By Jennifer Rigby and Manas Mishra (Reuters) – Figures showing a global rise in COVID-19 cases could herald a much bigger problem as some countries also report a drop in testing rates, the WHO said on Tuesday, warning nations to remain vigilant against the virus. After more than a month of decline, COVID cases started to increase around the world last week, the WHO said, with lockdowns in Asia and China’s Jilin province battling to contain an outbreak. A combination of factors was causing the increases, including the highly transmissible Omicron variant and its BA.2 sublineage, and the lifting…