Health insurer Aetna's proposed $37 billion acquisition of smaller rival Humana Inc was approved by the shareholders of both companies.
The companies continue to expect the deal to close in the second half of 2016, they said in separate statements on Monday.
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Aetna in July said it would buy Humana to become the largest provider of Medicare plans for the elderly.
Three weeks later, rival Anthem Inc proposed to acquire Cigna Corp for about $47 billion in a deal that would make it the largest U.S. health insurer by membership.
The proposed mergers follow the implementation of President Barack Obama's healthcare overhaul, the Affordable Care Act, which extended health insurance to millions of people.
Insurers say joining forces will help them better compete as the government tries to rein in healthcare spending.
However, federal antitrust authorities are expected to closely scrutinize these proposed deals for potential harm to consumers.
(Reporting by Natalie Grover in Bengaluru; Editing by Savio D'Souza)