BENGALURU/LONDON - The United States has secured almost a third of the first 1 billion doses planned for AstraZeneca's experimental COVID-19 vaccine by pledging up to $1.2 billion, as world powers scramble for medicines to get their economies back to work.While not yet proven to be effective against the coronavirus, vaccines are seen by world leaders as the only real way to restart their stalled economies, and even to get an edge over global competitors. After President Donald Trump demanded a vaccine, the US Department of Health and Human Services agreed to provide up to $1.2 billion to accelerate British drugmaker AstraZeneca's vaccine development and secure 300 million doses for the United States."This contract with AstraZeneca is a major milestone in Operation Warp Speed's work toward a safe, effective, widely available vaccine by 2021," U.S. Health Secretary Alex Azar said.The vaccine, previously known as ChAdOx1 nCoV-19 and now as AZD1222, was developed by the University of Oxford and licensed to AstraZeneca. Immunity to the new coronavirus is uncertain and so the use of vaccines is unclear.The U.S. deal allows a late-stage, or Phase III, clinical trial of the vaccine with 30,000 people in the United States.Cambridge, England-based AstraZeneca said it had concluded agreements for at least 400 million doses of the vaccine and secured manufacturing capacity for 1 billion doses, with first deliveries due to begin in September.Now the most valuable company on Britain's blue-chip FTSE 100 Index, AstraZenecahas already agreed to deliver 100 million doses to people in Britain, with 30 million as soon as September. Ministers have promised Britain will get first access to the vaccine.VACCINE SCRAMBLEWith leaders across the world surveying some of the worst economic destruction since at least World War Two and the deaths of more than 327,000 people, many are scrambling for a vaccine.The U.S. government has struck deals to support vaccine development with Johnson & Johnson (J&J), Moderna and Sanofi, sparking fears the richest countries will be able to protect their citizens first.Sanofi's chief angered the French government earlier this month when he said vaccine doses produced in the United States could go to U.S. patients first, given the country had supported the research financially."We have a lot of things happening on the vaccine front or the therapeutic front," Trump told reporters at the White House when asked about the AstraZenca announcement. "You're going to have a lot of big announcements over the next week or two" on therapeutics.Trump, during a Thursday visit to a Ford Motor Co plant in Michigan, said the US military is "in gear so we can give out 150 to 250 million shots quickly."AstraZeneca said it was in talks with governments and partners around the world - such as the Serum Institute of India - to increase access and production and is speaking to various organizations on fair allocation and distribution."We would like to thank the US and UK governments for their substantial support to accelerate the development and production of the vaccine," AstraZeneca Chief Executive Pascal Soriot said.The Serum Institute of India, the world's largest maker of vaccines by volume, has dedicated one of its facilities with a capacity to produce up to 400 million doses annually to producing the Oxford vaccine."We are scaling up on a conservative basis of about 4 to 5 million doses a month to begin with," Chief Executive Adar Poonawalla told Reuters, adding the company was in discussions with AstraZeneca.COVID-19 PROTECTION?A Phase I/II clinical trial of AZD1222 began last month to assess safety, immunogenicity and efficacy in over 1,000 healthy volunteers aged 18 to 55 across several trial centers in southern England. Data from the trial is expected shortly.There are currently no approved treatments or vaccines for COVID-19.Governments, drugmakers and researchers are working on around 100 programs. Experts are predicting a safe, effective means of preventing the disease could take 12 to 18 months to develop.Only a handful of the vaccines in development have advanced to human trials, an indicator of safety and efficacy, and the stage at which most fail."AstraZeneca recognizes that the vaccine may not work but is committed to progressing the clinical program with speed and scaling up manufacturing at risk," it said.Other drugmakers including Pfizer Inc , J&J and Sanofi are in various stages of vaccine development.U.S.-based Inovio Pharmaceuticals said Wednesday its experimental vaccine produced protective antibodies and immune system responses in mice and guinea pigs.And Moderna this week released positive data for its potential vaccine, which it said produced protective antibodies in a small group of healthy volunteers.