It is true that a vaccination will not protect against every strain of flu b/c the virus does mutate continuously. The vaccines are reformulated annually based what strains of flu are likely to be most prevalent.
I don't know about "Puerto Rican Sweatshops", but Big Pharma does have a well deserved reputation for all sorts of malfeasance. Capitalism provides us with a good deal of protection from tainted vaccines; manufacturers fear getting sued, and product liability lawyers are hungrily vigilant for a chance to institute legal proceedings against anyone.
All that aside, there are numerous peer reviewed studies showing the effectiveness of flu vaccinations.