Some women are experiencing menstrual adverse events (AEs), including heavier bleeding, following the coronavirus disease 2019 (COVID-19) spike immunization. The etiology of these menstrual AEs associated with the COVID-19 spike immunization remains unknown. The United States Department of Health and Human Services Vaccine Adverse Event Reporting System (VAERS) database was retrospectively analyzed for data-reported AEs affecting menstrual cycles by vaccine. Elevated normalized frequencies for menstrual AEs were detected for multiple vaccines, including COVID-19 vaccines (Pfizer BioNTech: 4,442, Pfizer BioNTech bivalent: 686, Moderna: 2,038, and Moderna bivalent: 463, all/100,000 VAERS reports) and human papillomavirus (HPV) vaccines (HPV Cervarix: 6,090, HPV Gardasil: 2,959, and HPV Gardasil 9: 1,556 all/100,000 VAERS reports). Lower normalized frequencies were detected for both COVID-19 bivalent vaccines and the HPV Gardasil 9 vaccine, compared to higher normalized frequencies for COVID-19 Pfizer-BioNTech, COVID-19 Moderna, HPV Cervarix, and HPV Gardasil vaccines. χ² (2 × 2) statistically significant differences in normalized frequencies were observed between different COVID-19 Pfizer-BioNTech lots (p<0.00001) and also COVID-19 Moderna lots (p<0.00001). Manufacturing contaminants (e.g., endotoxins) are likely candidates, consistent with the observed data, for the reported menstrual AEs that vary by vaccine version and batch lot.