The UK version is mostly a Christmas thing though you may find it at other times it is less easy. Of course the epitome of the dish is available in some chippies where you'll find hog in a duvet (something ranging from a foot longsausage in a load of bacon, sometimes battered, through to a full blown comedy 6ft long version)

The process for approval for animal vaccines and human vaccines varies quite significantly in most countries. The standards for safety, efficacy and duration of protection are lower, costs of the trials and number of trials required are lower and generally the burden is significantly less for animal vaccines. It is a large investment to have an animal vaccine approved for use in humans assuming it works in them, and even if you can use the technology to make a human effective one there remains a high risk that even though effective it will not be good enough for regulatory approval.