20% of all new US COVID-19 cases in last week of April were children, data shows

According to a report by the American Academy of Pediatrics (AAP) published last month, children represented 22.4% of new COVID-19 cases between April 22 through April 29 in the United States.

During that time, children also made up 1.2% to 3.1% of reported hospitalizations related to the novel coronavirus. 

In a previous report from the U.S. Centers for Disease Control and Prevention published in January, researchers indicated that while children are susceptible to COVID-19 infections, they tend to have a lower incidence and fewer severe forms of the disease than adults. The report also noted that COVID-19 cases in children, adolescents, and young adults have increased since the summer of 2020. 

However, the recent data from the AAP illustrates the need to vaccinate young people amid the increase in recent weeks.

Medical experts say the recent increase in cases among children could be due to the continued spread of the novel coronavirus variant first identified in the U.K. that appears to infect children more easily than previous strains. 

"Please understand, this B.1.1.7 variant is a brand new ballgame," Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy, said last month on "Meet the Press."

Osterholm said in Minnesota there have been 749 schools with reported cases of the more contagious variant over the last two weeks. Across the U.S., many children have returned to the classroom after spending much of the last year online.

RELATED: UK variant a 'brand new ballgame,' infecting children in US 'very readily,' epidemiologist warns

In Italy, the B.1.1.7 variant is also prevalent among infected schoolchildren and is helping to fuel a "robust" uptick in the curve of COVID-19 contagion in the country, the country’s health minister said last in March. 

The CDC previously noted in a separate report that young adults aged 18 to 24 represented the highest case rates of the novel coronavirus in the U.S.

Between Mar. 1 through December 2020, adults aged 18-24 made up 57.4% of COVID-19 cases between Mar. 1 and Dec. 12, 2020, according to the CDC.

Another concerning factor regarding children and COVID-19 was linked to a rare inflammatory syndrome related to COVID-19 that was on the rise across the nation. In August, the CDC reported that nearly 600 children had been hospitalized in the United States with multisystem inflammatory syndrome in children, or MIS-C.

MIS-C is a condition that causes various parts of the human body to become inflamed, including the heart, lungs, kidneys, brain, skin, eyes, or gastrointestinal organs, according to the CDC. 

The agency says the number of MIS-C cases in the U.S. surpassed 1,000 as of Oct. 1, 2020. By Feb. 1, the number had topped 2,000.

RELATED: Moderna says its COVID-19 vaccine appears safe, 96% effective in teens 12-17

Another study by CDC published April 6 in JAMA Pediatrics found that most children with the serious inflammatory illness linked to the coronavirus had initial COVID-19 infections with no symptoms or only mild ones.

MIS-C tends to be milder in kids who were sicker with COVID-19, although more than half of affected youngsters received intensive hospital care, according to the CDC analysis.

The study represented the largest analysis to date on U.S. cases of MIS-C and bolsters evidence that it is a delayed immune response to COVID-19. The study included almost 1,800 cases reported to the CDC from March 2020 through mid-January. Most were in kids younger than 15 but the study included up to age 20.

Upticks in cases have occurred two to five weeks after COVID-19 peaks and have followed the spread of initial infections from urban to rural areas, the researchers said. More recent CDC data indicate there’s another emerging peak in the pediatric condition consistent with that trend.

State-reported cases through March 29 totaled 3,185 and included 36 deaths, the CDC’s website shows. State reports aren’t always timely so it is uncertain how many U.S. children developed the illness since the study ended.

RELATED: MIS-C: Cases of rare inflammatory syndrome linked to COVID-19 on the rise among children in US

Most kids who had COVID-19 don’t develop the post-infection illness. Almost 3.5 million U.S. children and teens have tested positive for COVID-19, according to data compiled by the AAP and the Children’s Hospital Association.

The condition was first reported in Europe in late winter and spring of last year. Some cases, especially those that follow silent, undiagnosed COVID-19 infections, may be mistaken for Kawasaki disease, a rare condition that can cause red skin, swelling and heart problems.

However, medical experts are hoping that extending vaccinations to children will drive down the nation’s caseload even further than what it is today. 

Moderna announced on Thursday that data from an ongoing trial of its COVID-19 vaccine for teens ages 12 to 17 was 96% effective against the novel coronavirus. No additional side effects or serious safety concerns were reported so far, according to the company. 

The trial consists of 3,235 teenagers, and efficacy for the vaccine was approximately 96% for the participants who received at least one injection, Moderna reported. The company also said that because the incidence rate of COVID-19 was lower in adolescents and teenagers, the vaccine’s effectiveness on the trial patients is mainly against milder symptoms of the disease. 

The U.S. Food and Drug Administration is also expected to authorize Pfizer’s vaccine for young people by next week, setting up shots for many before the beginning of the next school year. The announcement comes barely a month after the company found that its shot, which is already authorized for those age 16 and older, also provided protection for the younger group.

President Joe Biden said Tuesday that if the FDA authorizes the use of Pfizer's vaccine in children, the administration is prepared to ship doses to 20,000 pharmacies around the country and directly to pediatricians.

Pfizer in late March released preliminary results from a vaccine study of 2,260 U.S. volunteers ages 12 to 15 showing there were no cases of COVID-19 among fully vaccinated adolescents, compared with 18 cases among those given dummy shots.

Meanwhile, in Canada, health officials approved Pfizer’s COVID-19 vaccine Wednesday for children as young as 12.

Dr. Supriya Sharma, the chief medical adviser at Health Canada, confirmed the decision for ages 12 to 15 and said it will help children return to a normal life. Canada is the first country to authorize Pfizer for that age group. The European Union is also reviewing it.

Kelly Hayes and The Associated Press contributed to this story.