[Karsten (OP)]

So they say that one flu shot offers about 60% protection. Does that mean that a second flu shot would increase the immunity? If yes, does it offer protection for 60% of the remaining 40% of the first vaccination and increase the total protection level to 84%?

[evan_au]

The Influenza virus ("flu", for short) undergoes frequent mutations and reassortment, meaning that a large fraction of the population may have no immunity to a new flu strain ( http://en.wikipedia.org/wiki/Influenza_A_virus#Evolution ).

Designing a flu vaccine involves making a "guess" about which strains of flu are most likely to be circulating in the population in about 6 months time, the normal lead time for mass production of flu vaccine (but efforts are underway to enter production more quickly http://en.wikipedia.org/wiki/Flu_research#Current_major_flu_research_contracts ).

The 60% protection means that most years they guess the upcoming strains correctly, that the flu virus does not mutate too quickly, and that it produces a good immune response in most of the recipients. A second seasonal flu injection may increase the strength of the immune response in an individual, but it won't protect against novel strains of the virus.

To get a much higher level of protection (like 84%), you would want to receive a vaccine designed at the end of the flu season - not exactly feasible!

An alternative approach is a medication which interferes with the functioning of flu genes, but there are signs that some strains of the flu virus may be developing immunity to such medicines (eg see http://en.wikipedia.org/wiki/Flu_research#Anti-viral_drugs ).

[CliffordK]

So, if you get a 2012 flu shot, it will consist of 3 strains of flu, and will give you essentially 99% protection against those 3 strains, but not other strains.
Repeated dosing with the 2012 flu shot, will still only protect you for those 3 strains.

If you are dosed with the 2011 flu shot and the 2012 flu shot, then you will be vaccinated for 6 different strains of the flu. 

Is there any research to indicate whether a person that annually gets a flu shot gets any better immunity than someone that gets the flu shot for the first time?

[Karsten (OP)]

Thank you for those answers. Always interesting how much more sense it makes to ask someone who might really know rather than just listen to the news.

The folks that throw around  the 60% number are not clear about that you most probably will not get the flu you have been vaccinated against, but that there is a 40% chance you might get infected by another strain. This is particularly confusing when they say that the flu shot was a good match this year.

I also heard that the protection rate is usually 60%. Why is it never much higher? Why would they not be able to match the mix of strains much better or worse some year?

[Lab Rat]

With a weakened strain vaccination, people often slightly feel the effects of the flu while their body fights off the weakened virus.  By that same logic, I think that if you received multiple weakened vaccines, you could feel the effects longer, or they would be slightly worse. 

[wolfekeeper]

I also heard that the protection rate is usually 60%. Why is it never much higher? Why would they not be able to match the mix of strains much better or worse some year?

As evan has basically said in a longer form, it's because of the delays in production relative to the mutation rate of the flu virus- 40% of the flu has evolved far enough away from the vaccine so that it no longer works.

If they could mass produce flu vaccine very quickly then they could potentially greatly improve this.

[confusious says]

Basically what you are saying is true, though the protection is only for 'known' popular influenza viruses at that point in time, because remember that viruses are mutating and changing all the time.

[lukesopie]

Well, I'm new over here but I'm having Vitamin-C with Zinc tablets : Sugar Free Chewable - Antioxidant for Immunity. But  I'm confused about do I need to have anything with it?

[Colin2B]

...I'm confused about do I need to have anything with it?

Well, I’m confused as to why you are trying to spam us with your cheapo, poor quality product.
Bye

[Spam3-160920]

While many people globally have built up immunity to seasonal flu strains, COVID-19 is a new virus to which no one has immunity. That means more people are susceptible to infection, and some will suffer severe diseas

[evan_au]

seasonal flu strains... COVID-19 is a new virus

There is a well-established process for making a flu vaccines against the strains expected to be most common next year. This process is well-established, and works with a 6-9 month lead time to produce a new vaccine in bulk.
- The methodology is well proven, and the vaccine has a known risk profile, so it doesn't need big trials before being distributed.

Because COVID-19 is a new virus, there is no established process to produce a vaccine against it, and the vaccine will have an unknown risk profile, so it needs extensive Phase 2 and Phase 3 trials.
- That means the date of release for a COVID-19 vaccine is quite uncertain - a vaccine may even be rejected as "too risky for use on healthy people" as a result of the Phase 3 trials.