Hi, I did extensive research and sought medical advice prior to getting my daughter the CP vaccine. Here's what I know.
No vaccine guarantees life long immunity. Vaccines effects work better in some people to others. Varicella vaccine has been around for 30 years and so far, has provided 30 years immunity for (please note a 2 dose schedule has proven more effective than the original 1 shot that was given to children) in most people. Live vaccines should provide life-long immunity in most people. Even MMR's immunity duration remains unknown currently www.nhs.uk/conditions/vaccinations/pages/mmr-questions-answers.aspx
Research continues into all vaccines. If it's found we need a further dose of mmr in later life, we will know about it. Same applies to chicken pox vaccine. I personally had rubella as the vaccine wasn't available and my brother had measles despite being vaccinated.
The main reasons we do not get the CP vaccine on the NHS are:
Cost
Uptake might be lower as they would most likely combine and use the MMRV shot.
Possible increase in shingles of older generations who had CP
My doctor told me the main reason was cost.
Re shingles, there is no evidence that shingles has increased since theCP vaccine was introduced in other countries. An anti-vac website will of course say it has.
If you have the CP vaccine, that will lay dormant in you just like the "wild virus" so vaccinated people can still get shingles. However, current research shows that those vaccinated are far less likely to get shingles and if they do, it should be mild.
You cannot catch shingles. You have to have had CP or the vaccine.
You can catch chicken pox from shingles if you touch the fluid from the blisters and have never had CP or the vaccine.
If you are vaccinated against chicken pox but do go on to get chicken pox, you should just get a mild dose, eg, less than 20 spots.
There's no "herd immunity" for CP in the UK but those vaccinated against it, should get natural immunity boosters whenever they come across chicken pox knowingly or unknowingly.
Read up on Adam Finns stance on the vaccine.
Also, you can get the vaccine free in this UK trial www.uhs.nhs.uk/ClinicalResearchinSouthampton/Trials-and-facilities/Whatclinicalresearchis/FeaturedresearchExploringnewchickenpoxvaccine.aspx