against ‘original’ Alpha covid - US avail vaccines were “... an effectiveness estimate of 97% among employees within our own healthcare system...” (first paragraph, your study, ‘introduction’)
at that same exact time, the Chinese vaccine against Alpha was about 40% effective.
subsequent variants since then mutated ways to defeat immune systems in both acquired immunes and vaccinated. It’s because of these mutations that the ‘booster’ shots and acquired immunity from prior infection from original covid provide less protection against the mutants than the original shot was against the original version of covid.
Back to China, it’s not known at this time if the original 40% effective Chinese vaccines are effective =at all= against the mutated variants sweeping thru China right now. The only clue is the funeral homes that had a few dozen deceased a day are now seeing a few hundred deceased a day according to ancedotal stories making it out of China’s wall of silence.
Except that I don’t believe ANY of the numbers put out by “official” sources - they had an agenda - By the time the vaccines were available - Alpha was already no longer prevalent (and was indeed gone in most areas of the US - )