By Manas Mishra (Reuters) – Advisers to the U.S. Food and Drug Administration are due to meet in June to decide on whether to recommend authorizing Moderna Inc’s vaccine for children below 6 years old, and Pfizer Inc and BioNTech SE’s COVID-19 vaccine for children below 5 years old. Here is a look at some of the factors expected to be considered in this decision concerning the last age groups not yet covered by previous U.S. regulatory authorizations for COVID-19 vaccines. HOW MANY DOSES ARE NEEDED? Moderna has filed with the FDA seeking authorization for a two-dose regimen of its vaccine, cal…