Sept 9 (Reuters) - Microsoft Corp (MSFT.O) said on Thursday it will no longer target a specific date for reopening all of its U.S. offices and instead will reopen each site based on whether it meets a set of company criteria and local health guidelines. "Given the uncertainty of COVID-19, we"ve decided against attempting to forecast a new date for a full reopening of our U.S. work sites in favor of opening U.S. work sites as soon as we"re able to do so safely based on public health guidance," Microsoft said in a blog post. Microsoft had earlier said it would open its Redmond headquarters as well as other U.S. offices on Oct. 4. Microsoft on Thursday said each U.S. site will return to work when all local government guidelines are met and when the site has reached "Stage 6" of a set of criteria the company detailed in March. Hitting the sixth stage requires that "COVID-19 is no longer a significant burden on the local community and presents itself more like an endemic virus such as the seasonal flu," Microsoft said in an earlier blog post. Some big tech firms are delaying a return to office, while others like Facebook Inc (FB.O) are making vaccinations mandatory due to the spike in COVID-19 cases in the country. read more The software giant said it will also give a 30-day transition period that provides time for employees to prepare before getting back to offices.