Sign up for the Guardian Today US newsletter The Food and Drug Administration (FDA) commissioner, Stephen Hahn, marked the historic first US authorization of a Covid-19 vaccine – on one of the worst days of the Covid-19 pandemic – by assuring the American public of the vaccine’s safety. A vaccine developed by Pfizer/BioNTech was authorized Friday evening for emergency distribution, in a landmark development in the battle against the coronavirus pandemic. Hahn said the FDA is “to be congratulated” for the speed and thoroughness of its scientific review of the vaccine. But even as the vaccine is authorized, it will be met by a weary American public who, for nearly a year, has been bombarded by misinformation, much of it coming from Donald Trump, the US president, while witnessing a weak federal response and failure to contain Covid-19 transmission. “While this year has been marked by tragedy, sadness, sacrifice, it is also a year that has generated unparalleled scientific achievement that will resonate for many future generations,” Hahn said in a press conference on Saturday morning. “I will absolutely take this Covid-19 vaccine pending availability and distribution,” Hahn later said. “We worked quickly based on the urgency of this pandemic, not because of any other external pressure”. The vaccine authorized by the FDA is expected to be shipped directly from Pfizer US manufacturing facilities to states within hours, with healthcare workers and long-term care facility residents first in line to receive extremely limited early doses. The chief operating officer of Operation Warp Speed, Gus Perna, said the first vaccine doses are expected to arrive at 145 vaccination sites Monday, with more doses following on Tuesday and Wednesday to reach 636 sites across the country. “Make no mistake,” Perna added, “distribution has begun”. Stephen Hahn, the FDA commissioner. Photograph: Graeme Jennings/AP The vaccine is a two-dose regimen delivered 21 days apart. Pfizer is expected to deliver 2.9m doses of the vaccine in the first allotment, followed by an additional 2.9m doses to be given as a booster shot. The goal is to vaccinate 20 million people before the year is out – which is still short of the nearly 24 million people who make up the limited first group to receive the vaccine. The vaccine comes amid the worst surge of the pandemic to date. The same week the vaccine was authorized, more than 3,000 Americans succumbed to Covid-19 in one day, more than 200,000 people a day are being diagnosed with Covid-19, and nearly 300,000 people have died in total from the disease in the US. At a hearing of the FDA’s vaccine advisory committee, a Pfizer executive described the pandemic as “essentially out of control” in the US. The pandemic has not been under control nationally at any point since the first known cases were recorded in January. In spite of the extraordinary toll those figures represent, officials with the US Centers for Disease Control and Prevention (CDC) said this week the true toll of Covid-19 is likely two to seven times higher. The vaccine’s authorization also came after the White House reportedly pressured the FDA to move faster to authorize the vaccine. “Because of the suffering caused by this pandemic, FDA staff felt a sense of urgency to move through the authorization process,” said Peter Marks, the director of the FDA’s Center for Biologics Evaluation and Research, at the same press event, held online. “The FDA’s review process means Americans can trust and be confident in vaccines, not just Covid-19 vaccines but all vaccines reviewed by the United States,” he added. Peter Hotez, the dean for the national school of tropical medicine at Texas’s Baylor College and a vaccine expert not involved in the vaccine development, said FDA officials had done an “extraordinary job of balancing a response to a public health emergency and releasing a vaccine to the public they know is both effective and safe”. Even as shipments of the vaccine begin, Americans will not experience an immediately return to normalcy. Experts believe roughly 80% of Americans will need to be vaccinated to reach herd immunity, a process that will take months. This means Americans will need to continue to wear masks, hand-wash, social distance and avoid crowds, especially indoor gatherings. Public health departments, many of which will now be tasked with vaccine distribution, will also need to continue to test and perform contact tracing. The ‘daunting’ hurdles of distributing Covid-19 vaccines in America Further, for vaccines to significantly change the direction of the pandemic, the FDA will also need to authorize other vaccine candidates. An FDA vaccine advisory panel will notably consider recommending a vaccine candidate developed by Moderna, Inc and the National Institute of Allergy and Infectious Diseases, next week. The federal government has already ordered 200m doses. The Pfizer/BioNTech vaccine uses an innovative messenger RNA technology to introduce the body to the spike protein carried on the surface of the coronavirus. The vaccine must be shipped in specialized containers at ultra-cold temperatures of -70C (-94F). Vials, each containing five doses, must be used within days of being defrosted. Scientists are continuing to gather data on the vaccine as used in pregnant women and breastfeeding mothers, though research has so far not found as reason to issue a contraindication against pregnant women taking the vaccine. Following two cases of an allergic reaction in the UK, the FDA is also recommending people who have had severe allergic reactions to vaccines in the past speak to their healthcare providers before getting the vaccine. A Phase III clinical trial of the vaccine involving 43,000 people, and published in the New England Journal of Medicine, showed the vaccine had a 95% efficacy in preventing Covid-19. Several surveillance systems will also be in place to monitor safety and efficacy. Pfizer is expected to apply for full licensure of its vaccine next April.