The original L and S strains from China were replaced by the G strain from Italy in the spring, probably because it is more contagious and also because China used stringent controls to stamp out the virus.
While previous mutations were minor, the mutations we have seen in recent months are greater and can alter the virus' properties such as mortality or transmissibility. The British variant B. 1.1.7, which was first detected in Kent on September 20th, has 18 mutations that occurred in the same host, possibly a patient who was ill for weeks in which the virus mutated to evade an antibody therapy.
if antibody therapy is administered after many weeks of chronic infection, the virus population may be unusually large and genetically diverse at the time that antibody-mediated selective pressure is applied, creating suitable circumstances for the rapid fixation of multiple virus genetic changes through direct selection and genetic hitchhiking
8 of the 18 mutations in the British variant are in the spike protein, which docks the virus to human cells and which is also targeted by the new mRNA vaccines and by a number of vector vaccines. The B.1.1.7 variant has made the virus more transmissible so that it is now the dominant strain in the UK, from where it has spread to more than 40 other countries. Even if virus mortality is not increased, it will kill many more people because it spreads so rapidly. Despite containment measures, daily new infections in the UK have grown 4.5 times in a single month from around 15k to 68k.
Biontech/Pfizer have said that their vaccine is still effective against the new variant, but they have only conducted a small lab test against one of the mutations.
Mutation in SARS-CoV-2 Variant Does Not Affect Vaccine: Study
While the British variant spreads across the globe, new variants keep on popping up almost on a daily basis. The Danish mink variant doesn't seem to have spread, but there is a lot of concern about the South African variant, which is also more transmissible. It's still not clear if it doesn't evade the vaccines. There are also new variants in Nigeria, Brazil and the US, about which little is known at this point.
The virus has become constantly more transmissible and therefor also kills more people. Even if current variants don't evade vaccines, we don't know if the vaccines will have the same efficacy. With the exponential growth we see across the globe, it's just a matter of time before it evades vaccines or leads to reinfections.
It's a miracle that we got vaccines in less than a year, but the rollout of the vaccines won't be fast enough to halt the current exponential growth. More countries need to apply hard lockdowns to prevent further deaths and the rapid mutations which are bound to evade the vaccines sooner or later.