@David L Here's the Shingrix official website describing it's mode of action:
Learn more about the mechanism of action of SHINGRIX (Zoster Vaccine Recombinant, Adjuvanted), which uses an antigen/adjuvant system.
shingrixhcp.com
What's in the vaccine is a recombinant protein for part of the virus surface antigen, along with an adjuvant that makes it easier for the human immune system to react to the protein and form immunity against it.
What recombinant means, in this setting, is that the DNA sequence of the surface protein, actually just the sequence for one part of the protein, was used to produce a that specific protein sequence in quantity in a lab. The protein is purified, then mixed with the adjuvant and packaged. The vaccine contains no live virus, no killed virus, and creates a very specific immune response. The adjuvant is a chemical cocktail that keeps the protein folded properly during storage, injection, and in the body for a while, so that the protein maintains the right shape to look like the real virus-born protein, so that the immune response is an authentic one.
For the record, I've had both Shingrix shots. The first one gave me a goose egg at injection site, for several days it was painful (but not debilitating). The second shot gave me only mild pain at injection site for a day but gave me significant fatigue and body aches the day after, though I was fine the day after that. Everyone I know who has had Shingrix has reported similar effects. I know several people who got shingles as 55+ adults and it's not something I wish to experience. Mild, brief discomfort from the shot is to me well worth it to reduce the chance of getting shingles. It's not REALLY known how often a booster for Shingrix will be needed, because it's too new. It is known that Shingrix is much more effective than Zostavax and it lasts much longer. Zostavax, though worthwhile in its time, did have a fair amount of side effects, such that moving to Shingrix as the primary vaccine, makes sense.
I hope this is helpful. There's a good video at the Shingrix site.