When will US citizens be able to get Covid-19 vaccine?

Americans are desperate to know when a coronavirus vaccine will be available to finally curb the pandemic that has already taken nearly 200,000 lives in the United States, and allow schools and the broader economy to reopen.

Scientists and vaccine makers have long said that a handful of vaccines could be available by the end of the year, if everything goes according to plan. But in recent weeks, President Donald Trump has insisted that a vaccine will be ready before the presidential election Nov. 3, raising fears that one could be rushed against the advice of scientists and regulators.

Testing and producing a vaccine is a complex process with a lot of uncertainties. But the best guess for now, experts say, is this: If every aspect of the vaccines’ development and distribution goes exactly as planned — and history has shown that rarely happens — certain people in high-risk groups could get vaccinated this year. Most other Americans, however, will quite likely have to wait until well into next year.

Q: What has Trump said?

A: At a news conference Wednesday evening, Trump doubled down on that unrealistic timeline, saying that a vaccine could be ready by mid-October and that it would then be made available “immediately” to the general public.

“We’re not looking to say, ‘Gee, in six months, we’re going to start giving it to the general public,’” he said. “No, we want to go immediately.”

In doing so, he contradicted his own director of the Centers for Disease Control and Prevention, Dr. Robert Redfield, who had testified to senators earlier in the day that a vaccine would most likely not be available until the middle of next year. Trump’s statements also contrasted with comments made Wednesday morning by officials with Operation Warp Speed, the federal effort to accelerate a vaccine, who said that supplies would be limited in the first months that a vaccine is available.

It was not the first time the president had pushed an accelerated timeline. Just the night before, at a town hall meeting hosted by ABC News, he said one could be available in three to four weeks.

Q: What do scientists and vaccine companies say?

A: Redfield’s timeline is consistent with the best guess estimates from other vaccine experts, who say that the general public won’t have access to the vaccine until February at the very earliest, and possibly more like July or August.

Of the three companies with vaccines in late-stage clinical trials in the U.S., just one — Pfizer — has said that it could have initial results by the end of October. The other two companies, Moderna and AstraZeneca, have been more vague, saying only that they hope for results before the end of the year. If a coronavirus vaccine were to show results this year, it would shatter the previous record of four years for the development of a new vaccine.

Dr. Paul Offit, a professor at the University of Pennsylvania and a member of the Food and Drug Administration’s vaccine advisory panel, was skeptical that Pfizer could be so sure of its timeline. “I think it’s irresponsible — they don’t know,” he said. “I think the more responsible answer is, ‘Hopefully, we’ll know something by the beginning of next year.’ That would seem to me to be the most likely scenario.”

Moderna’s top executives said in interviews this week that they could have initial results by November. But a trial blueprint the company released Thursday indicated an even longer timeline, suggesting that the first analysis of the trial data may not be conducted until late December, and that there may not be enough information then to determine whether the vaccine works. Later analyses, projected for March and May, are more likely to provide an answer, the company said in its blueprint. (A company spokesman said the November estimate is an updated assessment of what was in the blueprint.)

AstraZeneca’s timeline is also in question after it halted global trials this month because of a participant who had developed severe neurological symptoms after receiving the experimental vaccine. The company has not released details about the medical condition of the person, nor has it said whether the reaction was because of the vaccine. The trials have since resumed in the United Kingdom and in Brazil, but not in the U.S., where it has been paused since Sept. 6.

Q: What could delay or speed up the timeline?

A: While clinical trials are underway, independent panels of experts periodically check in on the data. If the vaccine shows signs that it is extremely effective, the board could decide it would be unethical to continue the trial and keep giving some participants a placebo. This outside panel could also ask a company to stop a trial if it was not preventing COVID-19 cases, or if there were serious safety concerns.

Whether the vaccine is effective is determined by comparing how many people in each group — the vaccine group and the placebo group — develop the disease. If many more people in the placebo group get infected, that means the vaccine works. As a result, the trials’ speed is determined by how fast the virus is spreading in the communities where trials are underway. Organizers try to guess where infections are on the rise and set up trials there, but in a fast-moving pandemic, that’s not always easy.

Trial pauses for safety reasons — like the one recently announced by AstraZeneca — could also slow down the timeline, even if the safety problems are ultimately found to be unrelated to the vaccine.

Q: How long will it take for the FDA to approve a vaccine?

A: Once the results are available, the Food and Drug Administration will review the data and either issue an emergency authorization — most likely for specific, high-risk groups of people like health care workers — or a broader approval for commercial licensure. Either way, the agency has said that it will consult with an advisory board of experts before making a decision.

Companies have been in contact with FDA officials all along the way, and many experts predict that the agency will be able to approve an emergency authorization within days, if the results are clear enough.

Q: When will a vaccine be available to any American who wants it?

A: The best-guess range from scientists, investors and federal health officials is the first half of next year.

Even if one of the front-runners gets an answer about its vaccine this year, too few vaccines will have been produced to distribute them widely to the public. The head of Operation Warp Speed, Dr. Moncef Slaoui, told NPR that he estimated about 20 million to 30 million doses of a vaccine would be ready by the end of the year, far short of the 100 million doses that Trump said Wednesday. (The front-runner vaccines all require two doses, given several weeks apart, further complicating the process.)

Slaoui also recently said that Americans would most likely not be widely vaccinated until the middle of 2021, and that the chance of having a vaccine by October or November was “extremely unlikely.”

The first few months of a vaccine’s availability will limit access to high-risk groups like older people or health care workers and police officers.

Peter Lurie, president of the Center for Science in the Public Interest and a former FDA official, said he thought it was not unreasonable to expect that the first batches for high priority groups could be ready by February — “if everything lines up. And the lesson of drug development is that everything hardly ever all lines up.”

Earlier this month, the CDC told public health agencies that 2 million doses of a vaccine might be available by the end of October, with 10 million to 20 million doses possibly available by November, and 20 million to 30 million by the end of December.

In a briefing for reporters Wednesday, officials with Operation Warp Speed described the first few months of a vaccine’s availability as a “constrained” phase when it would be available only to high-priority groups.

Those groups alone include millions of people. At a recent meeting of the Advisory Committee on Immunization Practices of the CDC, an agency official presented a slide showing that in the U.S., there are as many as 20 million health care workers, up to 80 million essential workers and about 53 million people older than 65. Each of those people would need two doses of the vaccine for it to be effective.

For everyone else, the timing depends on the speed of manufacturing and distribution, and a willingness by the public to actually get vaccinated.

In the best-case scenario, additional vaccines could become available to the public early next year. Johnson & Johnson has said it expected to begin late-stage trials of its vaccine this month, and another company, Novavax, could begin its trial soon.

Stéphane Bancel, the chief executive of Moderna, said in an interview Wednesday that he expected a global shortage of vaccines well into next year. “In the first half of next year, at least maybe until Labor Day next year, I anticipate that the world is going to be massively supply-constrained, meaning not enough vaccine to vaccinate everybody,” Bancel said.

And that’s assuming that everyone wants to take a vaccine. Recent polls have shown that is not necessarily the case, especially if the vaccine is seen to have been rushed to market for political reasons.