Information on the different types
of vaccines can be found here
. Approaches being considered for future vaccines can be found here
@Ren - IIUC you can't (except in that rare situation with the old oral polio vaccine - which is no longer administered) come down with the illness that an attenuated-live vaccine is designed to provide immunization for unless
the batch that was administered was defective
. And my understanding is that cases of defective vaccine batches making it into actual circulation are extremely rare occurrences.
Some vaccines, however, do lower your overall immune response such that you're more susceptible to an opportunistic
infection while your body is generating the immuno response to the pathogen in the vaccine. So I'm guessing your friend may be getting sick after being vaccinated for flu because his immune system doesn't respond well to vaccination, and either takes a bigger hit, or takes longer than usual to recover from one. If so, during that period he's more open to infection by any one of the thousands of other
flu strains in the environment that the "annual" flu vaccine (which only covers a small number of the most anticipated
strains) is engineered to help you deal with.
That's why some people who come down with a serious flu infection also wind up with a case of "shingles" or pneumonia during their illness or recovery. (Happened to me once.) Which is why they're also starting to recommend people in certain age brackets be vaccinated (or re-vaccinated) for chickenpox/shingles along with pneumonia.
However, the real benefit of vaccination is realized when most of the population is immunized because vaccines go a long way towards reducing the disease's vectors of transmission. If one person contracts in a group of immunized people, the disease doesn't spread. Possibly a few others (including those vaccinated) will become infected. But that's about as far as it will go.
If a large portion of the population is not vaccinated however, and isn't already immune from a previous brush with that infection, you have the very real potential for another Disney scenario. The deadly consequences of uncontrolled contagion are such that even in the world of military planning, germ warfare is almost automatically ruled out as an option . And it's not due to any sense of showing decency towards a real or imagined enemy. It's done mainly out of a sense of "enlightened self-interest." And the military also routinely
vaccinates troops "just in case."
When professional mayhem creators such as the military acknowledge the dangers of contagion enough to rule it out as a weapon system, and vaccinate their own as a precaution based on established knowledge of how disease propagates and spreads, I find it interesting that so many people (who pride themselves on their self-'education') - and who benefited from vaccination themselves while growing up
- are so convinced of the inefficacy and "danger" of vaccines. And with so little solid evidence to support their belief. Indeed, there's a huge amount of rock solid scientific evidence that clearly and directly contradicts the anti-vaccination argument. And now they're so convinced that their Googled "instant expertise" exceeds that of the genuine professionals in the field that they're even willing to put their own (and other's) kid's health (and lives) on the line to prove they're right. That just boggles my mind. Small wonder they had to drag that old brickbat "Conspiracy!" and toss some ad hominem
attacks into the discussion to 'support' their position.
But it is true that vaccines are not a panacea for every
individual. And they may harm a minuscule portion of the population despite all the precautions taken to assure their safety. There will always be boundary conditions and exceptions in biology. And risk will always be present with any vaccine or medication, no matter how slight.
FWIW my doctors have always advised me to avoid crowds and take it easy for a day or two after I've gotten a vaccination so my system has time to adjust. Vaccines aren't one of those simple "dose & go" or "magic bullet" solutions like antibiotics often are. They don't kill or ameliorate an infection themselves. They "encourage" your body develop its own defense against them. Which takes your body time to fully boot up.
Like most things in medicine, it seems like it's seldom "just one simple thing," but rather a combination of factors on different levels of an individual's health regime (i.e. locale, environment, genetics & gender, age, diet & nutrition, exercise, competent medical care and advice, drugs, vaccines, timing, etc.) that yields the most benefit.
I've been given to understand that vaccines (by themselves) aren't a magic cure-all. But I haven't heard immunologists or competent medical doctors claim they are either. Vaccines are, however, damn good insurance
. With vaccines it's all about risk minimization and mitigation. Because at this stage of our medical knowledge and technology, that's about as good as we can make it.