Pfizer and BioNTech said Thursday that trials suggest that their vaccine is effective against a coronavirus variant that first emerged in South Africa, which some experts worry might evade existing shots. The drugmakers also said in a statement that 12,000 people involved in their Phase 3 trial experienced high levels of protection against Covid-19 six months after their second doses, with no serious safety concerns. "It is an important step to further confirm the strong efficacy and good safety data we have seen so far," said Uğur Şahin, CEO and co-founder of BioNTech. "These data also provide the first clinical results that a vaccine can effectively protect against currently circulating variants, a critical factor to reach herd immunity and end this pandemic for the global population," he said. The vaccine, developed by the American pharmaceutical giant Pfizer and its German partner, BioNTech, received emergency use authorization in December from the Food and Drug Administration, which is granted only in special circumstances.