Ludwig Hantson (C), Chief Executive Officer of Baxalta, celebrates the company's IPO after ringing the opening bell above the floor of the New York Stock Exchange, July 1, 2015.Reuters

Drugmaker Shire Plc announced on Monday that it finally struck a deal to acquire Baxalta International Inc in a cash and stock deal worth $32 billion after a six-month long pursuit.

The mega deal in the pharma sector marks a strong beginning for the mergers and acquisitions activity in the global healthcare industry in 2016 as it's said to create the world's biggest rare-disease drugmaker.

"This proposed combination allows us to realize our vision of building the leading biotechnology company focused on rare diseases. Together, we will have leadership positions in multiple, high-value franchises and become the clear partner of choice in rare diseases. Our expanded portfolio and presence in more than 100 countries will drive our growth to over $20 billion in anticipated annual revenues by 2020," said Shire Chief Executive Officer Flemming Ornskov in a statement.

Following the deal, the combined effective tax rate of Shire and Baxalta would drop to 16% to 17% by 2017 compared to the current rate of 23.5% paid by Baxalta in the US.

The Dublin-based Shire's acquisition of US-based Baxalta comes at a time when the inversion deals made by the US pharma companies are being criticised as their bids to avoid 35% corporate tax rate in the country, which is among the highest in the world.

"The deal proves that a new year can't hide the flaws of our outdated tax code," the WSJ quoted US Senator Rob Portman (R., Ohio) as saying. "If we want to keep U.S. businesses, jobs and investment in the U.S., tax reforms must be a 2016 priority."

In November last year, US-based Pfizer Inc had bought Botox-maker Allergan Plc in a deal worth $150 billion. The inversion deal was expected to help Pfizer to redomicile to Ireland, where the headquarters of Allergen is situated, enabling it to cut its corporate tax payment in the US.

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