evidence: As COVID-19 vaccines are being administered to anyone age 12 and up, America’s youngest children remain the last group that cannot get a vaccination. The reopening of society this summer and the development of viral mutations leaves those children exposed in new ways, even while clinical trials are underway to develop vaccines for them. [...] Here is the latest information about these and other questions. [...] For example, CDC officials announced on June 23 that there is a "likely association" between the two mRNA vaccines and myocarditis, a rare form of heart inflammation. The agency told its Advisory Committee on Immunization Practices — which makes recommendations on the use of existing vaccines — that there have been 1,226 reports of myocarditis out of about 300 million mRNA vaccinations, mostly in males ages 12 to 39. It noted that most cases were mild — with symptoms that included fatigue, chest pain, and disturbances in heart rhythm — and cleared up within several days. No fatalities were reported.