Vaccination certainly can be an effective tool to fight disease. In some cases, such as with polio or measels, it's our best tool that we have.
a) Not all vaccines have equal effectiveness. Just because something is called a vaccine doesn't mean it has the capability to end transmission of a pathogen. There is ample evidence that our current vaccines effectiveness is limited in preventing transmission of Covid, with studies ranging from 40%-80% for prevention of delta.
b) Covid mutates much more quickly than polio. Just like flu shots, vaccines have limited effectiveness due to the variations within the virus. Even with 100% uptake of the current available vaccines, transmission and mutation will continue.
LONDON — Achieving herd immunity with Covid vaccines when the highly infectious delta variant is spreading is “not a possibility,” a leading epidemiologist said.
Experts agree on several reasons why such a goal — where overall immunity in a population is reached and the spread of the virus is stopped — is not likely.
Sir Andrew Pollard, head of the Oxford Vaccine Group, told British lawmakers Tuesday that as Covid vaccines did not stop the spread of the virus entirely — with vaccinated people still able to be infected and transmit the virus — the idea of achieving herd immunity was “mythical.”
“I think we are in a situation here with this current variant where herd immunity is not a possibility because it still infects vaccinated individuals,” said Pollard, one of the lead researchers in the creation of the AstraZeneca-University of Oxford vaccine.
Herd immunity is 'mythical' with the Covid delta variant, expert says (cnbc.com)