Ersboell quit to join Chandler Chicco Agency’s sister firm Biosector 2, where she started this week in the newly created role of London office managing director.
MS&L managing director Nicholas Walters said he expected to have appointed a replacement by next month.
At Biosector 2 Ersboell - who reports to principal Bob Chandler - said her appointment would trigger a push for new business in continental locations, including Germany and her native region of Oresund, which covers Denmark and Sweden.
Ersboell said she aimed to win new business in fields such as the research and development of innovative therapeutics, services and devices.
‘Biosector 2 is about more than biotech - it’s about anything to do with innovation in healthcare,’ she added.
Prior to MS&L, where she had worked for 18 months, Ersboell spent 13 years at Burson-Marsteller - her last role there being MD of the Nordic healthcare practice.
Biosector 2 was set up in July last year. It has five staff in London and ten in New York.
Meanwhile, former Citigate Dewe Rogerson international MD Kevin Soady has re-emerged two years after quitting the City PR agency to join rival Capital MS&L.
Soady - one of the original Dewe Rogerson directors who saw through the sale of the agency to Incepta’s Citigate Communications five years ago - becomes a director at Capital.