According to a study published in the Lancet, the Pfizer COVID-19 vaccine appears to be less effective against the Delta variant, which is dominating in India, compared to the original version of the coronavirus. 

It further noted that the antibody response to variants is even lower in individuals who have been administered only one dose of the vaccine. Additionally, a longer gap between the two doses may cause a significant reduction in antibodies against the Delta variant.

Following a single dose of the Pfizer COVID-19 vaccine, 79%of the individuals had measurable neutralizing antibody response against the original strain, which dropped to 50% for the B.1.1.7 or Alpha variant, 32% for Delta variant and 25% for the B.1.351 or Beta variant first found in South Africa… (NDTV, June 4, 2021)