The omicron variant could spread two to three times faster than delta, according to a new report from the Imperial College London COVID-19 response team.

The study, which has not yet been peer-reviewed, also estimated that the risk of being reinfected with omicron is more than five times higher than that of delta.

Data could change as more information on omicron's spread is gathered, though the study offers an early indication of how much more transmissible the new variant is compared to delta.

-ABC News' Cheyenne Haslett, Dr. John Brownstein and Sony Salzman

Due to a "substantial increase in cases across the league," the NFL announced that several weekend games have been pushed back.

Saturday's game between the Las Vegas Raiders and Cleveland Browns has been moved from Saturday to Monday.

The Washington Football Team vs. Philadelphia Eagles matchup and Seattle Seahawks-Los Angeles Rams game have both been moved from Sunday to Tuesday.

New York state reported 21,027 cases Thursday, setting a new single-day high, Gov. Kathy Hochul's office said.

"The winter surge in COVID-19 cases is a reminder that the pandemic is not over yet and we must take extra care to keep ourselves and each other safe," Hochul said in a statement. "The vaccine is still our best weapon to defeat the virus."

-ABC News' Josh Hoyos

Southwest CEO Gary Kelly has tested positive for COVID-19 after testifying at a Senate hearing Wednesday alongside other airline executives, a Southwest spokesperson said.

He was not masked during the hearing.

Kelly, who is fully vaccinated and boosted, has mild symptoms, the spokesperson said.

ABC News reached out to the airlines whose executives were next to Kelly at the hearing.

United Airlines CEO Scott Kirby and Delta operations chief John Laughter tested negative Friday.

American Airlines CEO Doug Parker plans to test Friday afternoon, according to the airline. Sara Nelson, international president of the Association of Flight Attendants-CWA, said she will test Friday and in the coming days.

Senate Commerce Committee Chair Maria Cantwell told ABC News that committee members will "follow the protocols" for testing.

-ABC News' Mina Kaji, Allison Pecorin and Sam Sweeney

The potential timeline for when children under 5 may have an authorized vaccine is now being pushed back.

Data for a two-shot vaccine was initially expected by the end of the year, but now Pfizer/BioNTech say they hope to have data with a third shot in the first half of 2022.

Pfizer/BioNTech said they "will amend the clinical study evaluating the safety, tolerability, and immunogenicity of the Pfizer-BioNTech COVID-19 Vaccine in children 6 months to under 5 years of age. The study will now include evaluating a third dose of 3 µg at least two months after the second dose of the two-dose series to provide high levels of protection in this young age group."

An early look into the study data suggested that the two doses at a smaller volume was not as effective for kids ages 2 to 5 as it was for the 16 to 25 population, so scientists are going to add a third dose and see if the vaccine is as effective. There were no safety issues reported in the early data analysis.

Pfizer/BioNTech added in a statement, “The decision to evaluate a third dose of 3 µg for children 6 months to under 5 years of age reflects the companies’ commitment to carefully select the right dose to maximize the risk-benefit profile. If the three-dose study is successful, Pfizer and BioNTech expect to submit data to regulators to support an Emergency Use Authorization (EUA) for children 6 months to under 5 years of age in the first half of 2022.”

-ABC News' Eric M. Strauss