s, a flu challenge study found that adults who received a vaccination and achieved an antibody titer of 1:40 or above were 50% less likely than their counterparts to be infected when deliberately exposed to the pathogen—and that titer cutoff has been the flu vaccine golden standard ever since. Using data from a comparative vaccine efficacy study, Black and his colleagues calculated the antibody titers of over 4,000 children who had been given vaccines in a phase 3 clinical trial and compared their protection to their infection rate in the wild.

The retrospective analysis found that the children, aged ranging from six months to six years, needed a much stronger antibody titer of 1:110 to receive that same 50% protection as the adults. If further studies corroborate these results, we need to rethink vaccinations in children, Black says. “If you’re going to vaccinate, you’d better make sure that you’re using a vaccine that is immunogenic enough or strong enough to induce enough antibody to protect the children.”

Crucially, flu vaccines are developed and tested in adults, and later rolled out to the young and old. By comparison, Black says there doesn’t need to be a rethinking of dosage for non-flu vaccines as most of these are primarily tested for efficacy in children.

When it comes to flu vaccine, he’s not entirely sure why kids would need a larger immune response to fight off the flu, but he notes that “their bodies are starting from scratch with no prior immunity.”

Evidence for this idea could be seen during 2009’s H1N1 outbreak, during which the elderly did better than expected but children were hit pretty hard. Black says that H1N1 is “partially related to a virus that circulated in the 50s,” which would have given the older people prior immunity — although this kind of retrospective evaluation should always be taken with a grain of salt.

Retesting the influenza vaccines will be difficult — researchers will have to wait a few years for another clinical trial like this as challenging children with viruses is problematic — but Black hopes it will be done. “Children are not just small adults,” he says.

Image: Flickr user alviseni under Creative Commons