At the start of the pandemic, coronavirus transmission among children appeared to be low. But the virus now appears to be quickly spreading among children participating in youth sports and other activities, researchers say—and those infections could be fueling outbreaks across the country.

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Data shows after-school activities are driving coronavirus outbreaks

CDC Director Rochelle Walensky during a White House briefing last week said after-school activities are creating clusters where coronavirus can spread among children—which, according to new data, can fuel larger coronavirus outbreaks that put adults at risk. Specifically, public health officials and epidemiologists have suggested school sports, which may involve close indoor contact, are now a major source of the coronavirus's transmission among communities, the Wall Street Journal reports.

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and chief medical advisor for the White House's Covid-19 response, during an interview with ABC's "Good Morning America" last week, warned about the coronavirus's spread among children participating in youth sports. "We're finding out that it's the team sports where kids are getting together, obviously many without masks, that are driving [the virus's transmission], rather than in the classroom," Fauci said.

For example, CDC researchers, in a report published in January, linked two high school wrestling tournaments in Florida in December 2020 to 79 coronavirus infections and one death.

Similarly, data from Michigan shows hundreds of the state's coronavirus cases and clusters have been linked to K-12 sports, including:

• 376 coronavirus cases and 100 clusters tied to basketball
• 256 cases and 52 clusters tied to hockey
• 190 cases and 55 clusters tied to wrestling

Overall, coronavirus cases among Michigan residents ages 10 to 19 have increased by 133% during the past month, a growth rate faster than seen among any other age group in the state, the Washington Post reports. The state's epidemiologists said the infections appear to have spread through activities "including sports, but not limited to sports," rather than in the classroom.

Kris Ehresmann, Minnesota Department of Health's director of the division of infectious diseases, said her team of researchers have found youth clusters have spurred the virus's community spread "to a degree not seen in previous spikes."

Michael Osterholm, director of the University of Minnesota's Center for Infectious Disease Research and Policy, said, "Until now we haven't seen transmission like this in kids in the pandemic."

Mark Pandori, director of the Nevada State Public Health Laboratory at the University of Nevada at Reno, said a recent youth volleyball tournament is spurring "a very, very large cluster" of cases of B.1.1.7, a variant of the current coronavirus.

In Minnesota, health officials have confirmed the B.1.1.7 variant is linked to 49 out of more than 180 confirmed or suspected coronavirus cases from a youth sport outbreak in Carver County—and they suspect the remainder of the cases also involve the variant, the Post reports. Osterholm said Minnesota's recent outbreak is similar to what health officials in Kent, a county in England, saw last year when cases among children aged 11 to 18 quickly increased.

"From my perspective, I think we haven't fully felt the effects of B.1.1.7 and many have been far too quick to dismiss the danger," Osterholm said. "I think it's going to be a challenge."

Health officials also have linked large coronavirus outbreaks to spring breaks and the Easter holiday, the Journal reports. For example, New Hampshire health officials said several coronavirus cases in the state have been linked to Easter-related events at Magdalen College of the Liberal Arts.

Philip Landrigan, an epidemiologist and director of the Program for Global Public Health and the Common Good at Boston College, said CDC's data clearly shows the coronavirus is spreading widely among young adults, noting "young adults are a mobile and active segment of the population" and they're "likely to come in contact with numbers of people of all ages." Landrigan said he "strongly encourage[s]…young adults to be considerate and kind to the people around them who are more vulnerable to the [coronavirus] than they are."

A 'lattice'-like pattern of transmission

Walensky last week said the increase in the virus's spread among children is "in part [due] to more highly transmissible variants," According to Ehresmann, these variants have influenced not just whom the virus infects, but how those infections spread.

Specifically, according to the Post, the virus in the early days of the pandemic was predominately transmitted by a comparatively small number of highly infectious individuals. Experts estimate that in that time roughly 20% of infected people spread the virus to many others and 80% infected very few people or no one at all.

However, new data indicates the virus's transmission is now more similar to the flu's transmission, with a larger number of people spreading the virus to a few other people, the Post reports. As Ehresmann explained, the B.1.1.7 variant in particular appears to have spread in Carver County cluster in a "lattice" pattern, in which each node was linked to several other cases—particularly among children and adults in the same households.

"It isn't just the sheer number of cases, but the network of interconnectivity that is striking," she said. "It is showing us how readily transmissible this virus variant can be."

States seek to control virus's spread

Officials throughout the United States are taking steps to curb the coronavirus's spread among children, adolescents, and young adults. For instance, some jurisdictions have moved coronavirus testing sites to recreation centers or other locations convenient to where students play games and practice sports, the Post reports.

In New York, Suffolk County, a suburb of New York City, became the first county in the state to require weekly testing for children participating in high school wrestling, basketball, and other high-risk sports, the Post reports. Several counties in California have done the same, and Minnesota recommends all student athletes and those involved in other in-person activities undergo weekly testing.

In Michigan, Gov. Gretchen Whitmer (D) ordered all youths ages 13 to 19 be tested before all practices and competitions beginning on April 2. The state last week also rolled out weekly coronavirus testing for 100,000 public school students who participate in spring sports, the Post reports.

Meanwhile, Florida last month declared a state of emergency and enacted an evening curfew in response to nightly parties in Miami Beach during spring break, according to the Journal.

Experts are urging people—particularly younger populations—to remain vigilant in the face of the new variants, regardless of local requirements. For instance, Leana Wen, a medical analyst for CNN, advised children to try to play outdoors when possible and urged parents to be proactive about safety protocols.

"With a more contagious variant," she said, "activities we thought were safer are now going to be higher risk" (Cha, Washington Post, 4/6; Marples, CNN, 4/8; West/Ansari, Wall Street Journal, 4/12; Associated Press, 4/13).