The nasal spray vaccine is most effective when administered to adults. The injectable vaccine is affordable for all adults. Any person who has received the injectable vaccine can safely receive the nasal-spray vaccine as well. Adults do not contract influenza primarily from children who have influenza.
Until now, only injectable vaccines against influenza have been available. Parents are reluctant to subject children to the pain of injections, but adults, who are at risk of serious complications from influenza, are commonly vaccinated. A new influenza vaccine, administered painlessly in a nasal spray, is effective for children. However, since children seldom develop serious complications from influenza, no significant public health benefit would result from widespread vaccination of children using the nasal spray.
Which of the following is an assumption on which the argument depends?