A new study of 42 cases of Guillain-Barré syndrome in French Polynesia offers the strongest evidence to date that the Zika virus can trigger temporary paralysis, researchers reported on Monday. But experts cautioned that more evidence from other locations was needed to be conclusive.

Since last year, doctors have noticed an unusual increase in Guillain-Barré cases in several countries with Zika outbreaks, including Brazil, El Salvador and Venezuela. But as the World Health Organization reported on Friday, a large number of those patients have not yet been confirmed through laboratory testing to have Zika.

Guillain-Barré leaves patients unable to move, in extreme cases forcing them to depend on life support. While most patients eventually regain full movement, the condition can be fatal. In the patients studied in French Polynesia, none died, but 38 percent went to an intensive care unit and 29 percent needed help breathing.

This study, published in The Lancet, used a number of tests to try to determine whether the group of 42 patients who contracted Guillain-Barré during a Zika outbreak in 2013 and 2014 also had the Zika virus.