The movie is the third, albeit loose, screen adaptation of Richard Matheson's novel from 1954 bearing the same name. A decent synopsis can be read here.
From Good Intentions to Misadventure
A scientist publicly announces that she represents some unknown group of scientists who allegedly managed to develop a be-all-end-all cure for cancer. Unfortunately it quickly becomes apparent that the "cure" actually is a wolf in sheeps' clothes and the first batch of people treated with it precipitate an infectious epidemic of extreme and unprecedentedly fatal proportions. Consequently, most of the population of the earth is decimated; a small portion of humanity survives but not escaping a horrible transformation into extremely aggressive animal-like humanoids. Only a very few humans prove to be naturally immune and survive the onslaught unscathed and unmutated.
Although it ultimately wreaked havoc in the most extreme way, the motives for developing the "cure" were considered to be most noble and worthy (curing cancer). Thus the reader is nudged into thinking that, in case a real plague should take place, its underlying cause must have been, at least, morally acceptable and that in all likelihood 'something must have gotten terribly wrong along the way.' It must be a tragic misfortune by misadventure, no conspiracy theories needed, you see. Our leaders would never do such an evil thing intentionally. Yadaa, Yadaa...
This subtle brainwashing tactic helps provide a cover for possible perpetrators orchestrating any future plagues to hide behind; plagues that, in contradistinction to the one referred to in the movie, in reality are not accidentally and unintentionally brought about by misadventure but rather are administered by malevolent and premeditated willful acts. Indeed, what a wonderful world we're living in...
Martial Law Scenery
According to well-established contemporary cinematographic tradition (or perhaps 'doctrine' would be a better word), the military is seen to have totally assumed (read: usurped) the role of the police as a means of crowd control and law enforcement during times of crises; the Posse Comitatus Act has again been swept under the rug completely. Examples of other modern movies featuring a similar police state theme are The Day the Earth Stood Still (2008) and Transformers (2007).
In addition to the military gone crowd control, civilians are subjected to mandatory eye scanning tests; the purpose of which is to help identify infected people. The general effect on the viewer is to make the public get used to not only being identified immediately and on immediate demand from military law enforcers but it is also to help the public get used to being herded like cattle at the discretion and say-so of your local military overlord. It thus follows naturally that this kind of scenery portrays yet one more martial law type of setting in which human rights have been wiped off of the map on the contingency event of a national/international disaster coming into actuality.
Vaccine As Remedy
A degenerate female humanoid has been captured and now serves as 'human' guinea-pig to Dr. Robert Neville - the protagonist of the movie. With the ultimate aim of discovering an effective vaccine to cure the infected, he administers an experimental vaccine to his newfound guinea pig.
If successful the viewer is invited to put stock into the notion that vaccines are your weapon of choice to wage war against, and to ultimately defeat, any infectious viral/bacterial diseases that is wreaking havoc.
Of course, never in the movie is the 'vaccine as remedy' assumption questioned.
Typical Human Behavior is now entirely absent
Dr. Neville, who by the fact that he is a medical doctor as well as solitary automatically radiates a natural sense of authority in his role as judge and observer, decides that the infected have been totally dehumanized and it is therefore entirely justified to, if need be, deal with them in a ruthless manner (no normal moral restraints apply which are courtesy of a healthy and humanely functioning conscience).
Bob Marley's Musical Vaccine for a Spiritually Ailing Humanity
Although the analogy with the words of Bob Marley (who I, by the way, regard as a great artist as well as human being and I commend him for making the above suggestion) at first glance is meritorious, by association with the wise words of Marley, it also imbues into the viewer a good dose of unwarranted faith into the idea that vaccines are unconditionally peachy and beneficial to humanity.
The infected won't stand to reason
The unrelenting hostility and absolute lack of willingness of the infected to stand to reason urges the protagonist to seek a desperate solution in dealing with a desperately threatening situation. The underlying theme iterated once again is that it is allowed for uninfected to ruthlessly deal with those who are infected as they have been utterly dehumanized. It's a recurring mantra that is seen in basically all akin viral horror movies (of the last few years). See for instance my analysis of "28 Weeks Later (2007)" or "The Invasion (2007)."
And so it is announced that the effective remedy for the genocidal infectious epidemic is stored inside the blood contained in a test-tube, from which effective remedial vaccines are to be derived and administered to the infected.
However, since one would be dealing with most reluctant recipients, the movie shows, the vaccines would have to be administered in a brutish and dictatorial manner. This implied theme of involuntary vaccine administration of course fits very well into the police state mentality already given plenty of airtime earlier in the movie.
The Cure is a Vaccine
The movie closes with the handing over of the vial containing a blood sample of a cured infected. Thus it is suggested that the automatic answer to any future infectious disease epidemic lies with the concept of the vaccine. Therefore, if an infectious disease comes hither home hitting hard, people may be reminded of this movie's last scene and helped into accepting remedial/preventative vaccinations, no questions asked.
Nowhere in this propaganda piece, is it addressed even once that vaccines have long been suspected of being harbingers of death and disease rather than bringers of life and remedy. Indeed, it can be argued, for instance, that the whole AIDS epidemic is iatrogenic rather than zoonotic in origin, meaning that its cause is more likely man-made than some kind of rare and spontaneous inter-species pathogenic cross-over. In addition to the article referred to in-place, see reference 1. Quite similarly can it be argued that the recent appalling upsurge in cases of autism is also induced by eugenically inspired power mongers, see reference 2.
Note: the longer quotes used here, were drawn from this source.