This study used data from VAERS, which only collects adverse effects of vaccines, including the mfg, lot, severity of injury, etc. The "died suddenly" may be included here, but if they're not identified as a vaccine death, they probably aren't. VAERS was built to document acute vaccine injuries and deaths like seizures and paralysis, not the longer term deaths that aren't "recognized." VAERS is considered to represent only about 1% of true vaccine injuries and deaths because of the reporting process. I suspect that the "died suddenly" numbers don't come from the bad 5%, but from the cumulative effects of boosters.