Flu vaccines are just an old version of the flu strand. basically you are injecting your child with the same thing you don't want them to catch.

It's done so your child immune system can be reinforced and fight the disease from the outside. When you get vaccinated you are injected with the viruse so that your body can build up antibodies for 2 weeks. This makes it immuned to the flu viruse.

The diaphragm is what i think ur talking about

The basic building blocks of dna and rna are nucleotides