BERLIN - The head of the World Health Organization acknowledged it was premature to rule out a potential link between the COVID-19 pandemic and a laboratory leak, and he said Thursday he is asking China to be more transparent as scientists search for the origins of the coronavirus.In a rare departure from his usual deference to powerful member countries, WHO Director-General Tedros Adhanom Ghebreyesus said getting access to raw data had been a challenge for the international team that traveled to China earlier this year to investigate the source of COVID-19.