The global drive to eliminate polio, which has gone on for 31 years and consumed over $16 billion, has been set back again by a surge of new cases in Pakistan and Afghanistan.

As of July 10, there were a total of 42 polio paralysis cases in the two countries. They comprise a single large outbreak , because most cases are in the tribal areas along the border, where local people easily cross back and forth.

Pakistan had 32 of the cases, compared to only three by the same date last year, and the situation is expected to get worse because hot summer weather favors the virus. There were only 12 cases in the country in 2018 and eight in 2017.

For each paralyzed victim — usually a child below age 5 — there are about 200 others who are infected and shedding the virus in their stool, the World Health Organization estimates.