Is that Michael McIntyre on his latest comedy roadshow?

Honestly, it isn't...

It's a recording of Abbot & Costello

Jesus, you still don't get it.

It is a vaccine, and protects against the known strains that they have developed it against.

Yes it mutates, but if we didn't have the vaccines, then infection rates of all types of flu would be far higher than they are now.

People need to stop believing that the flu vaccine is a panacea for all flu viruses. It isn't.

But it is still a vaccine against those strains they have identified.

Mutations to the measles virus in and of themselves have shown to render it ineffective.

As for your polio analogy, research the polio outbreak in the Congo in 2010.

Over 400 verified cases with an almost 50% mortality rate, even amongst those who were vaccinated. This was a vaccine resistant strain of polio.

But hey, you won't believe a word of that because you have your head so far up your own backside you believe your own faeces, and science is bad.

Autocorrupt, apologies for missing 1 spelling.

And you sir, do not understand viruses.

I do not understand them a great deal, but I do know there there are 4 genera of the family Orthomyxoviridae that are classed as Flu. Infuenzavirus A, B, C, & D.

Each genus is then subdivided into species, and again subdivided into serotypes.

This latter bit is very important.

The serotype is determined by the antibody response. It is these antibodies that a vaccine is designed to get your body to create. A vaccine for 1 serotype is ineffective against another.

Influenza A, generally find in birds, is subdivided into multiple serotypes, of which 12 are known to affect humans.

H1N1 (1918 Spanish flu, 2009 Swine flu)
H1N2 (endemic in humans, pigs, and birds)
H2N2 (1957 Asian flu)
H3N2 (1968 Hong Kong flu)
H5N1 (2004 Bird flu)
H6N1
H7N2
H7N3
H7N7
H7N9
H9N2
H10N7

Influenza B is less common, almost exclusively infects humans, and has a slower mutation rate than A. Currently only 1 known serotype. But it does mutate meaning lasting immunity is not possible.

Influenza C is less common again, but affects humans, dogs, and pigs.

Influenza D not yet seen in humans.

The problem is that of mutation. Whilst a vaccine may target a specific serotype, once it's mutated, it's useless and a new vaccine had to be made.