More American children have autism than previously thought, the U.S. Centers for Disease Control and Prevention reports.

It also finds that the COVID-19 pandemic delayed diagnosis for many, which could have lasting impact.

Data from 11 communities in the Autism and Developmental Disabilities Monitoring Network, which tracks the number and characteristics of children with autism and other developmental disabilities, revealed that at age 8, about 1 in 36 children has been identified with autism spectrum disorder (ASD).

That's 2.8% of 8-year-olds, according to an analysis published Thursday in the CDC's Morbidity and Mortality Weekly Report.

A previous estimate, done in 2018, pegged prevalence at 1 in 44 children, or 2.3%.

A second report found that progress in early detection of autism among 4-year-olds in the same 11 communities slowed during the early months of the COVID-19 pandemic.

They were less likely to be screened or identified with ASD than current 8-year-olds were at the same age.

"Disruptions due to the pandemic in the timely evaluation of children and delays in connecting children to the services and support they need could have long-lasting effects," said Dr. Karen Remley, director of CDC's National Center on Birth Defects and Developmental Disabilities.

"The data in this report can help communities better understand how the pandemic impacted early identification of autism in young children and anticipate future needs as these children get older," Remley said in an agency news release.

Who was diagnosed with ASD also changed, the report revealed.

Prevalence of autism in Asian, Black and Hispanic children was at least 30% higher in 2020 than 2018. Among white children, ASD prevalence rose 14.6% over the period.

This was the first time that the percentage of 8-year-old Asian or Pacific Islander, Hispanic or Black children identified with autism was higher than in white children. For white children it was 2.4%, compared to 3.3% for Asian and Pacific Islander children; 3.2% for Hispanic children, and 2.9% for Black children.

CDC said this was the opposite of racial and ethnic differences seen in previous reports.

Public health experts noted that the shifts may reflect improved screening, awareness and access to services among historically underserved groups.

Disparities for co-occurring intellectual disability have persisted, according to the report, which found a higher percentage of Black children with autism were identified with intellectual disability compared with those of other races and ethnic groups. This could owe in part to access to diagnostic and support services, the CDC said.

Autism was nearly four times higher in boys than in girls, but it exceeded 1% for the first time among 8-year-old girls.

Prevalence in the 11 communities ranged from 1 in 43 (2.3%) in Maryland to 1 in 22 (4.5%) in California. The CDC said these variations could be due to how communities are identifying children with autism.

The findings offer an opportunity to compare local policies and models for delivering services that could help in diagnosing and providing more comprehensive support to people with autism, the agency said.