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Countries are racing to immunize adults against Covid-19 and move toward a more normal future. To achieve the vaccination rates that health authorities are aiming for, the shots must eventually reach the arms of children and teenagers, too.

Children aren’t going to be vaccinated for several months at least, however, because drugmakers are still testing shots in younger ages.

That means health authorities can’t be confident of securing community protection against the virus, known as herd immunity, until later this year at the earliest, because children under 18 make up a significant proportion of many countries’ populations.

“We definitely need to get kids vaccinated if we want to be as close to normal as we can," said Octavio Ramilo, chief of infectious diseases at Nationwide Children’s Hospital, in Ohio.

As governments push to move past the pandemic, vaccinating children is emerging as a key obstacle, along with initially limited supplies of vaccines.

Researchers say between 70% and 85% of a population would need to be protected through infection or vaccination to achieve herd immunity, the point when so many people are immune that the virus has nowhere to go and even those who aren’t immune have protection.

“It’s hard to do that just in terms of numbers if you’re not going to vaccinate kids," said Adam Ratner, chief of pediatric infectious diseases at Hassenfeld Children’s Hospital in New York.

Children and adolescents make up 22% of the U.S. population, according to the Census Bureau’s latest projections, and 18% of the population of the European Union.

Drugmakers first tested Covid-19 vaccines in older ages. As a result, the shots have been authorized only for the oldest teenagers and adults so far.

The shot from Pfizer Inc. and partner BioNTech SE is cleared in the U.S. for people 16 years and older, while vaccines from Moderna Inc. and Johnson & Johnson for 18 years and up. A vaccine from AstraZeneca PLC and the University of Oxford is in use in the U.K. and EU for ages 18 and over.

Pfizer has enrolled more than 2,000 children from ages 12 to 15 years in one study and expects to submit the data from that study to the U.S. Food and Drug Administration in weeks. The FDA could authorize use by the fall, Pfizer Chief Executive Albert Bourla said at The Wall Street Journal’s Health Forum on Tuesday.

Pfizer said Thursday it had begun evaluating its vaccine in children 6 months to 11 years.

Moderna is aiming to have its vaccine available for adolescents before the start of the 2021 school year and recently launched another trial with children as young as six months.

The University of Oxford is enrolling children ages 6 to 17 years in a trial of the vaccine it co-developed with AstraZeneca.

Clinical trials to assess the safety and efficacy of vaccines in children that have already been cleared for adult use can be done more quickly than the large-scale studies in adults that have already taken place.

The adult trials enrolled tens of thousands of volunteers, who were randomly selected to receive either the vaccine or a placebo. Researchers were then able to compare rates of infection and illness in each group months later to determine how much protection the vaccine provides.

For the adolescent and children’s trials, the focus is more on safety and measuring the immune response of the young volunteers with a blood test.

If researchers find the children in the study had a similar immune response as adults did, then the efficacy of the vaccines will likely be similar as well, said Robert Frenck, principal investigator for the Pfizer Covid-19 vaccine clinical trial at Cincinnati Children’s Hospital Medical Center and director of its vaccine research center.

Vaccines probably won’t be ready for use in younger children until early 2022, health experts said, in part because researchers need to test lower doses.

“The dose is not such a big leap to go from adults to teens," said Katherine Luzuriaga, a pediatric infectious disease physician and the lead investigator of Moderna’s adolescent trial at the University of Massachusetts Medical School site. “Once we start going into the younger age groups, there’s a bit more work to determine the appropriate doses."

Vaccinating those at most risk of severe illness and death has been the first priority of vaccination drives. In most countries, that has meant giving priority to elderly citizens and those with conditions that heighten their risk of severe Covid-19.

The rate of hospitalization is 35 times as high, and the death rate is 1,100 times as high, among people 65 to 74 years old infected with Covid-19, compared with children ages 5 to 17, according to the U.S. Centers for Disease Control and Prevention.

Health authorities say children don’t need to be vaccinated to start resuming certain activities like in-person learning at schools that are taking precautionary measures. Some experts caution against focusing too heavily on a specific herd immunity target, as building up population-level protection is an incremental process.

Children infected with Covid-19 overwhelmingly experience mild symptoms but can still get seriously ill on rare occasions and are able to transmit the virus to others.

More than 13,500 children have been hospitalized with Covid-19 infections in the U.S. alone, and more than 260 have died, according to a March 18 report from the American Academy of Pediatrics and the Children’s Hospital Association.

This story has been published from a wire agency feed without modifications to the text.

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