The Health Unlimited business in the US, which includes specialist consultancy Corkery Group, will be rebranded as M Booth Health and operate as a separate agency, reporting to M Booth CEO Dale Bornstein. M Booth Health will have a workforce of around 50 people.
Timothy Bird, CEO of Health Unlimited, will continue to lead the agency alongside his US-based management team.
The UK division of Health Unlimited will remain with Unlimited Group, the London-based owner of Nelson Bostock Unlimited and Fever Unlimited.
MBooth Health has clients across medical device suppliers, pharmaceutical firms, government agencies, medical societies, advocacy organisations and consumer health organisations. The price of the deal has not been disclosed.
Next 15 CEO Tim Dyson said: "The acquisition is a major milestone for Next 15 as it adds another specialist business to the portfolio and greatly expands our international footprint in the healthcare sector. We see significant complementary opportunities for both businesses."
Bird said: "We believe there are significant synergies between both organisations and these complementary strengths will allow us to shape new offerings for clients in areas such as creative, content, digital, influencer, analytics and public affairs. The collaboration allows us to offer our talented teams new opportunities for career growth."
In April, Unlimited Group announced the acquisition of B2B marketing agency DirectionGroup, since rebranded as DirectionGroup Unlimited. It was Unlimited Group’s third acquisition this year, following content marketing specialist First Base (now First Base Unlimited) and data and analytics agency Model Citizens (now Realise Unlimited).
Meanwhile, Next 15 has reported a 14 per cent rise in adjusted pre-tax profit to £17.2m in the first half of 2019, as net revenue rose 11 per cent to £118.7m.
Organic revenue fell 1.3 per cent in the half year. The company cited the restructuring the Archetype - the PR agency created by the merger of Text100 and Bite earlier this year - and the loss of Samsung and Just Eat as clients at its agency Beyond.
However, Next 15 increased its interim dividend by 15.7 per cent to 2.5p per share and said it "remains optimistic about the medium term outlook" and is "confident of a return to high single digit organic growth in the next financial year".
Chairman Richard Eyre said: "Next 15 continues to make good progress, validating our strategic focus on marketing technology as our Data and Analytics based businesses lead our growth.
"With the acquisition of Health Unlimited announced today, we are confident of meeting our expectations for this year. Furthermore, we are increasingly confident about our next fiscal year as the changes at Archetype and Beyond work through alongside the full year impact of our more recently acquired businesses."