The SARS-CoV-2 coronavirus seems to be suddenly acquiring mutations at a rapid rate. The most worrying variants, first discovered in South Africa and Brazil, increase the virus’s contagiousness and may even help it evade the human immune system. These characteristics are helping the new variants outcompete the original virus, allowing them to spread quickly around the world.

Viruses, including SARS-CoV-2, are constantly evolving and acquiring mutations that don’t affect the virus much. The reason public health experts are concerned is that the new mutations improve the virus’s spike protein, which helps the pathogen enter cells and is the target of most vaccines. If the spike protein evolves sufficiently, the virus may eventually be able to reinfect individuals who have already had COVID-19 or been vaccinated against it.

But scientists say it will likely be years before the vaccine stops working entirely—if it ever does. In the meantime, social distancing remains the best way to fight the new mutants. After all, the more viruses that exist in the world, the greater the chance that one will evolve a dangerous mutation.

In this video, we explain what the new variants actually are, how they arise and spread, and what they could mean for the future of our ability to vaccinate ourselves against the virus.