What are BA.4 and BA.5 sub-variants of Omicron, and can they lead to a Covid surge in India?

The European CDC is anticipating a significant overall increase in Covid-19 cases in the coming weeks and months due to the BA.4 and BA.5 sub-variants of Omicron. What are these new strains, and could they trigger a fourth wave in India as well? The European Centre for Disease Control and Prevention has declared the BA.4 and BA.5 sub-variants of Omicron as ‘variants of concern’. Being sub-variant of Omicron, the World Health Organisation (WHO) already considers both to be ‘variants of concern’. Can the two new sub-variants lead to another wave of Covid-19 in the country? Can previous infections and high levels of vaccination protect against severe disease and hospitalisations?