>. . Preliminary tests conducted by Pfizer in June 2022 were done on eight mice. The actual number of mice involved in the recent trials is unclear. >Data provided by Pfizer to the CDC on Tuesday indicated trials involving female mice, 10 per group, were provided a primary series of monovalent vaccine, a third booster dose of the bivalent (original vaccine plus BA.4/5) vaccine, and then a fourth booster dose of either a bivalent (original plus BA.4/5) or a monovalent (XBB.1.5) vaccine. >A spokesperson for Pfizer referred Newsweek to the data it presented to the CDC on Tuesday, declining to comment otherwise. Newsweek also reached out to the FDA, CDC, and Moderna via email for comment. . . [Source Article](https://www.newsweek.com/covid-booster-tested-mice-what-we-know-1826701?amp=1)