A team of scientists in India has developed an inexpensive paper-based test for coronavirus that could give fast results similar to a pregnancy test. The BBC's Soutik Biswas and Krutika Pathi unpack how it works.

The test, named after a famous Indian fictional detective, is based on a gene-editing technology called Crispr. Scientists estimate that the kit - called Feluda - would return results in under an hour and cost 500 rupees (about $6.75; £5.25).

Feluda will be made by a leading Indian conglomerate, Tata, and could be the world's first paper-based Covid-19 test available in the market.

"This is a simple, precise, reliable, scalable and frugal test," Professor K Vijay Raghavan, principal scientific adviser to the Indian government, told the BBC.

Researchers at the Delhi-based CSIR-Institute of Genomics and Integrative Biology (IGIB), where Feluda was developed, as well as private labs, tried out the test on samples from about 2,000 patients, including ones who had already tested positive for the coronavirus.

They found that the new test had 96% sensitivity and 98% specificity. The accuracy of a test is based on these two proportions. A test that's highly sensitive will detect almost everyone who has the disease; and a test that has high-specificity will correctly rule out almost everyone who doesn't have the disease.

The first ensures not too many false negative results; and the second not too many false positives. India's drug regulator has cleared the test for commercial use.

With more than six million confirmed infections, India has the world's second-highest Covid-19 caseload. More than 100,000 people in the country have died of the disease so far.

After a slow start, India is now testing a million samples a day in more than 1,200 laboratories across the country. It is using two tests.

Source: BBC