In the UK the Delta variant seems to have followed a similar curve to India: sharp increase followed by sharp fall. The Indian peak was around the begining of May, the UK around the 20th of July. ONS estmates 91.9% of adult UK population have antibodies (both figures are current not at start of curve). In India it's about 67% of population has antibodies. It is not known why the steep fall in cases happened in India. If the patterns are as similar as they appear we can, perhaps, rule out schools and other factors not common to the 2 countries.
It coincided in India with rollout of prophylactic ivermectin. While the studies we have for prophylactic ivermectin aren't well powered, they suggest that prophylactic ivermectin reduces COVID-19 infection by an average 86% (95% confidence interval 79%–91%) which works well to explain what we see in India.
In the UK the Delta variant seems to have followed a similar curve to India: sharp increase followed by sharp fall. The Indian peak was around the begining of May, the UK around the 20th of July. ONS estmates 91.9% of adult UK population have antibodies (both figures are current not at start of curve). In India it's about 67% of population has antibodies. It is not known why the steep fall in cases happened in India. If the patterns are as similar as they appear we can, perhaps, rule out schools and other factors not common to the 2 countries.