The head of the Africa Centres for Disease Control and Prevention (Africa CDC) on Thursday rejected an assertion by Tanzania’s president that his nation’s coronavirus tests are faulty and are giving too many false positives.

“The tests that Tanzania is using we know they are working very well,” Dr. John Nkengasong told journalists on a conference call.

The Africa CDC, along with the Jack Ma Foundation, a charity run by a Chinese billionaire, supplied the tests, Nkengasong said.