The Sandia National Laboratories in Albuquerque, N.M., was preparing Monday to move some of its workforce back on site, even as the host counties for two other Department of Energy facilities in the state faced new difficulties from the COVID-19 pandemic.

Of the two DoE nuclear weapons laboratories in New Mexico, Sandia has been locked down the longest. The lab urged any employees who could to start teleworking the week of March 16. Albuquerque and the surrounding Bernalillo County have been hard hit by COVID-19, with the county posting more than one-third of New Mexico’s 686 confirmed cases, and more than half the state’s fatal infections.

But as of Monday, a spokesperson for the weapons-engineering lab confirmed, Sandia had reopened its Ion Beam Laboratory in Building 720, which had to be locked down and disinfected after someone there tested positive for COVID-19. That is one of at least three confirmed cases at Sandia’s Albuquerque site.

“All employees who have confirmed contact with the individual who tested positive have been contacted by the Sandia Medical Clinic for further instructions,” Sandia wrote in a post on its website. About 70% of the lab’s workforce of 14,000 or so had been teleworking, as of last week. Including the lab’s California campus, Sandia has at least seven cases.

The Ion Beam Laboratory can subject materials to stresses similar to what they would experience if bombarded with neutrons. That can help test new materials intended for nuclear applications.

Los Alamos County, home to the national laboratory of the same name, announced this weekend it had logged its first confirmed cases of COVID-19, which is caused by the novel coronavirus that broke out in Wuhan, China, last year. Los Alamos was, until this month, the only host county of a National Nuclear Security Administration nuclear-weapon lab that had not reported at least one confirmed case. Los Alamos County had at least two cases, at deadline Tuesday.

Further south, in Eddy County, someone died after contracting the virus, according to data tracked by Johns Hopkins University. Eddy County includes the city of Carlsbad, home to DoE’s Waste Isolation Pilot Plant (WIPP). The county has also been abuzz with oil-field workers over the past several years.