Kindergartner Grace Truax, 5, removes her mask before posing for a portrait during "picture day" at Rogers International School on September 23, 2020 in Stamford, Connecticut.
  • Covid-19 vaccines haven't been authorised for children under age 12 yet.
  • That means kids are at higher risk of contracting Delta, the most transmissible variant to date.
  • But experts are more worried about kids spreading the variant than getting severely ill themselves.
  • For more stories visit Business Insider.

The best way to protect yourself from the Delta variant? Get vaccinated.

But that's not an option for millions of children under 12. So for the time being, children are at high risk of acquiring a Delta infection.

"The fact that we're seeing outbreaks in certain parts of the country [US] specifically in children is because, at this moment, those are the most vulnerable hosts because they're not vaccinated," Erlinda Ulloa, a paediatric infectious-disease specialist at the University of California, Irvine, told Insider.

Delta is the most transmissible coronavirus variant to date. An analysis from Public Health England found that it's associated with a 60% increased risk of household transmission compared to Alpha, the variant discovered in the UK. Alpha is already around 50% more transmissible than the original strain, according to the Centers for Disease Control and Prevention.

That means the variant can more easily spread among kids, too. Indeed, several countries have recently recorded a higher share of coronavirus cases among children.

In Israel, half of the 125 new infections reported on Monday were among children, according to the country's health ministry. Around 70% of Monday's new infections, the ministry added, were caused by Delta.

Researchers in Scotland also found that Delta cases were present mostly in younger age groups. In the UK overall, a study still awaiting peer review found that coronavirus infections are now five times more prevalent among children ages 5 to 12 and young adults 18 to 24 than among those older than 65. (Delta now accounts for up to 99% of the UK's coronavirus cases, according to Public Health England.) Most young adults who recently got infected were unvaccinated, according to that study.

In the US, meanwhile, kids represented nearly 25% of new weekly cases for the week ending June 17, despite making up around 22% of the population. That's higher than the overall share since the start of the pandemic: 14%.

The US's Delta cases appear to have tripled in just 11 days, from just 10% of all coronavirus cases sequenced in early June to 31% of all cases last week, according to an estimate from the Financial Times. At that rate, experts predict Delta will become the nation's dominant strain in a matter of weeks.

"With these new, more contagious variants, I think we're going to see that children and schools do become more of a focal point of spread," Scott Gottlieb, former commissioner of the Food and Drug Administration, told CNBC on Monday.

Kids could spread the virus to unvaccinated adults

Seven-year-old Jacquie Carney runs to hug her grandma, Donna Vidrine, upon arrival in Los Angeles, California on November 23, 2020.

Disease experts say kids don't seem to be developing more severe Covid-19 as a result of Delta - or that they're are somehow more biologically susceptible to contracting the variant than adults are.

"There could be increased transmissibility of this virus, but it's increased transmissibility to all people, not just because you're a child," Ulloa said.

The Scotland researchers found that getting infected with Delta doubles the risk of hospital admission overall relative to Alpha. (Previous studies have suggested that Alpha may be 30% to 70% deadlier than the original strain.) But even if you doubled a child's risk of being hospitalized from a Delta infection, it would still be "minuscule," according to Eyal Leshem, an infectious-disease specialist at Israel's Sheba Medical Center.

That's because severe Covid-19 is extremely rare among children: In the US, kids account for just 1.4% to 3.3% of all Covid-19 hospitalizations and less than 0.23% of all Covid-19 deaths.

However, the variant's transmissibility means that kids who get infected with Delta can easily spread the variant to unvaccinated adults, or perhaps to people who see a less robust immune response to vaccines - like the elderly or immunocompromised.

Some kids may get severely ill in rare cases

Alex Glailson, a nurse technician, examines a child in Ilha de Marajo, Brazil.

Pfizer and Moderna expect to release trial data about the safety and efficacy of their vaccines in young children in the fall, then apply for FDA authorization. Until then, disease experts continue to recommend masks for unvaccinated kids.

In very rare circumstances, some kids may get severely ill from Delta. Ulloa said she has seen a few pediatric patients who were hospitalized after contracting the virus from an unvaccinated family member.

"If we've had a few cases here and there, then that's the story that we're getting: that basically a lot of the family members are vaccinated, but then they're exposed to an unvaccinated, infected person," she said.

Gottlieb told CNBC that any rise in pediatric hospitalizations could simply be due to the virus' transmissibility.

"It's just math that if more kids get infected, even if the rate of bad outcomes in kids is very low, more kids are going to have bad outcomes," he said.

Ulloa said she's also seen a few kids develop a persistent cough or fatigue similar to adult long-haulers - patients those whose symptoms last at least three weeks, but can drag on for months.

"I wonder if these different variants are more likely or less likely to cause these long-haul syndromes in kids," Ulloa said. "That's something else that we're going to be investigating."

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