Many wary parents say they plan to hold off signing up their young children for Covid-19 vaccinations, just as health authorities are preparing to deliver the shots in the coming days.

The parents’ fears pose a major obstacle for the U.S. vaccination campaign, which authorities have been seeking to expand in an effort to move past the pandemic, even as people return indoors for the winter.

Later...

Many wary parents say they plan to hold off signing up their young children for Covid-19 vaccinations, just as health authorities are preparing to deliver the shots in the coming days.

The parents’ fears pose a major obstacle for the U.S. vaccination campaign, which authorities have been seeking to expand in an effort to move past the pandemic, even as people return indoors for the winter.

Later this week, doctors, nurses and pharmacists could start administering the Covid-19 vaccine from Pfizer Inc. and BioNTech SE, which federal health regulators recently authorized for use in young children ages 5 to 11 years.

While a large number of parents have expressed eagerness to vaccinate their young children as soon as possible, many others say they will wait, out of concerns the inoculations could have unexpected or long-term side effects, affect fertility, or were too rushed.

Cherish Latting, of Roxie, Miss., with her family. She is waiting before signing up her 9-year-old daughter for the Covid-19 vaccine.

Photo: Cyndi McCaleb

“It’s kind of like an iPhone; you always wait and see how the bugs are,” said Cherish Latting, 36, a bar manager in Roxie, Miss.

Ms. Latting said she is vaccinated, along with two of her teenage sons. Yet she said she would wait and see that the vaccines aren’t causing side effects before signing up her 9-year-old daughter.

There are 28 million 5- to 11-year-olds in the U.S. Covid-19 infections are usually mild in children, according to doctors, though some can become serious—in rare cases, leading to hospitalization and even death.

Health authorities want to vaccinate the youths to protect them and to limit their ability to spread the virus to more vulnerable older people. The drive to vaccinate the youngsters is expected to start in some places as soon as Wednesday, after the Centers for Disease Control and Prevention signed off Tuesday night.

As the FDA nears a decision on authorizing Pfizer’s Covid-19 vaccine for children 5-11 years old, public-health officials and pediatricians are sharing research with families to assure hesitant parents of the shot's safety. Photo: John Locher/Associated Press The Wall Street Journal Interactive Edition

A CDC advisory panel voted unanimously in support of the vaccines. The CDC had been waiting for the vote before issuing its own recommendation.

Shots will begin arriving at vaccination sites in the coming days, and some inoculations could begin as soon as Wednesday.

The campaign should be running at full capacity next week, said White House Covid-19 coordinator Jeff Zients.

Parents will be able to search a federal website—vaccines.gov—to find a vaccination site and sign up their children for a spot, Mr. Zients said.

Some 27% of parents who were recently polled said they would vaccinate their 5- to 11-year-olds right away, while 33% said they would wait and see, and 5% said they would go ahead only if their child’s school requires vaccination, according to a survey of 1,519 people, including 219 parents of 5- to 11-year-olds, by the Kaiser Family Foundation. About 30% said they wouldn’t vaccinate their children at all.

Samantha Golembo, who has 2-year-old twins and a 5-year-old son, said she won’t get him vaccinated unless his school requires it.

Photo: Samantha Golembo

More than 70% of the polled parents said they were very or somewhat concerned that not enough is known about long-term side effects, or their children might experience serious side effects. Two-thirds of parents in the Kaiser survey said they were concerned the vaccines would hurt their child’s fertility in the future.

The CDC has said there is no evidence that Covid-19 vaccines cause fertility problems. But the concern continues to circulate, though its provenance is unclear.

Citing fertility and other concerns of long-term side effects, Samantha Golembo, a 30-year-old from Brooklyn who has 2-year-old twins and a 5-year-old son, said she won’t get him vaccinated unless his school requires it.

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Ms. Golembo said she got vaccinated because the nursing home where she works required it. She also expressed concern about the shot’s rapid development.

“I am pro-vaccine, my kids are up-to-date with vaccines—it’s just the simple fact of this vaccine being so rushed,” she said.

Pediatricians and immunologists say the benefits of vaccinating young children outweigh the risks.

Covid-19 is the eighth leading cause of death in children, killing more than 700 under the age of 18 years since the start of the pandemic, according to the CDC. The deaths are largely vaccine-preventable, pediatricians said.

The Pfizer-BioNTech vaccine was found to be safe and 90.7% effective in a clinical trial, according to the Food and Drug Administration. Side effects in children were similar to those in adults and adolescents, including injection site pain, headaches, chills, fever and fatigue, the agency said.

Children ages 12 and older who got their Covid-19 vaccine at the Philadelphia Zoo in September, completed a 15-minute watch period near the bats exhibit.

Photo: rachel wisniewski/Reuters

Researchers plan to monitor vaccinated children in the trial for long-term side effects.

It is rare that side effects that haven’t appeared in adults or adolescents would appear in younger children, said Yvonne Maldonado, a professor of pediatrics and infectious disease at Stanford University. The older age groups are a good model to understand how the vaccines work.

The way the vaccine works—delivering messenger RNA that disintegrates relatively quickly after it is injected into the body—also suggests a low risk for long-term side effects, Dr. Maldonado said.

“We really have a wealth of data to show how effective and safe” the vaccine is, said Todd Wolynn, a pediatrician and chief executive officer of Kids Plus Pediatrics in Pittsburgh.

Like many other parents, Ms. Latting in Mississippi said she was concerned about myocarditis, an inflammatory heart condition, after reviewing a pamphlet about it when her sons were vaccinated.

Myocarditis has occurred in small numbers of people, especially teenage and young adult males, who have taken messenger RNA vaccines like Pfizer-BioNTech’s.

No cases of myocarditis were found in the key study testing the Pfizer-BioNTech vaccine in 5- to 11-year-olds, but the study was considered too small to detect the potential risk.

The risk of myocarditis is low and cases that have come up have largely been mild and resolved quickly, according to studies. The risk of myocarditis after Covid-19 infection is much higher, according to several studies.

—Sabrina Siddiqui contributed to this article.

Write to Felicia Schwartz at felicia.schwartz@wsj.com