NEW DELHI : The fourth wave of the COVID-19 pandemic in Delhi is causing high-grade fever, spreading faster and affecting the younger population, especially those in the age group of 30 to 50, more, according to experts.Delhi Chief Minister Arvind Kejriwal has said the fourth wave is more dangerous than the previous ones and according to data available with him, 65% of patients infected this time are below 45 years.The sudden spike in COVID-19 cases in Delhi over the last few days and across the country has baffled medical experts.Some doctors said the reason behind a large number of people contracting the infection this year vis-a-vis last year could be that the "virus has mutated" and the current strain is more infectious."The younger.