According to the CDC, the current crop of vaccines are 91% effective against the original version of the SARS-CoV-2 virus, and are 66% effective against the Delta variant. That said, 66% is better than nothing, and the vaccines do appear to lessen the intensity of illnesses associated with the disease.(1)
The good news is that the companies manufacturing the vaccines are working on booster shots tailored to the Delta variant. Between reports that the effectiveness of vaccinations fades with time and reports that booster shots can dramatically improve the level of antibodies to the virus, this makes the case for booster shots relatively ironclad.
Of course, the massive number of unvaccinated are the breeding ground for new variants. So we are far from done. Keep masking.