An AstraZeneca plant in Wales was evacuated and the bomb disposal unit called after a "suspicious package" was found.
The industrial estate where the Oxford University/AstraZeneca vaccine is put into vials and syringes was partially evacuated while the package was investigated.
Wockhardt UK, the company that operates the site, said in a statement: "Wockhardt UK in Wrexham this morning received a suspicious package to site. All relevant authorities were immediately notified and engaged.
"Upon expert advice we have partially evacuated the site pending a full investigation. The safety of our employees and business continuity remain of paramount importance."