LOS ANGELES — Screening travelers for the 2019 coronavirus is not very effective and will catch less than half of infected travelers, on average, and most infected travelers are not showing symptoms of the virus and are unaware they have been exposed, according to UCLA scientists whose research is currently under review.

The research calls for enhanced screening methods at airports and other travel hubs.

“This puts the onus on government officials and public health officials to follow up with travelers after they arrive, to isolate them and trace their contacts if they get sick later,” said Professor James Lloyd-Smith, a UCLA professor of ecology and evolutionary biology.

Many governments have started to impose quarantines, or even travel bans, as they realize that screening is not sufficient to stop the spread of the coronavirus. But in developing nations, a lack of infrastructure and resources for such measures make those countries vulnerable to importing the disease, Lloyd-Smith said.

“Much of the public health world is very concerned about the virus being introduced into Africa or India, where large populations exist do not have access to advanced medical care,” he said.

The researchers, including scientists from the University of Chicago and the London School of Tropical Hygiene and Medicine, have developed a free online app with which people can calculate the effectiveness of travel screening based on a range of parameters. The app is available at http://ow.ly/m3BG30qePg6.