New weekly allocations of doses are posted every Tuesday. Beginning the following Thursday,states can begin ordering doses from that week’s new allocation of 1st doses. Beginning two weeks (Pfizer) or three weeks (Moderna) from the following Sunday, states can begin ordering doses from that weeks new allocation of 2nd doses. After doses are ordered by states, and shipments begin the following Monday. The entire order may not arrive in one shipment or on one day,but over the course of the week.
Second doses are opened up for orders on Sundays, at the appropriate interval two or three weeks later according to the manufacturer’s label, and with shipments occurring after jurisdictions space orders. Shipments of an FDA-authorized secure and effective COVID-19 vaccine continue to reach at sites across America. Vaccinations began on December 14,2020. https://www.hhs.gov/coronavirus/covid-19-vaccines/index.html
Pfizer Vaccine Data - https://data.cdc.gov/Vaccinations/COVID-19-Vaccine-Initial-Allocations-Pfizer/saz5-9hgg
Source: cdc.gov