Its not one or two known strains. 123 strains are known. Back then in July, 123 strains were already present but they didn't pose more threat than existent at that moment. Those existent strains are slightly different to eachother. The 2 news strains are distinct in terms of ability to infect more efficiently and rapidly. (Basically, these 2 new strains are refined versions of initial one). Pfizer vaccine contains 1270 amino acids and only 9 of them are changed in the mutant virus. 99% of the protein is still the same but then 1% difference is enough for extremely rapid spread. Remember, its not just about the vaccine, the new 2 variants have influence on diagnostic PCRs too. So testing has also become trickier. The only hope is emergence of new a combination of mutations that may kill the existing mutations. (123 strains are present so that means much more new strains emerging in coming years, hence more probability of emergence of such combination of mutations occuring in near or distant future. Let's keep the fingers crossed). We can't keep the world closed for another 10 years, Till then, we have to accept and adopt a new 'normal'.
Yes, Herd Immunity (not through vaccine, but via Sars-Cov2 infection) is the only solution. With 2 percent death rate, we're looking at 140 million deaths globally in the longer run.