That 78 million figure out of 128 million is consistent with the 40% to 70% worst case estimates for coronavirus infection rates. PolitiFact rates this as half true, not so much because it's half true (e.g., credible sources here, here, and many other places), but because "that is a projection, and other projections vary."
These are worst case projections that assume status quo conditions. Quoting from the PolitiFact article once again, emphasis mine,
Other estimates are similar. The Guardian reported on Feb. 11 that 60% of the global population could be infected if the virus is unchecked.
In other words, with no vaccine, no cure, no travel restrictions, no quarantines, and no social distancing, a majority of the people on the planet might be infected.