JOHANNESBURG — The true number of cases among Africa’s 1.3 billion people is unknown as its 54 countries continue to face a serious shortage of testing materials for the virus. However, the continent now has more than a half-million confirmed coronavirus cases. The total is over 508,000, according to figures released Wednesday by the Africa Centers for Disease Control and Prevention, after South Africa recorded another day of more than 10,000 confirmed cases as a new global hot spot. “A tremendous problem, a real crisis of access,” the World Health Organization’s Africa chief, Matshidiso Moeti, said last week. So far most testing has been concentrated in capital cities, but infections in many cases have spread beyond them. Africa’s health systems are the most poorly funded and thinly staffed in the world, and already more than 2,000 health workers have been infected by the virus, according to the WHO. This week alone, some anxious health workers in Nigeria, Zimbabwe, Congo and Sierra Leone have gone on strike or demonstrated for adequate protective gear or better pay. The African continent has just 2.2 health workers — and 0.3 doctors — per 1,000 people, according to the WHO. Experts have warned that even if badly needed supplies such as ventilators are provided to African nations, another challenge is having enough trained workers to operate them. Africa reaches the half-million-case milestone as a growing number of its countries decide to reopen their skies to commercial flights, saying their economies are sick, too. Months of closed borders bought time to prepare for the pandemic but hurt the delivery of badly needed humanitarian aid. — Agencies