Then why are vaccinated people still contracting the disease?
Well, none of the four COVID-19 vaccines available worldwide can provide complete protection against infection. Yes, vaccines train our antibodies to block or neutralize the COVID-19 virus, this being the key defense against the spread of the virus, but each individual reacts differently to vaccination.
Therefore, there will be a wide variation in the amount and quality of the antibodies every one of us will generate after receiving the vaccine. According to scientists, some of the vaccinated individuals may not produce sufficient antibody levels in their upper airways to counter a delta infection early enough to stop it from replicating further.