US regulators have authorised the first coronavirus vaccine for emergency use, marking an inflection point in the pandemic and kicking off what's set to be the largest vaccination campaign in US history.

The US Food and Drug Administration (FDA) OK'd a highly effective COVID-19 vaccine developed by the drugmakers Pfizer and BioNTech, FDA said Friday in a letter on its website. The decision follows an endorsement from an independent expert panel that reviewed data on the shot.

The leaders of Operation Warp Speed, the federal government's vaccine initiative, have said the plan is to ship 2.9 million doses of Pfizer's shot within days, starting an ambitious vaccination drive.

The US is aiming to vaccinate 100 million people by March: 20 million in December, 30 million in January, and 50 million more in February. Those projections depend on getting vaccines from Pfizer and from Moderna, a biotech company that also has a highly effective shot under FDA review. The shots will be free for people.

FDA Commissioner Stephen Hahn called the authorization "a significant milestone in battling this devastating pandemic."

"The tireless work to develop a new vaccine to prevent this novel, serious, and life-threatening disease in an expedited timeframe after its emergence is a true testament to scientific innovation and public-private collaboration worldwide," Hahn said in a statement.

Federal authorities are allocating vaccine doses to states and territories based on their adult populations, and each state will decide how to divvy up its supply. While the FDA said the vaccine can be given to people over age 16, a Centres for Disease Control and Prevention advisory group recommended that healthcare workers and nursing-home residents be at the front of the line.

The US faces challenges in distributing the shot and persuading people to get it

Health regulators in countries including the UK and Canada have already authorised the use of Pfizer's vaccine. The FDA's review took longer in part to ensure that there was a public discussion of Pfizer's application to help instil confidence in the shot.

Now the US faces the twin challenge of distributing the shot widely and persuading people to get it.

The logistical challenges are daunting. Pfizer's vaccine is given as two doses, 21 days apart, and needs to be stored at negative 94 degrees Fahrenheit (negative 70 degrees Celsius). Pfizer executives have expressed confidence that the temperature requirement won't be a major barrier in the US. The drugmaker is shipping the doses in special containers that can keep the vaccine stable for up to 30 days, if they're refilled with dry ice.

And polling has found that many Americans – perhaps as much as 40 percent or 50 percent of the country – have reservations about getting a COVID-19 vaccine.

Still, vaccines are likely to become a key piece of the US's effort to overcome the pandemic. The rapid vaccine development has been a bright spot among efforts that have been marred by early failures to develop coronavirus tests, shortages of protective gear, and a slow and inconsistent federal response.

Despite promise, plenty of unknowns surround the vaccine

Pfizer's vaccine was overwhelmingly protective against COVID-19 in a clinical trial that compared more than 20,000 people who got the shot with a similar group of volunteers who received sham injections. The trial found that the shot was about 95 percent effective at preventing symptomatic cases of the disease, though the real-world experience could be different.

There were no major safety concerns found in the study. Most people experienced some side effects that were expected, didn't last very long, and typically were mild to moderate in intensity. The most common were pain at the injection site, fatigue, and headaches.

Shortly after the UK started to immunize healthcare workers and older people, authorities said that people with a history of serious allergic reactions to other medicines or food should not get Pfizer's vaccine. The warning followed two reports of adverse reactions in healthcare workers who have a history of severe allergies.

The FDA issued a narrower warning, saying only that people shouldn't get Pfizer's shot if they have had a severe allergic reaction to a previous dose of this specific vaccine or to one of its ingredients.

There are still crucial questions about the vaccine.

For one, the long-term safety remains unknown, because most people in the trial have been monitored for only a few months. Typically, according to experts, the vast majority of side effects – but not all – occur within 42 days of getting a vaccine.

Pfizer, as well as providers giving the shot, are required to track and report any serious safety problems with the vaccine. The drugmaker is also required to conduct studies to look for any safety issues that may crop up.

It's also unclear how long the protection will last. The durability of the vaccine will become known only over time, and experts have wondered whether people will need booster shots later on.

The study also didn't rigorously assess whether Pfizer's vaccine prevents people from transmitting the virus or whether it can prevent asymptomatic cases. Experts say people should plan to continue to wear masks and practice social distancing even after getting the vaccine.

Mammoth logistical challenges and uncertainty cloud the rollout

Specifics on how the US plans to vaccinate its population remain scarce. In recent weeks, officials have given a range of projections for the pace and timeline, sometimes contradicting one another.

Warp Speed officials have said vaccinations could begin anywhere from one to four days after the emergency OK. While federal leaders have expressed confidence in their plans, much of the work will be left up to the states to actually determine where the doses go.

In a sign of Warp Speed's caution, more than half of the initial 6.4 million doses of Pfizer's vaccine are being held back. About 2.9 million shots are being retained to ensure that everyone can get their second booster dose on time, and another 500,000 are being kept "in reserve," Gen. Gustave Perna, Warp Speed's chief operating officer, said at a press briefing on Wednesday.

Usually, manufacturing plants produce stockpiles of a vaccine before it's shipped out. In the case of Warp Speed, the plan is for doses to be shipped out essentially as they come off the factory line.

While developing and authorizing a vaccine in under a year is an unprecedented feat, Warp Speed has already failed to live up to its public timelines. The initiative launched in May with the goal of delivering 300 million vaccine doses by the end of this year. Over time, officials have quietly walked back that goal.

Health and Human Services Secretary Alex Azar in August lowered that projection to "the high tens of millions of doses." In December, the vaccination target was lowered to 20 million people by the year's end – less than 10 percent of the original goal.

Twenty million doses won't be enough to vaccinate everyone in the CDC's highest-priority groups: It has estimated there are 24 million healthcare workers and residents in long-term care facilities.

Down the line, states will have to balance the interests of many groups vying for doses, particularly from industries that yield influence in certain states.

For instance, should bus drivers get the vaccine before white-collar workers in the financial services industry? What priority should be given to grocery store workers, or to teachers? A lack of federal guidance is leaving those thorny prioritisation decisions to state leaders.

No federal plan to win the trust of those hesitant about a vaccine

Earlier this year, the scientific process was battered by politics, with President Donald Trump touting vaccine progress as a key ingredient of his reelection attempt. But Trump is far from the only reason Americans are cautious about coronavirus vaccines.

Research done by the Reagan-Udall Foundation found six major themes driving distrust:

  1. Concerns about the speed of the process.
  2. Distrust of government.
  3. Distrust of the healthcare system.
  4. Concerns that politics and economics will be prioritised over science.
  5. Fear that the vaccine will not work for me or my community.
  6. Fear based on past experiences.

An FDA director told Business Insider that seeing someone who you know and trust – your doctor or a clergy member, for instance – get vaccinated would help rebuild trust over time.

While Warp Speed officials have talked about the need to communicate publicly about the vaccine, they have provided no specifics about outreach or education campaigns at a federal level.

With the first regulatory OK, coronavirus vaccines are quickly becoming a reality, in an astonishing scientific accomplishment. But myriad challenges involved in vaccinating the world lie ahead.

This article was originally published by Business Insider.

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