They are still studying this. That's why both the CDC and the Mayo Clinic say basically we still don't know yet. Which is what your study says.
I put up 2 links, both from mid April.
Your Feb 18th link says that we don;t know yet. Which is all my 2 links said. I am actually kind of surprised you didn't notice that.
It directly says that. Here's from your article.
Quote
What have they found?
Results so far are preliminary. In a study in the U.K. of the AstraZeneca vaccine, volunteers are checked for SARS-CoV-2 infections using weekly self-administered nose and throat swabs. According to results as of Dec. 7, after a single dose, the group that received the vaccine had 64% fewer positive swabs than the placebo group, suggesting the vaccine cuts down on infections as well as disease.
. When will we know more?
.
As vaccination becomes more widespread, researchers should be able to discern the effect on infection and transmission patterns, although it can be difficult to distinguish the impact of inoculations from that of measures such as lockdowns and mask mandates. The completion of the vaccine trials testing for asymptomatic infections will bring additional information. Two trials are expected to finish in April.