US FDA vaccine strength Phase III clinical trials appear to have a minimum of 30,000 participants in the typical 50/50 experiment/control distribution, whereas

US FDA vaccine strength Phase III clinical trials appear to have a minimum of 30,000 participants in the typical 50/50 experiment/control distribution, whereas e.g. Novavax's U.K. based Phase III trial was half that. AZ's US Phase III trial was delayed at least a month because of a possible correlated adverse event and per "reliable rumor" a lack of candor from AZ (in general both AZ and Oxford have done about the worst in the West in testing and communications, not counting Sputnik V). They now have their US efficacy data but have not yet made an application for an Emergency Use Authorization from the FDA no doubt due to not yet having safety data from half their subjects who got the vaccine, which was the gate for the mRNA vaccine applications. None of the other vaccines have had EUA applications, although we should see one from Novavax pretty soon. J&J or rather Janssen's production capabilities are mostly in the EU, we in the US have been getting doses made in the Netherlands with fill and finish (bottling) in the US. Unfortunately Emergency BioSolutions, a company who's competence is all political, not production, got the initial subcontract to make Janssen doses in the US, and predictably has done a horrible job. To make a long story short their Baltimore factory has not received FDA approval and just plain shouldn't without a complete top to bottom housecleaning, everything from firing every person in it to actually keeping the equipment and rooms etc. clean and free of mold and bacteria (yes, it's that bad). Merck though has recently agreed to make doses. So we've run out of "banked" pre-authorization supplies of Janssen doses, and are not getting a whole lot from the Netherlands. Moderna and Pfizer appear to be in much better shape because they're not depending on delicate cell cultures to make their vaccines, production is much simpler except for the microfluidics that mix the lipids and mRNA. Biologically the most complicated thing is making DNA using E. Coli, that's much easier to do correctly than cell cultures, especially in bulk. As for total doses administered in the US, see https://covid.cdc.gov/covid-data-tracker/#vaccinations https://covid.cdc.gov/covid-data-tracker/#vaccinations As of yesterday only 6.9 million of Janssen out of 190 million total. And you're right about the efficacy, Janssen's objective from the beginning was to develop the single most effective one dose vaccine, which they've achieved, although they're trying two doses eight weeks apart in a separate US based Phase III trial.