Seems clear from my perspective. Two doses are recommend by manufacturers. Anything more or less is pure speculation at best. Why speculate in absence of a way to test your hypothesis?
> Anything more or less is pure speculation at best
There are two lines of evidence. The first is empirical. It It appears that one dose of Moderna _is_ highly effective, perhaps 85% or more. Note the treatment-control divergence after about fourteen days [1]. The second is theoretical. From our ample medical experience with other vaccines, there is strong prior reason to think that one dose is likely to work well, and that a second shot in the distant future would be even better than a second shot after three or four weeks. Booster shots are given a.) as backup for people who don't seroconvert after one dose b.) to trigger a secondary immune response. In light of a.), we shouldn't be surprised by the 85% number (most people seroconvert; there's no partial immunity, you either seroconvert or you don't). In light of b.), we should be very skeptical of the four week interval, especially since the secondary response takes about two weeks to develop. It's shorter than the interval for every other vaccine.
Agreed. It's also important to remember that the 3/4 week dates for the second dose were not chosen based on it being the most effective timeline, but because it was the minimum time needed to complete the studies as quickly as possible. If they'd chosen 8 weeks we wouldn't have US approval yet. If they'd chosen 12 weeks we wouldn't even know if they were effective yet.
The main unknowns aren't around short-term efficacy, but long term immunity. If it turns out that a single dose provides ~80% protection but only for 3 months, whereas the second dose provides strong long-term protection, the one-dose scenario would be significantly worse.
Vulnerability isn't binary. You're not immune one day and susceptible the next. It's much more likely that immunity to getting sick might start decreasing over time, but still remain relatively high. So, perhaps 80% in 3 months, 60% in 6 months, and 30% in 9 months to use made up numbers. Additionally, production is still ramping up so it's highly unlikely that we'll have less vaccine in 3 months than currently. We'll also likely have 1-3 more approved vaccines by then as well.
Unfortunately, we don't know the exact numbers so following this strategy (which I agree might make sense) is somewhat of a gamble. Maybe the numbers are not very favourable therefore the choice shouldn't be portrayed as such a simple one as in the comment I replied to.
Because the manufacturer recommendations are based on achieving the best outcome for the individual receiving the treatment. But we're in a global pandemic, a situation the world has not faced in living memory. A different quality metric might be appropriate under these circumstances.
So even though the manufacturers (the companies that developed the vaccines, the scientists, the people running the trials, the ones that know the data and went through a full year of tests) keep on recommending 2 doses and the advice given to the UK government was still to stick to the 2 doses, we're now going the way that "we think we know better and it's better to try something new and untested because it's a pandemic and it might be better to have less efficiency to more people, than full efficiency to less people", even though it's, again, not tested and a shot in the dark?
Was there any testing done comparing 2 doses to one? I think it was speculation that led us to test with 2 doses because we'll, we don't have much time, 2 must be better than one.
The study we have of a two-dose COVID-19 vaccine with one dose administered showed 67% effectiveness, in line with vaccines for other diseases (including eradicated ones - polio vaccine is 80%).
There are two lines of evidence. The first is empirical. It It appears that one dose of Moderna _is_ highly effective, perhaps 85% or more. Note the treatment-control divergence after about fourteen days [1]. The second is theoretical. From our ample medical experience with other vaccines, there is strong prior reason to think that one dose is likely to work well, and that a second shot in the distant future would be even better than a second shot after three or four weeks. Booster shots are given a.) as backup for people who don't seroconvert after one dose b.) to trigger a secondary immune response. In light of a.), we shouldn't be surprised by the 85% number (most people seroconvert; there's no partial immunity, you either seroconvert or you don't). In light of b.), we should be very skeptical of the four week interval, especially since the secondary response takes about two weeks to develop. It's shorter than the interval for every other vaccine.
[1] https://arstechnica.com/science/2020/12/fda-releases-data-on... [2] https://www.cdc.gov/vaccines/schedules/hcp/imz/child-adolesc...