Health officials in the Democratic Republic of Congo began a vaccination drive to control an Ebola outbreak that has infected more than 50 people and killed as many as 25. But as aid workers and health experts say this vaccination drive is a careful, methodical process in which trust is a key element. Health officials in the rural corner of northwest Congo that has been hit with Ebola say workers are seeking out those at the highest risk to vaccinate, a move that tries to cut off the virus at the pass while also making good use of the limited supply of the vaccine. At the moment, officials have only 7,500 doses of the experimental vaccine. World Health Organization spokesman Tarik Jasarevic explained the campaign, which began this week in the rural communities of Bikoro and Iboko. “This is not a general mass immunization, as is being done for some …