US government scientists are pushing back against calls for single dose regimens for two coronavirus vaccines designed to be operated with two shots, stating that there isn’t enough proof that a single dose gives long-term protection.The FDA late last year approved a two-dose regimen for vaccines from Moderna Inc. and from a partnership of Pfizer Inc. and BionTech SE. more recently it approved use of a single-dose regimen for a vaccine form Johnson and Johnson.Some scientists and lawmakers have called for shifting to a single-dose regimen for all the vaccines, citing preliminary studies displaying that one shot can be effective. They contend moving to one shot will allow the US to speed-up the pace of vaccinations.In a March 2 letter to acting Health and Human Services Secretary Norris Cochran, seven physician members of Congress urged the department “to consider issuing a revised emergency use authorization as soon as possible” that may lead to single-dose use of the Pfizer and Moderna vaccines.