An early warning system to monitor vaccine safety, established by the government more than 30 years ago, has been at the center of federal efforts to develop and distribute vaccinations against Covid 19. But data collected by the system, known as VAERS, for Vaccine Adverse Event Reporting System, has also been manipulated and misused to spread false information during the pandemic.

VAERS, managed by the Centers for Disease Control and Prevention and the Food and Drug Administration, collects raw, unverified reports of vaccine effects from patients and health care providers. Those reports are entered immediately into a database, then later analyzed for accuracy and severity. That two-step process leaves room for misinterpretation, according to Seth Mnookin, a professor at M.I.T. and author of “The Panic Virus.”

“Anyone can file a report,” Mnookin said in an interview with Retro Report. “I can. You can. Doctors are required to. So if my child gets vaccinated today and then, on the way home, trips and breaks his leg, I can file a report saying my child got a pertussis vaccine, then he broke his leg.”

Such a report could be misleading, Mnookin said.

“In this database, there will be a line saying: Pertussis vaccine, broken leg. That does not mean that A caused B. It means someone reported it,” Mnookin said. “But vaccine opponents will use that and say – Here is a federal database in which there’s a line saying that this vaccine causes this reaction.”

Scientists believe VAERS is an important tool to collect information about vaccines, but its data has frequently been misused. The F.D.A. website warns that VAERS reports “generally cannot be used to determine if a vaccine caused or contributed to an adverse event or illness.”

Rep. Marjorie Taylor Greene cited the system on Twitter before she was banned this month for violating the platform’s rules on sharing Covid-19 misinformation. Tucker Carlson provided false information in May on the Fox News show he hosts; he too based his claims on information from VAERS.

The roots of federal regulation of vaccines reach to 1955, following the Cutter Incident, when 10 people died and about 200 more were paralyzed after receiving the Salk polio vaccine. Certain lots of the vaccine, produced by Cutter Laboratories in California, contained virus that had not been inactivated. A judge ruled that the manufacturer had not been negligent, but was financially responsible for the harm its vaccine caused.

Then, starting in the 1970s, the number of lawsuits over vaccine safety increased, with large jury awards driving many pharmaceutical companies out of vaccine manufacturing. For example, by the end of 1984, only one U.S. company manufactured the diphtheria-pertussis-tetanus vaccine.

In 1986 Congress passed the National Childhood Vaccine Injury Act, which contained a program to compensate individuals harmed by certain vaccines that were manufactured in accordance with federal government standards. The legislation also provided for a reporting system for vaccine-related adverse events. In 1990, the C.D.C. and F.D.A. introduced a new tool to help public health agencies identify vaccine results – the Vaccine Adverse Event Reporting database.

BONNIE BERTRAM is a senior producer at Retro Report.This article first appeared in Retro Report’s free weekly newsletter. Subscribe and receive lessons from history in your mailbox. Follow us on Twitter @RetroReport.