My son had n1h1 at xmas 2010 can you catch it again and can weaken the lung further as he already has chronic lung desease?

Should be immune. Immunity to a given strain of the flu should be long term if your kid has a regular immune system.Since flu has many strains, a flu shot every year is needed to help avoid new strains. The actual h1n1 strain was part of the last 2 flu vaccines but may not be later.Unless you had your kids strain confirmed by a specialty lab it may not have been h1n1, simple offfice tests are not that specific.
Flu shot immunity. H1n1 given before is now incorporated with flu shot this year .Child should get flu shot every year especially if he has chronic lung disease.