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Are you sure about this? Because I just read a journal article which claims that the Pfizer vaccine produces 5 times less antibodies while coming in to contact with the Delta (B.1.617.2) strain. That doesn't mean that the Pfizer vaccine will be ineffective against the mutant strain, but there is a strong chance that it will be "less effective". And in due course of time, we will see more mutant strains, against which the efficacy of the vaccines will be even lower. Vaccine manufacturers need to deal with this issue.
Full text here:
https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)01290-3/fulltextThat's because Pfizer vaccine is an mRNA vaccine that works differently with other vaccines. They instruct the cells to create a spike immune response to prevent the virus from latching on the cells. Antibodies aren't produced by vaccines, they are produced by the host and they will only be produced for a specific one if a specific virus have been introduced to the body albeit in a weak state.