THE WORD “emergency” was emphasized in the headlines about the World Health Organization’s May 5 declaration on the spread of wild poliovirus, and rightly so. The high season for the spread of the virus is approaching, and the WHO emergency measures are aimed at deterring transmission of the virus and protecting the hard-won gains of recent years.

Actually, the polio situation this year has been promising in some places. In Nigeria, where the virus has been endemic, only two cases have been reported this year, following declines last year; in Afghanistan there has been some spillover from Pakistan but only one case of the endemic virus in more than a year. Dr. Bruce Aylward, assistant director-general of WHO for polio, said that in both countries “we’re at a level of control there that we’ve never seen” before. In Syria, where a civil war has raised concerns about the difficulty of carrying out vaccination campaigns, the last case was in January.

The dark heart of the polio scourge lies in Pakistan. According to Dr. Aylward, of the 74 cases of polio due to the wild poliovirus this year, 59 have been reported from Pakistan and within Pakistan; 46 of those 59 were from the Federally Administered Tribal Areas; and 40 of those from just one agency or semi-autonomous administrative unit. By contrast, no other country this year has reported more than Afghanistan’s four cases, and three of those came from Pakistan.

What caused the WHO to sound the alarm — this is only the second such emergency declared; the first was for the H1N1 influenza pandemic in 2011 — is the fear that travelers are spreading the wild poliovirus, threatening to export it to nations where it does not now exist. Many populations are at high risk of infection due to fragile states, war and broken immunization systems. The WHO estimates that about 60 percent of the cases last year were due to international travel. Although the virus mainly strikes young people, there was evidence that adult travelers were contributing to the spread.

The target of the global polio eradication program has been to stop transmission by this year, but Dr. Aylward said Pakistan is the one country that is really “off track.” Attacks on polio vaccination workers there have stymied vaccination campaigns, opening a door to the highly contagious disease. The government has made some efforts in Peshawar to beef up security and resume vaccination campaigns, but it is not enough.

The WHO has called for travel restrictions in Pakistan, Syria, Cameroon and elsewhere to stop the spread by those who fly or travel by land. It may be tempting for the affected nations to shrug and take half-steps, but the threat of polio spreading is very real and poses a danger not only for their own populations but also for peoples far beyond.