As soon as the coronavirus pandemic began, workers across the country flooded federal and state offices with complaints that their employers werent protecting them from the health threat. The concerns have continued to pour into workplace safety agencies for seven months, totaling nearly 40,000 as of Thursday.

It turns out the allegations have been a flashing warning sign all along, according to a new working paper published by the Harvard Center for Population and Development Studies . The analysis of data from the Occupational Safety and Health Administration shows that a rise in workers safety complaints has preceded a rise in deaths throughout the pandemic.

Experts looked at complaints filed with OSHA and corresponding state agencies from February to late August, and set the data against fatalities likely caused by the novel coronavirus. What they found was that the curve of the complaints roughly matches the curve of pandemic deaths, with the latter trailing the former by 17 days.

Nancy Krieger, a professor of social epidemiology at Harvard University, said the lag in the time when the deaths occur is a key finding. Workers likely became aware of infections happening around them, felt they werent protected on the job and tried to blow the whistle. Then, within a couple of weeks, the number of deaths was increasing.

Its not that there were deaths and then people started complaining, Krieger said. There were [safety] complaints and then the deaths happened.