Global COVID-19 cases declined last week for the third week in a row, but cases are rising in some countries, the head of the World Health Organization (WHO) said today, urging nations to keep their guard up, especially with the threat of variant viruses.Push for vaccine teamwork, vigilanceAt a briefing today, WHO Director-General Tedros Adhanom Ghebreyesus, PhD, said the drop in cases is encouraging, because it shows that the virus can be controlled, even with new variants circulating that are thought to be more transmissible."However, we have been here before," he warned, referencing declines after earlier surges when some countries opened up too quickly, allowing people to let their guard down and COVID-19 levels to soar again.Tedros