According to a study conducted by the National Institute for Occupational Safety and Health, which was first reported by Business Insider, a majority of imported masks — nearly all of which were manufactured in China — may not function as intended or adequately protect health care workers from infection with the coronavirus.

According to the report, researchers from NIOSH tested imported masks that were made by 67 different companies, and concluded that almost two-thirds of them do not block 95% of all particles from the air. Many of the masks that were tested performed abysmally, blocking less than half of all air particles at their maximum efficiency, meaning that they are actually less effective at blocking particles than the very cheapest cloth masks available on the market.

Based upon the names of the companies whose masks were tested, the vast majority of the tested masks were manufactured in China. The problem of defective Chinese masks has been noted before. European officials sounded the alarm weeks ago that the vast majority of masks manufactured in China were defective and did not perform as advertised.

It should be noted that some of the Chinese companies produced masks that were apparently quite good, registering above 99% at both maximum and minimum efficiency. Some, however, were barely better than having no face covering at all. For example, masks manufactured by Anhui RYZUR Medical Equipment Manufacturing Co., Ltd. blocked only 33.9% of particles at maximum efficiency and an abysmal 27% of particles at minimum efficiency.

Even before these tests were performed, U.S. officials stated that they suspected that many of the imported N95 masks were not functioning properly, but felt that they had no choice other than to use them due to a worldwide shortage of the masks.