Aug 27 (Reuters) - More than half of U.S. companies are planning to impose COVID-19 vaccine mandates in the workplace by year end, with almost a quarter considering vaccination as a condition for employment, according to a national survey of nearly 1,000 employers. In the face of a resurgence in COVID-19 cases, spurred by the highly contagious Delta coronavirus variant, that has strained the U.S. health care system, many companies have come out with mask mandates and changed their vaccination policies. Google"s parent Alphabet Inc (GOOGL.O), Walmart Inc (WMT.N), and Goldman Sachs Group Inc (GS.N) are among the growing list of employers requiring some or all staff to get the vaccine. read more The survey, which polled 961 U.S. companies that together employ around 9.7 million people, found that by the fourth quarter of 2021, over 52% of employers could have one or more vaccine mandate requirements, an increase from 21% currently. The mandates could range from requiring vaccination for staff to access common areas such as cafeterias to requiring vaccination for all employees, according to the survey conducted by Willis Towers Watson between Aug. 18 and 25. Last week, the U.S. Food and Drug Administration granted full approval to the Pfizer Inc (PFE.N)/BioNTech SE COVID-19 vaccine, an important step that could help accelerate vaccine mandates in the United States. "We expect even more employers to institute vaccine mandates in the wake of FDA approval of the Pfizer vaccine," Willis Towers Watson"s population health leader, Jeff Levin-Scherz, said. The survey found the number of employers that track whether employees have completed their vaccination was increasing, with more companies considering implementing financial incentives for vaccinations. About 62% of the U.S. population has received at least one dose, while more than half or roughly 52% are fully vaccinated against COVID-19 as of Tuesday, according to the Center for Disease Control and Prevention.