Some vaccine recipients can develop serious adverse events (SAEs) following coronavirus disease 2019 (COVID-19) immunization. In a retrospective study of the Vaccine Adverse Event Reporting System (VAERS) menstrual AEs following immunization, statistically significant differences were observed for multiple manufacturing lots of the COVID-19 Pfizer–BioNTech and the COVID-19 Moderna vaccines.  Other candidate manufacturing contaminants associated with AEs may be detectable by comparing normalized frequency rates between predicted higher-contamination lots or vaccines and lower-contamination lots or vaccines. This retrospective study identified candidate pattern signatures for the most frequently reported AEs in VAERS for identified COVID-19 vaccine lots associated with these menstrual AEs, as well as differences in AE frequencies between three human papillomavirus (HPV) vaccines. Six candidate AE patterns (AEPs) were identified: hemorrhage (female), gynecologic including hemorrhage pattern, myopericarditis (male-biased), HPV vaccine-associated, neuropathy, and fetus patterns.  The hemorrhage pattern was identified in six vaccines, including four influenza vaccines.  The gynecologic pattern was identified in seven vaccines, including three COVID-19 and three HPV vaccines.  The myopericarditis pattern was identified in 14 vaccines, including five COVID-19 vaccines, with two bivalent COVID-19 vaccines and three smallpox vaccines. The myopericarditis pattern appears to be associated with possible contaminant microbial protein activation of immune responses and live attenuated virus vaccines.  The four AEP_HPV AEs were elevated primarily among HPV vaccines. One or more of the five AEP_neuropathy AEs were elevated in 11 vaccines, while one or more of the AEP_fetus AEs were elevated in 11 vaccines.