Young, healthy people should be prepared to wait more than a year to be vaccinated against the coronavirus, the World Health Organization’s chief scientist said Wednesday.

Many people are under the misconception that they’ll be able to get a vaccine in early 2021, “and then things will be back to normal,” Soumya Swaminathan said in a question-and-answer session broadcast on YouTube.

In reality, she said, any vaccine that is ready next year will be available in limited quantities, with health-care workers and others on the front lines having first priority, followed by “the elderly and so on.”

“There will be a lot of guidance coming out, but I think an average person, a healthy young person, might have to wait until 2022 to get a vaccine,” she predicted.

Although young people can get sick and die of COVID-19, the disease caused by the coronavirus, and can spread the virus to others, some evidence suggests they are less likely to suffer serious complications than older people or those with health problems.

With an unprecedented global demand for a vaccine, governments will have to work so that people most at risk get immunized first. By 2022, it is hoped that mortality rates will have dropped and the most vulnerable people will be protected, Swaminathan said Thursday.

Swaminathan reiterated the WHO’s stance against allowing the virus to spread unchecked in an effort to reach herd immunity, emphasizing that the concept should be discussed only within the context of a vaccine.

“Once we have a vaccine, we can aim to have population immunity – herd immunity – because you’ll need to vaccinate at least 70 percent of people, have them protected, to really break the transmission,” she said.

More than 150 countries have joined the WHO’s Covax initiative, a cooperative arrangement in which nations combine forces to invest in vaccine development and agree to allocate the first doses based on population and then by level of risk.

The initiative has said its goal is to have 2 billion doses of safe vaccines to deliver by the end of 2021 – a goal that could mean one dose for roughly a quarter of the world.

The United States has not joined the program, meaning that the U.S. timeline for vaccine distribution may differ from the one laid out by the WHO.

However, in an updated document released Tuesday, the U.S. Centers for Disease Control and Prevention said that with limited supplies, it may ask some groups of people to not get the vaccine at first. It said it was working on a way to “distribute these limited vaccines in a fair, ethical, and transparent way.”

The CDC also said that a COVID-19 vaccine may not be recommended for children when it first becomes available in the U.S. because the vaccine has not been tested on them.

“Only non-pregnant adults” have participated in early trials so far, the CDC said on its website. “However, clinical trials continue to expand those recruited to participate. The groups recommended to receive the vaccines could change in the future.”

In a draft document framework released last month, the National Academies of Sciences, Engineering and Medicine said only 10 million to 15 million doses of a vaccine may be available initially, which may cover only 3 to 5 percent of the U.S. population.