A third wave of the coronavirus is "inevitable", the government's top scientific adviser said on Wednesday, warning that vaccines will need to be "updated" to deal with the new strains that have sped up the contagion in India, overwhelming hospitals and killing thousands. "Phase 3 (third wave) is inevitable, given the high levels at which this virus is circulating. But it is not clear at what time scale this Phase 3 will occur. Hopefully, incrementally, but we should prepare for new waves. Ongoing surveillance is needed as are vaccine upgrades," Dr K VijayRaghavan said at a government briefing.