The new shots target both the original strain of the coronavirus and the omicron BA.4/BA.5 subvariants that most people are catching now. This double-barreled vaccine is called a bivalent vaccine. https://www.npr.org/sections/health-shots/2022/08/31/1120241293/fda-authorizes-first-revamp-of-covid-vaccines-to-target-omicron

For the BA.4/BA.5 boosters, the companies have submitted animal data. They have not released those data publicly, although at the June FDA meeting, Pfizer presented preliminary findings in eight mice given BA.4/BA.5 vaccines as their third dose. Compared with the mice that received the original vaccine as a booster, the animals showed an increased response to all Omicron variants tested: BA.1, BA.2, BA.2.12.1, BA.4, and BA.5.

Omicron booster shots are coming—with lots of questions — https://www.science.org/content/article/omicron-booster-shots-are-coming-lots-questions

Update 9/2/22

Some answers to commonly asked questions can be found in the Stat article.

On Thursday evening, Centers for Disease Control and Prevention Director Rochelle Walensky signed off on the recommendation made earlier in the day by the Advisory Committee on Immunization Practices, that the newly formulated vaccines be used.

Your questions on the new Covid vaccine boosters answered — https://www.statnews.com/2022/09/01/your-questions-on-the-new-covid-vaccine-boosters-answered/