Cubans are fleeing because of a steep economic downturn. Immigration is a big issue as leaders meet at this week's Summit of the Americas — but communist-controlled Cuba isn't invited.

Dozens were injured in the blast that ripped away large sections of the outer wall at the Hotel Saratoga, a 19th century structure. A gas leak was the suspected cause of the explosion.

The study by the National Academies of Sciences comes after dozens of U.S. diplomats in Cuba and China complained of migraines, dizziness and memory loss.