<jats:title>A public health catch-22</jats:title> <jats:p> In 2016, the serotype 2 component of the oral poliovirus vaccine given to children was withdrawn. This measure was taken to prevent vaccine-associated disease outbreaks caused by mutation in the live attenuated vaccine. Children around the world now have poor immunity to serotype 2 poliovirus because the inactivated vaccine is far less effective and a new oral vaccine is not yet ready. Using a statistical model, Macklin <jats:italic>et al.</jats:italic> discovered that most current outbreaks of polio in several countries across Asia and sub-Saharan Africa are likely associated with the serotype 2 vaccine strain (see the Perspective by Donlan and Petri). To block transmission when poliovirus outbreaks occur requires deployment of the only tool in the box: the existing live attenuated serotype 2 oral vaccine, which increases the risk of vaccine-derived disease. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6489" page="401" related-article-type="in-this-issue" vol="368" xlink:href="10.1126/science.aba1238">401</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6489" page="362" related-article-type="in-this-issue" vol="368" xlink:href="10.1126/science.abb8588">362</jats:related-article> </jats:p>