Delta variant and the (im)possibility of Herd Immunity...?

A quick chart on the situation in the UK, which has one of the highest vaccination rates, where the mRNA and AZ vaccines make up the majority of doses given.

Source: https://ourworldindata.org/covid-vaccinations?country=OWID_WRL

Note that most of the new cases are reportedly among the young unvaccinated....  

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The Delta variant has taken hold in Britain despite almost 62% of adults being fully vaccinated, a slightly higher rate than in the U.S.  Most of the new cases are in younger people who've yet to have the two doses needed for maximum protection.

And of course, it isn't just in the UK where the Delta variant is becoming a problem....

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But in countries like Russia and Indonesia, where vaccination rates are much lower, the new strain is already being blamed for overwhelming hospitals and filling cemeteries.  In Australia, where tough border controls helped to keep cases in check over the last year and a half, officials just imposed a strict two-week lockdown on Sydney as infections mount.  CBS News' Elaine Cobbe in Paris reported on Tuesday that the Delta variant now accounts for one in five new COVID-19 cases in France — a similar proportion to that seen in the U.S.

Source for quotes: https://www.cbsnews.com/news/delta-variant-covid-uk-warning-hope/

In places like Thailand, where the majority of vaccines are of the inactivated virus type that are turning out to be much less effective at preventing transmission of the virus, but importantly do appear to be very effective at preventing serious illness or death, herd immunity does not appear to be possible.

Does anyone have any other data that bolsters or refutes this assertion?