The sitting president of the United States, advised by the nation's top infectious diseases specialists, doesn't know what is now common knowledge; that vaccinated individuals can still spread Covid-19.

For those keeping track, this is the second major issue Biden had no knowledge of - the first being an international spat with France over a tri-lateral submarine agreement.

Speaking in Elk Grove Village, Illinois on Thursday, Biden urged more employers to institute strict vaccine requirements - calling them "tough medicine" that will help bring the United States out of the Covid-19 pandemic.

In addition to failing to recognize naturally-acquired immunity for individuals who have recovered from Covid, Biden made clear that he has no idea vaccinated people can still spread the virus.