Novavax Covid-19 vaccine highly effective in late-stage trial

This is actually the vaccine technology I thought would pan out to be the best (before we learned how amazing mRNA is) and I'm not surprised that it worked out to be very effective. This is basically synthetic virus, directly injected into your arms, no intermediary viral vector, RNA, or anything. 90% effective against a highly diverse set of strains is an excellent result.

Doesn't the fact that a large percentage of people are already vaccinated with another covid-19 vaccine effect these results? I know if there is a control group you can compare the rate of infection in the two groups but it is my understanding that when they say a vaccine is 96% effective they simply mean if 1000 people are given the shot 4 percent of the people got covid during the study, right? So if many of the people who are around the trial subjects are vaccinated would this not lead to inflation of the "effectiveness" of vaccines tested later when more people are vaccinated? Or do they take into account the control group results / vaccination rates when calculating the efficiency?

EDIT: Ignoring of course the fact that the specific vaccine formulas used are likely to lose effectiveness over time as new variants pop up.

Does a full scale clinical trial and misses the window for marketability because the other companies skipped it

Well, I know many people in US that are waiting for any of the vaccines to have full trials finished just so an informed list of side effects can be listed

Is the use of adjuvants in vaccines meant for humans a normal thing, now? I had the impression that since it was not clear how the adjuvants attained their effect, adjuvants were not yet considered safe enough, although they have long been used in vaccines for livestock and pets.

Are there certain specific adjuvants now considered safe, or is it open season? What other vaccines for people are adjuvants used in now? When was the first one approved?