U.S. leading infectious disease expert Dr. Anthony Fauci said parents should “vaccinate the children,” noting that unvaccinated young people are “vehicles of spread” and are at risk of serious long-term infection.

Fauci spoke during a lecture at the U.K.’s London School of Hygiene and Tropical Medicine on Wednesday, citing the importance of vaccinating children especially as they start fall classes. He also discussed the importance of booster shots and the impact of “long Covid.”

“We don’t know what the effects are going to be on anyone, including children. So, it may be that much to our dismay that children who get infected have long-term consequences that we don’t fully appreciate right now,” Fauci said.

He added that “for those reasons, one of transmissibility, one of the seriousness of disease and one of uncertainty about long-range consequences, I come down strongly on ultimately vaccinating our children.”

Many schools have been battling through the national debate on whether to require students to wear masks. Some U.S. states have issued bans on mask mandates and are now under investigation by the Department of Education for civil rights violations.

Since schools reopened in the U.S., a record number of nearly 252,000 children tested positive for COVID-19.

“We are almost overrun. We have a lot of children in hospitals now,” Fauci said at the lecture. “So, even though relatively speaking, compared to an adult they don't get as seriously ill, we have lost more children from SARS-CoV-2 than we ever lose to influenza.”

CNBC noted that many health officials fear that if children do not get vaccinated and COVID safety protocols like mask wearing are not enforced in schools, COVID hospitalizations could get even worse.

Though vaccines are still not recommended for those under the age of 12, the U.K. has yet to allow those under 15 to get vaccinated.

Last month, the U.K.’s Joint Committee on Vaccination and Immunisation said, “the margin of benefit is considered too small to support universal vaccination of healthy 12- to 15-year-olds at this time.”

This move contradicts the recommendations of many other countries that have already been administering COVID-19 vaccines for healthy 12- to 15-year-olds. Those countries include the U.S., Canada, China, Japan, Singapore, Israel, the UAE and other countries in Europe.