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That the US might adopt a 1 dose regimen or significantly delayed 2nd dose for vaccines already authorized seems more fanciful thought experiment than tractable policy. Pretty much all institutions and incentives are lined up against such a change and not without reason.
Current vaccines are authorized via EUAs from FDA, which both clearly state terms of use including a two-dose regimen. Moderna’s EUA says the vaccine is “administered as a series of two doses 1 month apart…”
“…Individuals who have received one dose of Moderna COVID-19 Vaccine should receive a second dose of Moderna COVID-19 Vaccine to complete the vaccination series.”
https://www.modernatx.com/covid19vaccine-eua/eua-fact-sheet-providers.pdf
https://www.modernatx.com/covid19vaccine-eua/eua-fact-sheet-providers.pdf
Providers can’t just willy-nilly decide to use these vaccines another way. To do so requires changing the EUAs, which means experts at FDA & VRBPAC would have to re-review evidence to assess efficacy and safety of a different regimen.
Trials already completed for these vaccines weren’t designed to assess other regimens. Therefore, either new trials will have to be done, or regulators would use imperfect and indirect evidence to justify changes to their recommendations.
Regulators don’t seem to relish the idea of overturning the apple cart. Peter Marks at FDA has already said clearly that a one-dose approach is “foolhardy”
https://www.c-span.org/video/?507261-1/fda-holds-news-conference-authorization-pfizer-vaccine
https://www.c-span.org/video/?507261-1/fda-holds-news-conference-authorization-pfizer-vaccine
He goes on to say: “from the FDA perspective we would be recommending that people complete the two-dose series so we actually that they are truly protected at the rate of approximately 95%.”
VRBPAC member Paul Offit is also skeptical. About the UK’s proposed 3-month gap between doses of the Oxford/AZ vaccine he said: “We don't have the data on the efficacy of one dose… That's why you do the studies.” https://www.businessinsider.com/expert-reaction-uk-untested-vaccination-strategy-single-dose-pfizer-2020-12
Moncef Slaoui of Operation Warp Speed is also not a fan of changing up a regimen post-hoc. “It’s important, I think, to use the vaccine based on how you studied it” he said about the UK delayed dose approach https://www.politico.com/news/2020/12/30/astrazeneca-vaccine-april-452371
CDC/ACIP would also weigh in. Currently CDC guidance says: “Limited data are currently available regarding the efficacy of a single dose. Patients should be counseled on the importance of completing the two-dose series to optimize protection.”
https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html
https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html
Officials aren’t being obstinate, they are weighing costs and benefits based on the evidence at hand and will tend to err on the side of evidence rather than conjecture. Even getting to the current EUAs and guidance was an arduous process with a lot of tire-kicking.
Also unclear to me how executives and experts at Pfizer and Moderna would feel about their products being in ways that are different from how they had been studied. My guess is that most would not be comfortable with such a change.
Pfizer came out with a statement saying that there are "no data" to demonstrate that a single dose of its coronavirus vaccine will provide protection from infection after 21 days https://www.axios.com/pfizer-single-dose-data-716702dd-324f-42b9-b88d-07df43ca198a.html
Even if new guidance were handed down from federal officials, it would still be up to states to put it into practice. We can guess that even if some states might be amendable to such changes, many might not.
Then there’s the fact that many providers might refuse to give a single dose or a significantly delayed 2nd dose. We’re already seeing significant backlash to the UK’s delayed dose proposal from providers there https://www.politico.eu/article/uk-doctors-rally-against-new-coronavirus-vaccination-strategy/
Those prioritized for vaccination early are those most at risk, such as the elderly. Postponing second shots for these individuals could place them “at the highest risk of death if they contract COVID-19” during the delay.
It will also cause logistical problems for vaccination sites. In the US, states have built current Covid vaccine delivery around the recommended two-dose regimen. It’s not a simple thing to change this up on the fly.
So, even if all the regulatory and programmatic hurdles were overcome, we’d add yet another layer of patchwork to US vaccine coverage because only some states and some providers would be implementing the new approach.
Finally, worth noting that we could have a one-dose vaccine becoming available through an EUA in the next month or two: the J&J vaccine. The US has already pre-purchased 100m doses. Fingers crossed that it's safe and effective. https://www.nytimes.com/interactive/2020/health/johnson-johnson-covid-19-vaccine.html
Many are rightly disillusioned with the pace of vaccine roll-out, but the most constructive use of energy may be toward the unglamorous task of improving delivery and administration of the vaccines we have through our existing (albeit imperfect) systems.
