President Donald Trump makes no secret he would like a COVID-19 vaccine to be available before the election. But it’s doubtful that will happen and, even after a vaccine wins FDA approval, there would be a long wait before it’s time to declare victory over the virus.

Dozens of vaccine candidates are in various testing stages around the world, with 11 in the last stage of preapproval clinical trials — including four in the U.S. One or more may prove safe and effective and enter the market in the coming months. What then?

Here are five things to consider in making vaccine dreams come true.

1. A vaccine is vital in fighting the virus, but it won’t be a quick pass back to our old lives.

Vaccines have helped rid the world of scourges like smallpox, but the process takes time and there are no guarantees. Until clinical trials have been completed on this first round of vaccine candidates, no one knows how effective they might prove to be.

The minimum requirement by the Food and Drug Administration for any COVID-19 vaccine is that it should at least prove 50% effective when compared with a placebo — that is, a neutral saline solution.

By comparison, the annual influenza vaccine ranges between 40% and 60% effective in preventing the illness, depending on the recipient and the season examined. In contrast, a full course of the measles vaccine is about 97% effective.

“It’s very unlikely that a first-generation vaccine will be something like a measles vaccine,” notes Dr. Amesh Adalja, a physician with expertise in infectious diseases and senior scholar at the Johns Hopkins University Center for Health Security.

2. After vaccines gain approval, the real-world evaluation ensues.

Vaccines undergo a protracted testing process involving thousands of subjects. They win FDA approval only after they demonstrate safety and meet at least the minimum standard of effectiveness. Monitoring continues after they hit the market; effectiveness and any rare side effects or safety issues become more apparent after millions of doses are given.

Hypothetically, let’s say the first new COVID vaccines prove 70% effective at preventing the disease. That would mean seven of every 10 people who roll up their sleeves will be protected, but three will not.

While that’s good news for those protected, questions remain about who is covered and who is still vulnerable. It’s possible, Adalja said, that the vaccine would reduce the severity of disease in the remaining three people, thereby helping cut hospitalizations and severe side effects.

But it’s also true that regulators are focused on whether a vaccine prevents disease. Some vaccines can keep you from getting sick without preventing infection, in which case you could still spread the virus even without exhibiting symptoms.

Mysteries remain, at least for now. Scientists don’t know how long the protection will last, for instance. Will protection fade, requiring annual shots, as with influenza? Or will it last for years?

Also, the COVID vaccine candidates are being tested only in adults so far. Most vaccine makers have delayed testing among children or pregnant and breastfeeding women, for example. That could mean an initial lag in safety and efficacy data for those groups, complicating vaccination efforts for children or even front-line health care workers, many of whom are women of childbearing age.

For all those reasons — “if you are looking for a magic wand, you won’t find one in vaccines,” said Dr. William Schaffner, a professor of preventive medicine and infectious disease at Vanderbilt University Medical Center in Nashville, Tennessee. “That said, vaccines will play a substantial role in reducing the epidemic.”

3. After a vaccine is approved, you still may need to wait awhile to get your shot.

Making vaccines is complicated. And so is distributing them. Vaccine makers say they are already producing vaccine in advance of knowing whether they will win approval. But simply having ample vaccine supply doesn’t mean manufacturers will have all the needed glass bottles, syringes or injectors to ship them right away. Indeed, some experts fear that a shortage of both production-line capabilities (special facilities are needed to make vaccines under strict sterile conditions) and limited supplies could hamper distribution of an approved vaccine. Many of the vaccine candidates must be shipped and stored at super-low temperatures, adding to the complexity.

“Even if you have the vaccine, that doesn’t mean you can ship it out. There are multiple, multiple steps, and all of them have to work,” said Dr. Ezekiel Emanuel, a vice provost at the University of Pennsylvania who has warned of potential shortages.

The National Academies of Sciences, Engineering and Medicine have issued a framework for who should get priority for the initial vaccine. State and local health departments will also have a say in how supplies roll out.

Current recommendations say first in line will be health care workers and people with medical conditions that put them at highest risk if they get the virus. People living in nursing homes and other congregate settings will also be higher on the list. Further down are average healthy adults.

Pay attention, and go when it’s your turn, said Schaffner.

“If they say it’s time for people who are middle-aged and have chronic underlying illness such as diabetes, heart disease and lung disease, you have to know what you have and understand it’s your turn,” he said. “You also have to understand if it’s not your turn yet. Be patient.”

Finally, many of the vaccines under consideration will require two doses spaced a few weeks apart, which would add to the delay. If more than one vaccine is approved, which is likely, people will need the second dose to come from the same manufacturer as the first. That could prove a record-keeping nightmare and lead to more delays — depending on how vaccine supplies hold up.

In testimony before Congress in mid-September, CDC Director Robert Redfield said that tens of millions of doses of vaccine may start to become available by late November or December. But the logistics of vaccine distribution means the country won’t be able to return to “regular life” until “late second quarter, third quarter 2021,” Redfield predicted.

4. So don’t throw out your masks yet.

Because any vaccine is likely to fall short of 100% effectiveness and won’t be in widespread distribution for a while, the use of masks and maintaining social distance will be required well into next year, experts say.

“The vaccine will be a start, but we’ll still need to do the things we’ve been discussing throughout — hand hygiene, wearing masks and continuing to remain specifically distant,” said Dr. Krutika Kuppalli, an assistant professor of infectious disease at the Medical University of South Carolina. “Those are the arsenal of tools we will need to use.”

5. What if I don’t want to get vaccinated?

Polls show a good percentage of Americans either don’t want a vaccine or want to wait a bit before getting one. Can they be required to get a shot?

Certain employers, such as hospitals or food production plants, could require their workers to be vaccinated, but a federal mandate is highly unlikely and probably would be unconstitutional, said professor Dorit Rubinstein Reiss, an expert on employer and vaccine law at the University of California-Hastings College of Law.

The likely approach of public health authorities is to educate people about the benefits and potential side effects of a vaccine — down to whether one might experience a sore arm.

“That’s what we do for every vaccine,” said Adalja of Johns Hopkins. A requirement of vaccination for the general public would create resistance and “foster conspiracy theories,” he said.

Most regulation of public health falls to state and local governments and health agencies, Reiss said. States would be “more likely to have narrow or specific mandates that could survive judicial review,” she said.

Schools, of course, require students to be vaccinated against a wide range of illnesses. But a school-age COVID vaccine mandate is doubtful, at least in the near term, because the vaccine hasn’t been tested on school-aged children.

Generally speaking, employers, including the federal government, have the power to require vaccinations, especially if they don’t have a unionized workforce with a contract that might limit their power. All employers, however, face limits set by civil rights and disability laws and may have to provide alternatives for people who can’t or won’t get vaccinated, Reiss said.