WASHINGTON (BLOOMBERG) - Led by the US, the world has hit a frightening Covid-19 threshold, with two million people dead and few expectations for the numbers to start dropping any time soon.

"You want to get to the point first where the virus can't outrace you," said Gregg Gonsalves, an epidemiologist at the Yale School of Public Health and co-director of the Global Health Justice Partnership.

"It's very hard to project out in any fine level of resolution how many people will be dead from this, in even six months to a year."

With the rollout of the Pfizer-BioNTech vaccine and the Moderna shot going slowly in the US - and virtually non-existent in many parts of the world - the odds of controlling the outbreak before the summer at the earliest are slim, especially because it can take weeks for an infected person to die.

"We have a great forest fire of a pandemic happening," Gonsalves said in a phone interview. "But if you have just a bucket of water in a forest fire, then you aren't doing well."

Overall, the US is leading all countries in deaths with 388,705, with Brazil, India, Mexico and Britain next in line.

Covid-19, meanwhile, has already killed more people than malaria and tuberculosis combined in the past year, and is nearing the peak number of annual deaths seen from Aids, which occurred in 2005.

French Prime Minister Jean Castex sees a gradual exit from the pandemic in his country, potentially by next summer.

"This tragedy our country is living, that the world has been living for months and which weighs on so many of us, the utmost priority to get out of this crisis is the recourse to vaccination," Castex said on Thursday at a news conference in Paris.

"But we must collectively show patience and responsibility, because it will be several months before vaccination will be able to sufficiently protect us."

In the US, public health officials say that most people will have access to the vaccine by summer, which will start to choke off the virus and create some level of protection.

Ali Mokdad is a population scientist and professor of global health at the University of Washington, where the Institute for Health Metrics and Evaluation (IHME) has been tracking and modelling the outbreak for the past year.

The institute projects that the world won't get to about three million deaths by the end of 2021, meaning that fewer than one million people will die from coronavirus this year.

The group's latest analysis projects 2.89 million deaths worldwide by the end of the year.

"All the way to December, it's not going to be another million," Mokdad said in a telephone interview. When it comes to infections, he said, "we are not going to see any more situations in the US with 4,000 deaths a day."

People need to wear masks until 75 per cent of the population is immunised, Mokdad said, which could happen sometime this summer.

That assumes, he said, that the vaccines continue to roll out, that no further side effects emerge, that there is no new mutation that makes it less effective and that Americans don't start to celebrate too soon.

"Cases are going to come down simply because of the vaccine and the weather," he said. "It's on us to keep doing what we need to do."

Still, studies have not confirmed whether the vaccine will stop the spread of the virus itself, instead showing it protects those who receive it from contracting a symptomatic or severe infection.

As more and more people obtain some protection against the immediate ravages of the pathogen, the death and hospitalisation rates should start to slow.

Gonsalves, though, is concerned that even if the US is able to stem its outbreak, the virus will continue to surge elsewhere.

"If you can't put it out everywhere," he said, "you can't put it out anywhere. You are always going to have travel seeding new outbreaks."

Booster shot

While the vaccines authorised for emergency use in the US are promising to protect people right now, it also remains unclear how long that protection will last.

Pfizer is continuing to study its vaccine, hoping to move from its emergency use authorisation to final approval, and to determine if regular booster shoots will be needed to keep the virus from re-emerging.

While the number of deaths is likely to recede as more and more people get vaccinated, herd immunity - which occurs when a large portion of a community becomes immune to a disease, making the person-to-person spread unlikely - won't be achieved until at least 70 per cent of the population is protected, experts including Anthony Fauci have said.

IHME projects this to happen sometime in July.

Fauci, the top US infectious disease doctor and soon to be a key adviser to Joe Biden once he becomes US president on Jan 20, said last month that herd immunity will likely happen in the summer, with a return to normality by the end of the year.

Meanwhile, the World Health Organisation puts the timeline globally at 2022.

Worldwide protection

"Even as vaccines start protecting the most vulnerable, we're not going to achieve any levels of population immunity or herd immunity in 2021," said the WHO's chief scientist, Soumya Swaminathan at a Jan 11 news briefing.

"Even if it happens in a couple of pockets, in a few countries, it's not going to protect people across the world."

The WHO has placed orders for more than two billion vaccine doses for low and moderate income countries through its Covax facility, designed to fight the pandemic. It also has the option to acquire a billion more, according to Bruce Aylward, a Canadian epidemiologist working with the WHO.

"This issue is not the lack of vaccines that we are ordering for the low and low middle income countries," according to Aylward. "The crucial thing is the timing, to get at least some of those doses early enough to protect these health care workers on the front lines in these countries, as well as the older populations and others who are at high risk of potentially dying of this disease."

Aylward urged wealthier countries to focus not on making sure that all of their population is vaccinated first, but that those at highest risk and most likely to keep the virus viable worldwide get priority access.

'Incredible progress'

"This is not the time to get disheartened," said the WHO's Swaminathan, an Indian pediatrician known for her work on tuberculosis and HIV.

"We've made incredible progress, and a year ago nobody would have predicted that there would have been not one but several vaccines against this new virus that have been developed, manufactured, produced and distributed."

It takes time to scale up the production of doses "not just in the millions but here we're talking about the billions," she said.

"We have to be a little bit patient."