mask machine video，mask machine video，mask machine video，mask machine video，Almost 72,000 children and teens caught Covid-19 last week -- a "substantial" increase from a week earlier, the American Academy of Pediatrics reported Tuesday.The group counted 71,726 new cases from July 22 - 29. That is a "substantial" increase from the nearly 39,000 cases reported a week before, and five times as many kids who were sick at the end of June. The definition of a child varies by state but generally includes those up to age 17 or 18.After decreases in reported cases over the past couple of months, the July numbers started trending upward again as the highly transmissible Delta variant of the virus became dominant in the country."That's high and considering the fact that we are vaccinated now, what that's telling us is that unvaccinated people are getting infected in higher numbers because the virus is more infectious with the Delta variant," said Dr. Yvonne Maldonado, chief of the division of infectious diseases in the Department of Pediatrics at Stanford Medicine and chair of the AAP committee on infectious diseases.More than 4.2 million kids have tested positive for Covid-19 since the start of the pandemic. Children and teens represented 19% of reported cases in the latest weekly data.The report comes as schools have just started or will soon start, with some requiring no masks or social distancing, and as cases in many parts of the country are surging and hospitalizations at levels not seen in months.