Shares of Inovio Pharmaceuticals Inc. /zigman2/quotes/202993817/composite INO +2.97% were halted and then fell 33.6% when they resumed premarket trading on Monday when the company said the Phase 2/3 clinical trial for its COVID-19 vaccine candidate was in a "partial clinical hold" while it answered additional questions from the Food and Drug Administration. The hold is not due to an adverse event, which is what paused the Phase 3 study for AstraZeneca /zigman2/quotes/200304487/composite AZN -0.03% /zigman2/quotes/203048482/delayed UK:AZN -0.60% and the University of Oxford's experimental coronavirus vaccine. Inovio said in a news release that it is working on answering the regulator's questions, it plans to respond to the FDA in October, and then the agency has 30 days to issue its decision about whether the trial can move forward. The Phase 1 trial is still underway. Inovio's stock has soared 413.3% so far this year, while the S&P 500 /zigman2/quotes/210599714/realtime SPX +0.47% is up 21.%.