With an increase of about 65,000 cases in 24 hours, India's Covid-19 tally crossed the 25-lakh mark on Saturday. Close to 1,000 deaths were also reported within the span of a day. There are now total 25,26,196 cases in the country, including 6,68,220 active cases, 18,08,937 discharged/migrated and 49,036 deaths. Prime Minister Narendra Modi, addressing the nation on Independence Day, said that the country's scientists were working day in and out - "like Rishi, Munis' - to develop a vaccine against Covid-19.

The number of active cases in Maharashtra, the worst-hit state by the pandemic stands at 1,51,865, while 4,01,442 patients have recovered in the state. The toll due to the disease is presently 19,427 in the state.

Active cases in Tamil Nadu stands at 53,716, while 2,67,015 patients have been cured and the disease has claimed 5,514 lives in the state.

In Andhra Pradesh, there 89,907 active cases while 1,80,703 patients have been cured so far. The infection, however, has led to the death of 2,475 patients.

In Delhi, there are 11,366 active cases and 1,35,108 recovered patients. The toll due to the disease stands at 4,178.

US scientists are developing a strain of the coronavirus that could be used to deliberately infect volunteers in so-called "challenge studies," a government agency said Friday. The work is preliminary and the government is continuing to prioritize randomized clinical trials of vaccine candidates, the National Institute for Allergies and Infectious Diseases (NIAID) said. Several of these have entered their final stages, including the vaccines developed by Moderna, Pfizer and AstraZeneca. But NIAID has nonetheless "begun efforts to manufacture a strain that could be used to develop a human challenge model, if needed," it said in a statement. In normal clinical trials, volunteers receive either a medicine or a placebo and their health is then followed over the course of months of years.