Administered “when the virus is multiplying and spreading,” plasma from people who have recovered from the virus can be effective, said Ates Kara, a member of Turkey’s Science Board that’s overseen the country’s response to the pandemic. “But if you’re late, don’t expect a game-changing effect. Late administration can even increase complications.”

Turkey has been using various blood-treatment therapies on Covid patients, including removing, re-oxygenating and then reintroducing blood. But the biggest determinant of success is acting quickly, Kara said. Turkish doctors can use plasma and other interventions without waiting for test results to confirm a positive diagnosis, he said.

That provides Turkey with an advantage that might not apply in the U.S., where treatment costs and health insurance plans may discourage patients from visiting hospitals until their illness is more advanced, Kara said.

The U.S. Food and Drug Administration issued an Emergency Use Authorization for Covid-19 convalescent plasma for the treatment of hospitalized patients, and in a Sunday night press conference Trump hailed the move. It came as he lags in opinion polls ahead of November’s election with his handling of the pandemic a key issue.

Some experts accused Trump and the FDA of misrepresenting sketchy test data after they claimed the treatment could reduce mortality by 35%. FDA Chief Stephen Hahn later accepted the criticism as “entirely justified.”

“What I should have said better is that the data show a relative risk reduction not an absolute risk reduction,” he said.

Turkey has confirmed more than 259,000 cases of Covid-19 and 6,139 deaths. The U.S., with a population four times the size, has 5.7 million cases and almost 177,000 deaths.