The European Union’s drug regulator approved Pfizer’s coronavirus vaccine for use on children aged 5 to 11, paving the way for shots to be given to millions of elementary school students amid a new wave of infections sweeping the continent.

The European Medicines Agency has approved a COVID-19 vaccine for use in young children for the first time.

The agency “recommended granting an extension of indication for the COVID-19 vaccine Comirnaty to include use in children aged 5 to 11,” according to the statement.

The EMA estimated that the vaccine was about 90% effective in preventing symptomatic COVID-19 in young children after evaluating a study of more than 2,000 children, and that the most common side effects were pain at the injection site, headaches, muscle pain, and chills. The two-dose regimen, according to the agency, should be given to children three weeks apart.

At least one country dealing with an increase in infections did not wait for the EMA’s approval. Authorities in Vienna, Austria’s capital, have already begun vaccinating children aged 5 to 11. Europe is currently at the epicenter of the pandemic, and the World Health Organization has warned that unless immediate action is taken, the continent’s death toll could exceed 2 million by the spring.

Before health authorities in member countries can begin administering shots, the EMA green light for the vaccine developed by Pfizer and German company BioNTech must be rubber-stamped by the EU’s executive branch, the European Commission.

Jens Spahn, Germany’s health minister, announced earlier this week that shipping of vaccines for younger children in the EU would begin on December 20.

Pfizer’s kids-sized shots were approved by the US earlier this month, and other countries, including Canada, followed suit.

Pfizer tested a dose for elementary school-age children that is one-third the amount given to adults. Dr. Bill Gruber, a Pfizer senior vice president, stated in September that even with the smaller shot, children aged 5 to 11 years old developed coronavirus-fighting antibody levels that were just as high as teenagers and young adults who received the regular-strength shots.

However, the studies on Pfizer’s vaccine in children were not large enough to detect any rare side effects from the second dose, such as the chest and heart inflammation seen in mostly male older teens and young adults.

Officials in the United States noted that COVID-19 has killed more children aged 5 to 11 than other diseases, such as chickenpox, did before children were routinely vaccinated.

The EMA announced earlier this month that it had begun evaluating the use of Moderna’s COVID-19 vaccine for children aged 6 to 11; a decision was expected within two months.

Although most children only experience mild symptoms from COVID-19, some public health experts believe that immunizing them should be a priority in order to reduce the virus’s continued spread, which could theoretically result in the emergence of a dangerous new variant.

Researchers disagree on the extent to which children influenced the course of the pandemic. Early research indicated that they did not play a significant role in viral spread. However, some experts believe that children played a significant role in spreading contagious variants such as alpha and delta this year.

The World Health Organization said this week that because children and teenagers have milder COVID-19 disease than adults, “it is less urgent to vaccinate them than older people, those with chronic health conditions, and health workers.”

It has asked rich countries to stop immunizing children and to immediately donate their doses to poor countries that have yet to give their health workers and vulnerable populations a first vaccine dose.

Nonetheless, WHO acknowledged that there are advantages to immunizing children and adolescents that go beyond the immediate health benefits.

“Vaccination that reduces COVID transmission in this age group may reduce transmission from children and adolescents to older adults and may help reduce the need for mitigation measures in schools,” according to the WHO.