Another question - is there statistics on how many people take part in these mass events?
By the way, if you look at the same Brazil, you will notice that between the carnival in 2020 (March 2020) and the beginning of a noticeable increase in the disease, the same approximately 1.5 months can be traced (May 2020).
I will add another example from life - despite the fact that in Ukraine there are not a full 40 million people, but in the capital there are about 4 million people, this is absolutely not commensurate with the population of India, but as soon as, after the new year, many decided that "the disease is controlled ", and began mass visits to shopping centers, cinemas, restaurants, pubs, etc. - after 1.5 months we received a "result" - a noticeable surge and an increase in the detection of new diseases. True, at first we pretended that everything was fine, and then realized that we were on the verge of a new explosion of the disease, and introduced another quarantine in many regions of the country, including the capital.
I will also add that the period is 1-1.5 months, this is exactly the period when a critical mass of carriers and primary cases is formed, after which an explosive growth of the disease begins, this is quite consistent with the model of the spread of the virus.
I had also explored about the possibility of a spike created as a result of the Holi celebrations. But my contacts vehemently deny that it is possible. One factor that they point out is that there was absolutely no spike after the new year celebrations (the number of cases on the contrary went down in January). I know that new year celebrations are quite big in India and there was no social distancing or government restrictions at that point of time. The situation was quite relaxed back then. Then suddenly during the first week of April, the cases started exploding all of a sudden.
One explanation that I have heard is about the UK strain. In India, it was first reported from the state of Punjab. Then it spread to other states in North India. I don't think that Holi was the trigger, because it is not celebrated in South India. However, the recent wave impacted South Indian states as well.