The revelation that Krumwiede falsified the Forsythia cure puts a scene where he refused to give an infected friend Forsythia into a whole new light.
Krumwiede's inclusion in the film. Whether considered New Media Are Evil or a Conflict Ball is seemingly left up to the viewer. But when you stop to consider it, Krumwiede can be considered a personification of the rumours flying around during the Swine Flu outbreak that the vaccine was an attempt to modify the recipient patients' DNA for the New World Order or whatever other shadow organisation is allegedly involved. Also works for similar individuals that claim the AIDS anti-Retroviral drugs are what kills patients, rather than the disease. As opposed to a shadowy rumour nobody can pinpoint, we get Krumwiede trying to be a Magnificent Bastard, going as far as to fake both Infection and Cure by Forsythia.
Since Sun Feng's village used the placebo, they will assume that they are vaccinated. If they return to their daily lives, they will contract the disease and everyone, including the children, will die. Moreover, Dr. Orates will have no idea where the village is since she was blindfolded and rode a car with the windows covered, so it's highly unlikely she'll be able to get there before it's too late.
When Doctor Mears gets sick in her hotel room, she immediately asks for the names of everyone who has ever cleaned her room or brought her food. Even if she gave it to just one of them (and not the other way around) it's likely that, due to the high communicability rate of the disease, and the fact that hotel staff serve multiple rooms, nearly everyone in the hotel has now been infected.
Krumwiede says that the real cure could have bad effects and cause death farther down the line. He's supposed to be grasping for some justification to explain why he would lie about the cure. However, since the researcher injected herself to make a cure without clinical trials, he could possibly be completely right.
The entire movie is a singular case of Fridge Horror. It represents a BEST CASE SCENARIO for a major emergent viral pandemic. The pandemic would play out MOSTLY how it was shown, but the actual time frame would be much, much longer. Society would suffer a complete breakdown (with the possibility of Weapon Of Mass Destruction events, loss of all utilities, a much higher level of destruction, etc.) and a vaccine, if any were to be had, would take years to test and distribute, not months. The death toll? In the hundreds of millions, possibly over a billion people. For once, Hollywood's understating the severity of the event and its aftereffects on civilization.
All of this is dependent on the details of the virus. Despite its high communicability, several medical experts have pointed out that the speed at which it kills would actually make a major epidemic much less likely. You can't say it's the "best case scenario" for a "major emergent pandemic" when both "best case" and "major" are completely arbitrary standards entirely dependent on the disease itself.
If Mitch Ernhoff has an immunity to the disease, that means that he is carrying the disease. They would never have let him out of quarantine knowing this.
That, of course, depends on how the virus works. If his system co-exists with the virus, yes, he could be a carrier. But if he lacks the right proteins for it to get a foothold, it simply won't survive in his system and he'll be able to just take a decontamination shower.