Some blood tests being marketed to tell people if they have had the new coronavirus are a “disaster”, Roche Chief Executive Severin Schwan said on Wednesday as he prepares to launch the drugmaker’s own antibody test next month.

Countries around the world hope such blood tests – meant to show whether people exposed to the disease have developed antibodies thought to offer some immunity – will guide efforts to restart their economies and keep healthcare workers safe.

An erroneous false-positive result could lead to the mistaken conclusion that someone has immunity. In developing its test, Schwan said, Roche scrutinised some existing products for reliability before rejecting them.

“It’s a disaster. These tests are not worth anything, or have very little use,” Schwan told reporters on a conference call. “Some of these companies, I tell you, this is ethically very questionable to get out with this stuff.”

Schwan said there were about 100 such tests on offer, including finger-prick assays that offer a quick result. The Basel-based company declined to specify which rival tests it had studied, but said it was not referring to tests from established testing companies.

Roche also makes separate tests to determine if a person has an active coronavirus infection, with a sample taken via a swab from nasal passages.

By contrast, Roche’s planned antibody test relies on intravenous blood draws taken by a nurse or a doctor.

Schwan did not release figures for its test’s “specificity”, or how many false-positives can be expected, but promised it would be reliable because Roche had successfully found the antibody produced by the body after exposure to the novel virus.

Abbott Laboratories also said last week it would begin shipping a new coronavirus blood test similar to Roche’s by June. Like Roche’s test, Abbott’s assay would be launched under the U.S. Food and Drug Administration’s recently relaxed rules for coronavirus tests.