When viruses spread, they also change—a process called mutation. These changes can be either helpful or harmful in helping the virus do what it does best: multiply and infect people.

Think about these mutations like a game of broken telephone; the exact words change slightly every time they transfer to another person. The key messages will still be there, but some details are likely to change.

While most mutations have no real impact on the virus, some can be significant enough to cause a change in how the virus spreads, or how severe infections might be in people. Some mutations can also make viruses less contagious and severe, but these small changes are a natural part of the virus' evolution. So, how does a vaccine respond to these mutations if they are always changing?

Vaccines activate a bunch of different cells and types of antibodies to fight infections. Most of the vaccines that have been given emergency COVID-19 authorizations work by activating a variety of antibodies that focus on different parts of the COVID-19 virus, instead of just one specific characteristic.

This approach means that vaccines will likely have some effectiveness against the virus, even with its inevitable mutations. But as more time passes, and as COVID-19 continues to spread, some mutations will likely make the virus look very different than its original form. This would help the virus potentially evade the protection of existing vaccines.

This is why it is so important to vaccinate as many people on the planet as quickly as possible. Scientists can adjust vaccine formulas to target newer parts of these mutations. That can offer more protection against mutations. However, those adjustments take time and more clinical trials.

As viruses change over time to create new mutations, "variants" can emerge. Variants are viruses with one or more new mutations. Vaccines do not cause new variants because vaccines are not viruses, which constantly evolve. Currently, vaccines target the early versions of the COVID-19 virus, and that poses challenges when variants start to spread. For this reason, variants that don't respond to current vaccines will be more likely to spread than the original forms of SARS-CoV-2. Drugmakers are working to address this potential problem now, by evaluating how to tailor vaccines to address variant mutations.

An open letter by Belgian veterinarian Geert Vanden Bossche discusses his fears about COVID-19 vaccination causing the spread of "out of control" variants. This letter has gone viral, particularly among anti-vaccination activists, who are asking that people not allow themselves or their families to get vaccinated. Though the letter has been disproven, these claims continue to circulate.