I think that it is not helpful for people's general understanding when the news media are often IMO confusing the issue by using incorrect nomenclature, and misrepresenting scientific studies.
As I understand it, vaccines are often given in a series, in order to adequately protect an individual.
The initial dose "primes" the immune system to recognize the foreign antigen. The second, or subsequent dose of the vaccine, is a "booster" and is administered to reinforce the effects of the first dose, and provide more stimulation to the immune system.
How Vaccines Work: A Step-By-Step Guide | St. Luke's Health
When a virus mutates enough, so that the immune system does not adequately recognize and respond to the newly mutated variant, then a NEW or tweaked vaccine is needed, for example as happens almost every year with the influenza vaccine. This is not a booster, per se, but a new vaccine. JMO
From what I have read so far, the Pfizer vaccine is still providing good efficacy (80%+) against the Delta variant infection (screenshot from)
DEFINE_ME
However it is my understanding that the Astra Zeneca vaccine is still effective against Delta infection, but somewhere in the 60-70% range.
AstraZeneca’s Covid-19 vaccine shows effectiveness against Delta variant
BOTH Pfizer and AZ seem to be effective against HOSPITALIZATION from the Delta variant:
AstraZeneca, Pfizer vaccines effective against Delta COVID-19 variants-study
All JMO until I can find links.
Also, the UK relied heavily on the AZ vaccine, and extended the vaccine interval between first and second doses. I think that this strategy actually wasn't a bad idea (I'm still not sure!), but maybe people relaxed too much, before they were fully vaccinated?
Also, it seems that the UK were not as strict as they could have been with regard to international travel.
In addition, I think that there has been a lot more testing over in the UK (compared to where I am in the US), but there seems to be great reliance on "lateral flow tests" which depending on the manufacturer, may not be as reliable as a lab based PCR test.
How reliable are lateral flow COVID-19 tests? - The Pharmaceutical Journal
How likely is a positive COVID-19 lateral flow test to be wrong?
It's my understanding that if one is testing every day using a less reliable test however, it is more likely to pick up a positive test, than say just doing a random once weekly test?
Vaccine efficacy, effectiveness and protection
These CV19 vaccine efficacy levels are still favorable when compared to annual influenza vaccines, although obviously, more effective is better.
Apparently, there are plans to "tweak" vaccines to provide improved efficacy against emerging variants, and/or possibly provide boosters for those, such as seniors who may mount a less robust immune response to the initial 1-2 doses.
ETA Links:
How Vaccines Work | PublicHealth.org
Booster Shots
Efficacy and effectiveness