Not a good sign

The drug combination was unable to cure four patients, who had all visited Africa, in early signs the (malaria) parasite is evolving resistance.

When the disease reappeared, they were brought back in and treated with other drugs (atovaquone/proguanil, artesunate and doxycycline, or quinine + doxycyline). So there's not an emergency. But...

Parasite isolates, all of African origin, harboured variants at some candidate resistance loci. No evidence of pfk13-mediated artemisinin resistance was found. Vigilance for signs of unsatisfactory antimalarial efficacy among imported cases of malaria is recommended.