Why the Delta Variant Is Giving More Children Covid

(Bloomberg) -- Covid-19 cases among children are surging across the world amid delta-fueled outbreaks, spurring hospitalizations and raising concern about the risk of severe illness and persistent “long hauler” symptoms. It’s also prompted questions about the safety of schools.

1. How common is Covid in children?

In the U.S., as of Sept. 16, more than 5.5 million children and adolescents had tested positive for the coronavirus since the start of the pandemic, according to the American Academy of Pediatrics. That represents 15.7% of all cases, though individuals under 18 make up 22.2% of the U.S. population. However, after declining in early summer, pediatric cases have increased exponentially and comprise a higher share of the total -- 25.7% in the week ending Sept. 16, or almost 226,000 cases. That surge, coinciding with increased circulation of the delta variant, has translated into more Covid-related hospitalizations among children and adolescents, although serious cases remain proportionately rare.

2. Why are children being infected more?

Delta is at least twice as infectious as the original coronavirus strain that emerged in late 2019 and is causing more Covid-19 cases in susceptible individuals across all age groups. There’s no evidence that delta is targeting children more than other age groups, but vaccination rates are higher in older people since adolescents generally got access to the shots much later. They still aren’t approved for children under 12. Vaccination of adults appears to prevent illness in children: Researchers at the CDC found emergency department visits and hospital admissions for children were higher in states with lower population vaccination coverage, and fewer in states with higher vaccination coverage.

3. How serious is a delta infection for children?

Covid-19 remains a mild disease in the vast majority of children, and there’s no evidence that delta is changing that. Severe disease after any infection with SARS-CoV-2, the coronavirus that causes Covid, in children remains rare, and hospitalization and death exceedingly rare. Among U.S. states reporting data, children made up 1.6% to 4.2% of the total number of Covid-19 patients hospitalized since the pandemic began, and 0.1%-2.0% of pediatric cases have resulted in hospitalization, according to the academy. Often children are hospitalized for other reasons and coincidentally test positive for SARS-CoV-2. Children represent less than 0.25% of all Covid fatalities in the U.S., and their mortality risk is less than 0.03%, the academy said. Some children who have had Covid may later develop a rare but serious condition known as Multisystem Inflammatory Syndrome in Children, although the cause is unknown.

4. Why are children less likely to get severely ill?

Children have a more robust innate immune response -- the body’s crude but swift reaction to pathogens -- than older adults. That typically enables kids to successfully counter the infection before it’s had a chance to spread to the lungs to cause pneumonia and the inflammatory cascade that can be life-threatening in seniors. It’s also possible that the routine pediatric immunizations that younger children receive boost their innate immune response.

5. Are children more likely to transmit delta?

The delta variant is inherently more transmissible and, therefore, will be more contagious between children, between adults, and between adults and children and vice versa. Studies and modeling of transmission patterns indicate that younger children and adolescents play a lesser role in spreading SARS-CoV-2 at a population level, and that prioritizing vaccination in older age groups yields more population-level protection against Covid. 

6. What about at school?

As students return to classes, the U.S. Centers for Disease Control and Prevention recommends prevention measures in early child care and schools, such as masking for students and staff members and maintaining adequate ventilation to reduce transmission of the virus. One study using computer modeling, released ahead of peer-review in August, indicated universal masking could reduce infections among susceptible students by 26% to 78%, and biweekly testing along with masking by another 50%.

7. Should children get vaccinated?

The case for immunizing children is much less clear-cut than it is with adults, who are at greater risk of getting seriously ill. Vaccines have received emergency authorization for use on children older than 12 in the U.S. and elsewhere, while studies are underway to assess the safety and effectiveness of shots for those younger. Pfizer Inc. and partner BioNTech SE said their vaccine was safe and produced strong antibody responses in children ages 5 to 11 in a large-scale trial. The findings could pave the way to begin vaccinating grade-school kids before the end of October, according to Anthony Fauci, director of the National Institute of Allergy and Infectious diseases. Some kids who have chronic medical conditions are at a higher risk of getting really sick from Covid, which is why some authorities have listed them as a priority group. Any recommendations will need to weigh the risk of harm from Covid against the risk of harm from the inoculation, as well as the broader benefits of vaccination, such as reducing transmission in the community and avoiding school closures. Researchers in Australia using modeling found that herd immunity is unlikely unless children ages 5 to 15 are also vaccinated.

8. Can children get long Covid?

Yes, though it’s uncertain how frequently it occurs. An analysis and review of published studies by researchers in Switzerland and Australia and found that long Covid might be less of a concern in children and adolescents than in adults, with symptoms typically persisting for less than 12 weeks. Still, the authors found that studies of the likelihood of persistent symptoms in children are limited and difficult to interpret. In some cases, children who had an infection weren’t compared with uninfected “controls” to identify whether chronic fatigue, anxiety and other ailments could be indirect consequences of the pandemic, such as lockdowns and school closures. In one large, self-selected, online study, only 13.5% of eligible participants responded, leading to a potential response bias, for example, toward those experiencing lingering symptoms being more motivated to participate, resulting in an over-representation of symptom prevalence. 

The Reference Shelf

• CDC guidance on schools and child care programs and its data tracker.
• A comprehensive research brief from Murdoch Children’s Research Institute.
• Bloomberg’s global vaccine tracker.
• More QuickTakes on variants, the case for boosters, vaccine mandates and mRNA.
• Bloomberg Opinion’s Sam Fazeli looks at the U.K.’s single-shot approach for children.

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