Fifty-five people in the United States have died after receiving a COVID-19 vaccine, according to reports submitted to a federal system.

Deaths have occurred among people receiving both the Moderna and the Pfizer-BioNTech vaccines, according to the reports.

The reporting system, the Vaccine Adverse Event Reporting System (VAERS), is a federal database. The system is passive, meaning reports aren’t automatically collected and must be filed. VAERS reports can be filed by anyone, including health care providers, patients, or family members.

VAERS reports “often lack details and sometimes can have information that contains errors,” according to the reporting system’s website. Still, reports on VAERS represent “only a small fraction of actual adverse events,” the site states, though under reporting is believed to be less common for serious events.