The global tally of people infected with the coronavirus passed 15 million on Wednesday, while in the worst-hit pandemic hot spot of the United States, President Donald Trump warned the pandemic would "get worse before it gets better." With Covid-19 passing another shocking milestone, Mr Trump delivered his first virus briefing after a three-month hiatus, offering a shifted message on Tuesday, including professing a newfound respect for the protective face masks he has seldom worn. It came as polls have shown Mr Trump lagging behind Democratic rival Joe Biden ahead of November's election, and as the count of virus fatalities in the US passes 140,000. Even so, the president worked in jabs at the news media and Democrats, and repeatedly referred to Covid-19 as the "China virus." Elsewhere, the US government has agreed to pay almost $2 billion for 100 million doses of a potential coronavirus vaccine, German firm BioNTech said on Wednesday. BioNTech, which is developing the drug with US pharma giant Pfizer, said in a statement that American people would receive the future vaccine "for free" in line with the Trump administration's "commitment for free access for Covid-19 vaccines". Under the agreement, the US government has placed an initial order for 100 million doses to be delivered if regulatory approval is granted. Elsewhere, almost a quarter of people in New Delhi have had the coronavirus, according to a study that cast serious doubt on the official numbers both in the megacity and across India. India last week became the third country after the United States and Brazil to hit one million cases but many experts have long said that with testing rates low, the true number could be much higher. Blood tests on 21,387 randomly selected people across Delhi conducted by the National Center for Disease Control found that 23.48 percent of them had IgG antibodies - indicating past exposure to the virus. With Delhi's population of more than 20 million, the findings published Tuesday by the federal health ministry suggest that 4.7 million people have had the virus, almost 40 times the official tally of 125,000. While praising government restrictions that have limited the spread of the virus, the ministry said the study "indicates that a large number of infected persons remain asymptomatic". Australia reported a record 502 new coronavirus infections on Wednesday, nearly four months after the epidemic initially peaked, with authorities warning the country was entering a critical new phase. Most of the new cases were reported in the southeastern state of Victoria, where authorities have struggled to bring an outbreak in Melbourne under control despite an almost two-week lockdown in Australia's second-biggest city. Australia's new coronavirus infections previously peaked on March 28 when 459 cases were reported. Australia had since appeared to bring the virus under control and had eased restrictions. Like neighbouring New Zealand, it had won plaudits for its pandemic response. Victoria Premier Daniel Andrews announced 484 new cases and two more deaths in the state Wednesday, bringing its total of active cases to just over 3,400. Australia has now recorded almost 13,000 cases of the virus and 128 fatalities in a country of about 25 million. Hong Kong reported 113 new coronavirus infections on Wednesday, a new daily record as a sudden surge in cases shows no signs of slowing despite ramped up social distancing rules. The finance hub was one of the first places to be struck by the virus when it emerged from central China. But the city had impressive success in tackling the disease, all but ending local transmissions by late June. However, infections have spiked again this month and doctors say a new outbreak is spreading out of control in the densely packed territory of 7.5 million people. "Hong Kong is at the most critical moment," health minister Sophia Chan said as she appealed for people to "cancel all the unnecessary outings". Earlier this month officials reimposed social distancing measures, shuttering some businesses and reducing dine-in hours. Health officials have also ordered people to wear masks on transport and, from Thursday, in all public indoor venues. More than 800 infections had been confirmed in the last fortnight alone, more than a third since the virus hit the city.