New Delhi: Fifty more deaths took the swine flu toll close to the 1,600-mark with nearly 28,000 people affected even as a study by the US-based MIT suggested that the H1N1 virus may have acquired mutations which make it more "severe and infectious".

The Union Health Ministry today said that as on March 11, the swine flu toll in the country had reached 1,587 while the number of cases of the disease stood at 27,886. As the swine flu onslaught continues unabated, four more persons succumbed to the disease in Rajasthan, where the toll, according to state health officials, has reached 358.