If the trial start wasn't priced in, PPS would have held or kept trending up. Is it "priced out" now that it dumped back down? No. This is just news driven trading, one of the most common activities in the market.
Trial start was priced in; this was just a trading event.. the rumor was bought, and the announcement of the injection, the News, was sold.
The market at large was not caught unawares that there were trials in Brazil and suddenly updated their valuations.. the market at large is still unaware, I'd argue; this was a non-event to most investors, and in most cases they'd be right.
What isn't fully priced in is the results.. because they're unknown and we've already had a few covid trials with what could be construed as unclear results.
Just because the PPS isn't where you, as an individual, want it to be, doesn't mean the stock is over or undervalued.