CAPE TOWN, South Africa (AP) — Health officials and experts around the world are welcoming a U.S. plan to donate 500 million more COVID-19 vaccines to developing countries. But the celebrations Thursday came with hesitation. For instance, when exactly will those vaccines reach regions left behind in the global race and that are feeling the bite right now with deadly new waves of virus infections? And how many other wealthy nations will follow the lead of the U.S. to fill the gaping need? Dr. John Nkengasong of the Africa Centers for Disease Control and Prevention called the Biden administration’s promise to purchase and share Pfizer vaccines “clearly a cause for celebration.” He added he was eager to understand the exact timeline for the vaccines hopefully heading to his continent.