A recent study revealed that a full 98% of hospital staff workers in northeastern France who contracted mild cases of COVID-19 developed protective antibodies.

Researchers at Institut Pasteur examined 160 doctors and nurses who were treating patients with the disease and became infected, and found that only one did not develop the antibodies that experts hope can neutralize the virus. The volunteers for the study developed antibodies within 41 days of having symptoms.

According to The Hill, antibody testing has been widely used to help countries reopen safely, although the World Health Organization warned last month that there is no evidence that those who recover from COVID-19 and develop antibodies are actually immune to the disease.

“This finding supports the use of serologic testing for the diagnosis of individuals who have recovered from SARS-CoV-2 infection,” said the study authors in their research paper, according to Bloomberg.