The U.S. government will ramp up efforts to screen travelers for the Ebola virus, a move experts say should have been made earlier. To further control the virus, President Obama said officials will add extra screening measures for passengers traveling to United States.

“We’re … going to be working on protocols to do additional passenger screening both at the source and here in the United States,” Obama told reporters at a Monday afternoon press conference without explaining the specifics of the plan.

Thomas Eric Dunan, a Liberian national who contracted Ebola, is reportedly in critical condition and being treated at a Dallas hospital.

Ebola is spread through contact with the bodily fluids of an infected individual but is contagious only after a patient starts showing symptoms. In a Sunday statement, the the Centers for Disease Control and Prevention said other passengers on Duncan's flight were not at risk because he was asymptomatic until after he arrived in the United States. The incubation period is as long as 21 days.

Duncan was mistakenly sent home after he visited the Texas Health Presbyterian Hospital with Ebola-like symptoms. The CDC is currently working with local authorities to track down anyone with whom he may have come into contact once he became contagious. It took five days for officials to send hazardous materials crews to clean up the apartment in which he was staying.

“The human errors in this single case highlight why it is urgent that we ban all commercial flights from the impacted countries until the outbreak is contained,” David Dausey, a Yale-trained epidemiologist and dean of the School of Health Professions and Public Health at Mercyhurst University in Erie, Pennsylvania, wrote in Monday's Washington Post.

“It’s time to take security precautions that align with the gravity of the threat,” he wrote. “That means doing whatever it takes to keep infected people from coming here.”

More than 3,400 people have died in Guinea, Liberia and Sierra Leone during the largest Ebola outbreak in history. There are more than 7,400 confirmed, suspected and probable cases, according to the World Health Organization.

Earlier in the outbreak, governments in West Africa and other regions put travel bans in place, but the World Health Organization said the restrictions do more harm than good.