More than four months after the start of the coronavirus pandemic, how close is the United States and the world to a safe and effective vaccine? Scientists say they are seeing steady progress and express cautious optimism that a vaccine will be ready in the spring.

As of early July, around 160 vaccine projects were underway around the world, according to the World Health Organization.

Typically, a vaccine trial has several phases. In an initial phase, the vaccine is administered to 20 to 100 healthy volunteers. The goal of this phase is to make sure the vaccine is safe and to note any side effects.

In the second phase, there are hundreds of volunteers. In addition to monitoring safety, researchers are trying to determine if the injections produce an immune system response.

The third phase concerns thousands of patients. This phase continues the goals of the first two, but adds a focus on the vaccine’s effectiveness in protecting people exposed to the pathogen, in this case, the coronavirus. This phase also collects data on more unusual negative side effects.

Under ordinary circumstances, these phases last for years. But for the coronavirus, the schedule is shortened. This has spurred more public-private partnerships and significantly increased funding.

Here is an overview of the most advanced vaccine candidates in clinical phases:

The three most advanced vaccine candidates are in phase 3.

One is to be developed by researchers at the University of Oxford in the UK He uses a weakened version of a virus that causes the common cold in chimpanzees. The researchers then added proteins, called antigens, from the new coronavirus, in the hopes that these could trigger the human immune system to fight off the virus once it encounters it.

Another candidate in a phase 3 trial is under development in China. It uses a killed, and therefore safe, version of the novel coronavirus to trigger an immune response.

And on July 15, biotech company Moderna, which is partnering with the National Institutes of Health, announced it would move to Phase 3 within two weeks.

Two more have reached phase 2, while eight more are completing their phase 1 trials while also starting phase 2 trials.

These candidates are developed by a mix of companies and institutions in several countries. These efforts aim to take advantage of a range of technologies.

RNA material is used which provides instructions to a body to produce the necessary antigens on its own. This is a relatively untested vaccination approach, but if it works, it has aspects that could make it easier to manufacture. Another approach is similar, but uses DNA instead of RNA.

A US biotech company, Novavax, is receiving federal funding to produce a vaccine that uses a protein made in the lab to inspire an immune response.

Beyond these, 10 other candidate vaccines are in phase 1 clinical trials, while 140 have not yet reached the clinical phase.

Having so many potential vaccines at this point is impressive, experts say, given how little time scientists know about the new coronavirus.

“Overall, the pace of the development and advancement of the Phase 3 trials is impressive,” said Matthew B. Laurens, associate professor in the Center for Vaccine Development and Global Health at the University’s Faculty of Medicine. from Maryland. “The public-private partnerships have been very successful and meet the goals of rapid vaccine development.”

Also, the fact that several types of vaccine approaches are being tested means that we don’t put all of our eggs in one basket.

“We will need multiple applicants if any of these items are having difficulty manufacturing or showing a safety signal when implemented in more people,” Laurens said.

Meanwhile, at a time of growing public skepticism about government and vaccines, the Food and Drug Administration recently issued additional guidance on vaccine effectiveness. The new guidelines require vaccines to prevent or reduce the severity of the disease at least 50% of the time if they are to gain agency approval.

The FDA guidelines “reaffirmed the FDA’s very rigorous process for approving any vaccine. It gives great assurance that this was going to be addressed by the book, ”said William Schaffner, professor of preventive medicine and infectious diseases at Vanderbilt University Medical Center. “The more we talk about getting things done quickly, the more people think, ‘They’re probably cutting corners.’

How quickly will we have access to a viable vaccine?

In early April, Kathleen M. Neuzil, director of the University of Maryland vaccination center, said PolitiFact that if all went well, there could be five or six vaccines on trial within six months. Now, three and a half months later, there are two to three times more.

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, and other officials have remained consistent in their estimate of the timing: 12 to 18 months after the start of the pandemic, or roughly the end of spring 2021 .

Schaffner told PolitiFact he continues to view the first quarter of 2021 as a reasonable goal. “I think that’s where the needle points,” he says.

It remains to be seen how quickly vaccines can be manufactured and distributed once approved for general use. Civil servants are also battling which Americans will have access first. It is therefore not known how long a person should wait to be vaccinated.

Laurens said he wasn’t too concerned with the cast, as it’s something officials have had a long history of. “Well-established programs exist for the distribution of vaccines, including the seasonal vaccination of large numbers of individuals,” he said.

Another encouraging sign, Schaffner said, is that the coronavirus itself appears to be relatively stable. There were concerns that the novel coronavirus, like many other viruses, could be mutant over time. If the virus changes enough, it could become a problem plaguing vaccine researchers.

But so far that has not happened. Even if there is evidence that mutations make the virus more transmissible, or that a new variant makes people sicker, it should not affect the vaccination process. “The central core of the virus would remain the same,” Schaffner said.

Over the past month, there has been relatively little news about the progress made on some vaccines. Schaffner is not worried about the relative calm.

“In a vaccine trial, if there is an unfavorable safety result, the guillotine goes down and that trial is stopped,” he said. “So quiet that’s good, because we would know if something bad happened.”