The fastest vaccine has taken almost 10-15 years to produced completely. But currently, the scientists are at a race to produce one within a year for the novel Covid-19 outbreak.
Funding for a vaccine has never been greater, with billions of dollars pouring in from around the world to make a product that could help to control the pandemic -- but the US, China and Europe have invested the most.
Dozens of research teams around the world are working to develop a vaccine for SARS-CoV-2, the virus that causes Covid-19, using a mix of established techniques and new technologies, Eliza Mackintosh, Gianluca Mezzofiore and Katie Polglase reported for CNN's special feature.
Before even the most vulnerable groups can get a shot in the arm from their family doctor, however, a lot of work needs to be done -- and a lot of deals need to be made.
The path to a Covid-19 vaccine
Scientists are hoping to deliver a vaccine that protects against Covid-19, and its transmission, by early 2021. In order to do that, the development process has been rapidly accelerated.
Pre-clinical: A vaccine must go through multiple stages before being green lit for use. An initial research and development stage is followed by a series of pre-clinical and clinical trials (consisting of three phases), and typically each step can take two years or more to complete.
Phase 1: In the first stage of clinical trials, the vaccine is given to a small group of people (usually between 10-50) to check it's safe.
Phase 2: Then it's tested on several hundred people to further gauge safety, any potential side effects, the immune response and dosage. But a number of coronavirus vaccines are in simultaneous Phase 1/2 trials, which means they're being tested for the first time on hundreds of people.
Phase 3: In the last stage, scientists give the vaccine to thousands of people across different ages and locations and see how many contract the virus, compared to those who received a placebo. This determines how good it is at reducing new infections -- its efficacy.
Implementation: Regulators then review the trial results to decide whether to approve the vaccine for use, licensing and large-scale manufacturing. Many vaccines also undergo Phase 4 studies after they are approved and licensed.
There are currently 29 vaccines being tested in multiple human trials, running simultaneously around the world. Among these, six vaccines are being tested in seven Phase 3 trials.
Most of the candidates in human trials have either American, European or Chinese financial backing, and some experts believe it will be regulators in one of those places that will be the first to approve a safe and effective vaccine.
American biotechnology firm Moderna was the first in the world to kick off human trials on March 16, just two months after the genetic sequences for SARS-CoV-2 were identified.
Now there are six vaccines in the last stage of human trials (Phase 3) before they seek approval: Three from China, two developed by state-owned Sinopharm and one from private Chinese firm Sinovac Biotech; one from the United Kingdom, produced in partnership between the University of Oxford and AstraZeneca; and two from the US, one by pharmaceutical giant Pfizer, in addition to the candidate by Moderna.
To reach this late stage of trials just six months after discovery is remarkably fast - it would normally take at least six years, according to Professor Adrian Hill, director of the Jenner Institute at Oxford University.
In a bid to get something out as soon as possible, some countries are pushing forward vaccines before their efficacy has been proven in Phase 3 trials.
China has already done it, approving an experimental vaccine for use by its military in late June.
Now Russia is touting a vaccine, despite concerns that corners have been cut in its development. On August 11, President Vladimir Putin announced the registration of a vaccine named Sputnik V, the first in the world to be approved for public use. Russia hasn't released scientific data on its testing, however, and the vaccine was approved the day before the start of Phase 3 trials -- the last and most critical step in the process.
"I hope that the Russians have actually, definitively proven that the vaccine is safe and effective. I seriously doubt that they've done that," Dr Anthony Fauci, the director of the US National Institute of Allergy and Infectious Diseases, told ABC News' Deborah Roberts.
When Americans hear announcements from countries like Russia or China about vaccine development, Fauci said they should remember that the US has very different standards in place.
While that sort of fast-tracking won't happen in the US or Europe -- where regulators require the full complement of safety and efficacy tests -- several drug companies are pressing ahead and producing stockpiles in case their vaccines get the go-ahead.
AstraZeneca has said it reached agreements with several governments -- including the US and UK - and other organizations to produce at least 2 billion doses of vaccine, with the first deliveries starting as early as September.
The Biomedical Advanced Research and Development Authority (BARDA), a branch of the US Department of Health and Human Services, is injecting billions of dollars into companies to ramp up vaccine development and manufacturing, including AstraZeneca. It has also inked deals for doses with Novavax, Pfizer-BioNTech, Johnson & Johnson, Moderna and Sanofi and GSK's joint effort.
This speed is one of the reasons many citizens are wary of getting vaccinated. A recent CNN poll found only 66% of Americans would get a Covid-19 vaccine should one become available.
And, even if everyone does take the vaccine, it almost certainly won't be 100% effective.
Many vaccines are not even close to 100% effective. For example, the world's first malaria vaccine — RTS,S or Mosquirix -- was rolled out across Africa last year, despite offering only 39% protection against malaria in children aged 5-17 months. This was considered to be worth it in countries with high rates of the disease when used alongside other interventions.
In comparison, the US Food and Drug Administration has said that a coronavirus vaccine would have to protect at least 50% of vaccinated people to be considered effective. It's thought that level of efficacy can help stop transmission, especially in combination with other treatments and prevention measures.
Some experts believe that the virus will never really go away and that it may instead become a typical, more manageable infection like influenza.
"This sense that when the vaccine comes, it will be over … it's a dangerous promise," said Heidi Tworek, a health communications expert at the University of British Columbia. "The truth is, we've only ever eliminated one disease through vaccines, and that was smallpox and it took hundreds of years."
But countries have released extensive funds to fill the void.
The US has already allocated more than $1.5 billion for domestic manufacturing and distribution in order to ensure a vaccine can be produced to scale.
The rush to secure supplies is inflaming geopolitical issues too.
The World Health Organization (WHO) has encouraged countries to cooperate in order to ensure fair global access, but some experts believe national interests will get in the way.
Robinson says a precedent was set during the 2009 H1N1 influenza pandemic, also known as swine flu, which the CDC estimates killed as many as 575,000 people worldwide (31 times more than numbers reported by WHO). When a vaccine became available, wealthier countries bought up the supplies, leaving poorer nations at the back of the line, according to WHO and public health experts.
"Many countries closed their borders for exporting vaccines until their own needs were met," explained Robinson, who was involved in the US response.
Fortunately that strain of H1N1 was much milder than experts had predicted and some older populations showed some immunity to it, meaning the vaccine didn't play a key role in ending the pandemic.
But Covid-19 is in a different league and is showing no signs of a natural decline.
In the hopes of avoiding a repeat of what happened in 2009, WHO launched the Access to Covid-19 Tools' (ACT) Accelerator on April 24 in which countries agree to ensure "all people have access to all the tools to prevent, detect, treat, and defeat Covid-19." But the US and China didn't sign it.
Just over a month later, President Donald Trump announced America's withdrawal from WHO.