Expert has to explain vaccines to Trump again -- even after pharma companies spent hours explaining it yesterday

President Donald Trump might still be having a hard time understanding how vaccines work.

CNN's Jim Acosta tweeted that at the start of an event at the National Institute of Health, infectious diseases expert Dr. Tony Fauci was forced to, again, explain to Trump how long it takes to develop vaccines. He cited past examples using other viruses and the timeline for developing those vaccines.

Monday, Trump met with about a dozen pharmaceutical executives and demanded they rush a vaccine for the coronavirus.

"At meeting with pharma companies, ⁦Trump says he is hearing that a vaccine can be ready in three to four months," reported Reuters reporter Jeff Mason.

Dr. Tony Fauci cut in to make it clear to reporters that any vaccine will not be ready to send to people for at least a year.

Vaccines take time to create, but they also require testing on animals. From there, they’re often retooled and tested again on animals. It can go through several versions before scientists feel it is safe enough to test on humans, much less be ready for mass distribution.

“During the meeting, several of the experts and the pharmaceutical industry CEOs had to explain to the president time and again that they cannot necessarily rush a vaccine on to the market,” said Acosta in a CNN report Monday. “The president was sort of asking as he was going around the room, well, how quickly can we get a vaccine out on the market, and do it in three or four months.”