SIAP as this came out yesterday, but I'm still recovering from my snow coma and haven't looked at this thread or much on COVID. But yesterday a paper came out on the Astra-Zeneca/Oxford vaccine and in the big picture it's mostly good news, especially on what their data show on the vaccine likely lowering transmission rates. The paper is linked below, as well as a timely blog entry from Derek Lowe on this in his In The Pipeline blog in ScienceMag. As usual, he does an excellent job explaining what the paper means. In addition, the 3rd link is to my post from December on the original vaccine data (and Derek Lowe blog entry on that), which has a lot of background info if interested (can't quote the post with the thread being locked, which is annoying.).
https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3777268
https://blogs.sciencemag.org/pipeline/archives/2021/02/03/oxford-astrazeneca-data-again
https://rutgers.forums.rivals.com/t...ase-ii-iii-trial-and-more.203426/post-4823821
So, the AZ adenvirus vector vaccine had a pretty shaky rollout of the clinical data from the phase III trial with missteps and many questions on efficacy, such as why did a half first dose and full 2nd dose have better efficacy than two full doses and what the best duration between doses is. The new paper which focuses on a much smaller new set of clinical data on 1293 patients with a 12-week interval between doses shows that the efficacy in this small sample was 82% overall after both doses (vs. 67% in the original trial when the two doses were 4 weeks apart) and still 76% after the first dose, which is statistically about the same. Here's how Lowe explains what seems to be some non-intuitive results (including a rationale for why the half-dose/full dose combo looked better in the original data):
Why should this be? The answer is “immunology”, and that’s not just the last refuge of scoundrels. Historically, it appears that longer delays in a two-dose regime can make things better, make them worse, or not make much difference, and the only way to be sure is to go out and get the clinical data. So even though this is not a large 12-week data set, I’m glad to see it. I think that the UK’s move to get as many first doses into the population as they can was the right one, and it’s good to see some data that at least don’t undermine it. What about the low-dose/standard dose business, though? This preprint offers a possible explanation: it turns out that the cohort that got the lower dose at first also had a longer delay before getting the second dose. So it’s possible that the apparent increase in efficacy was driven less by the lower first dose than by the longer gap between the doses.
Perhaps more importantly, as I said above, AZ also did some excellent work in this study on actually measuring for the coronavirus, via weekly nasal swabs and PCR tests, which other trials by other vaccine makers have not done. And while it's fantastic that all of the vaccines, so far, seem to be nearly completely protective against severe COVID everyone has been wondering about viral levels, shedding and transmission. This study shows that those viral levels are certainly much less, overall, which should mean greatly reduced transmission. Again here's how Lowe put it, below. This dovetails nicely with the Israeli report today on likely reduced transmissions in the real world witih the mRNA vaccine distribution in that country as per @rutgersguy1's post.
The swab data say that it has. It appears that the vaccine reduced the number of people showing PCR positivity by 50 to 70%. The actual numbers were -67% after the first dose and -54% overall, but I wouldn’t read anything into that difference, because the confidence intervals for those two measurements completely overlap. So it looks like everything is shifted: hospitalized cases end up being able to stay at home with more moderate symptoms, people who would have had moderate symptoms end up asymptomatic, and people who would have been asymptomatic end up not testing positive at all. Oh, and people who would have died stayed alive. There’s that, too.
If you just look at efficacy in preventing asymptomatic infection, you get a really low number (16% efficacy, confidence interval banging into the zero baseline). But my interpretation of that is that the overall number of asymptomatic patients didn’t change too much, because as just mentioned, the “would have been asymptomatic” group is not showing infection at all, and their numbers have been replaced by people from the “would have been showing symptoms” cohort, who are now just asymptomatic. And since transmission would seem to depend on viral load (among other factors), reducing viral load across the population (as shown by the significant decrease in PCR positivity) would certainly be expected to slow transmission. As Eric Topol noted at the time, this same effect had been noticed in the Moderna data in December. So with the numbers we have now, I feel pretty confident that yes, as one would have hoped, these vaccines also reduce transmission of the virus in the population. I believe that we should soon see this in a large real-world way in the Israeli data, where a significant part of the population has now been vaccinated.