Are variants driving the surge in cases?
It's hard to say. The WHO says more study is urgently needed. Laboratory-based studies of limited sample size suggest potential increased transmissibility, it concluded. The picture is complicated because the highly transmissible B.117 variant first detected in the U.K. is behind spikes in some parts of India. In New Delhi, UK variant cases almost doubled during the second half of March, according to Sujeet Kumar Singh, director of the National Centre for Disease Control. The Indian variant, though, is widely present in Maharashtra, the country's hardest-hit state, Singh said.
Prominent U.S. disease modeller Chris Murray, from the University of Washington, said the sheer magnitude of infections in India in a short period of time suggests an "escape variant" may be overpowering any prior immunity from natural infections in those populations.