By Ted Hesson and Matt Spetalnick WASHINGTON, April 9 (Reuters) - The United States is considering a conditional cash transfer program to help address economic woes that lead migrants from certain Central American countries to trek north, as well as sending COVID-19 vaccines to those countries, a senior White House official told Reuters on Friday. The potential program would be targeted at people in the Northern Triangle region of Guatemala, Honduras and El Salvador, Roberta Jacobson, the White House's southern border coordinator, told Reuters in an interview, without saying who exactly would...