How did they know to do that?
They already had the vaccine fully developed and were going to hold off revealing it so they could lock down people with panic, and overthrow the government that way. Remember when they were moaning (Fauci) that it normally takes 10 years to develop a vaccine and Fauci said they had no idea how long it would take. They were all moaning that there wasn't a vaccine and it could be two years or longer before they have anything to even try, and then what if it fails?.
President Trump used Operation Warp speed to dangle money in front of them so they would have to reveal there WAS a vaccine and they couldn't justify locking the country down. That lockdown was to be a one way street. We would never be free again. Around the world, a coup would take control and freedom would end - costing hundred of millions of lives for starters.
They had the 'vaccine' and didn't want to admit it, but Trump made them, and saved hundreds of millions of lives. There are still casualties from the 'vaccine' and each loss is a grievous war time casualty, but Trump saved as many as he could. Without WarpSpeed, America would fall, and with it, freedom around the world.
These links help explain: