Nations that store possible COVID-19 vaccines while not sharing them with others will deepen the pandemic, the head of the World Health Organization (WHO) said on Tuesday. The WHO’s chief, Tedros Adhanom Ghebreyesus, appealed to countries to join an international agreement on vaccines. The WHO has urged wealthier nations to join its “COVAX Global Vaccines Facility” for sharing possible vaccines with developing nations. Tedros said he sent a letter to the WHO’s 194 member states, telling them to sign up for the program by August 31.