It is unclear exactly how the headdress, made of hundreds of long quetzal feathers and more than 1,000 gold plaques, ended up in Austria, where it is on display at a museum in Vienna.
The pause means the online enrollment system has been closed for the 60,000-patient clinical trial while the independent patient safety committee is convened.
The authorities said the emergency shelters had been sanitized to prevent the spread of the coronavirus, which has killed more than 81,000 people in Mexico and battered the key tourism industry.