North Korea is casting doubt on the efficacy of COVID-19 vaccines as its economy continues to flail under the pandemic and as the country keeps up a ban on most international travel.

On Tuesday, North Korean state media warned its people of potential side effects from COVID-19 vaccines developed abroad and urged the public to continue to abide by the state’s protective measures for fear of “catastrophic consequences.” These measures include wearing masks, social distancing and regularly sanitizing hands in the workplace.