There is no evidence of any known vaccine causing new or more dangerous variants of COVID-19.

Viruses change as they reproduce in order to keep spreading to more cells. These changes are called “viral mutations.” Mutations create an updated version of the virus, which we call a “variant” (though other similar words include “lineage” and “mutant”). Every time the virus divides and makes a copy of itself, it is likely to make a tiny error (a mutation), and there is a chance that these errors (mutations) can be troublesome.

Variants may have different properties than previous versions of a virus. Those properties may allow the virus to infect more people or may cause more severe illness than the original form of a disease. Many variants of COVID-19 have been documented globally. The vast majority of them are not of concern, but some are, and scientists are continuing to monitor the virus as it changes and spreads around the world.

When an individual is vaccinated, they are less likely to contract and transmit the virus, and therefore less likely to contract and transmit viral variants of COVID-19. The more individuals that are unvaccinated, therefore, the more likely more variants are to emerge because there are more people that the COVID-19 virus can infect. As more variants emerge that are more transmissible and more able to evade vaccines, the more likely it is that variants will spread and make global vaccine campaigns less effective. 

Most variants are not significant, and in some cases can even be harmful to the virus itself. When a virus is widely circulating in a population and causing many infections, the likelihood of the virus mutating increases. Some mutations can be more concerning than others for a range of reasons. More concerning COVID-19 variants may spread easier, contribute to more severe symptoms, or be more resistant to current vaccines.

One variant classification scheme defines three classes of SARS-CoV-2 variants: Variant of Interest, Variant of Concern, and Variant of High Consequence. 

The UK variant (B.1.1.7), the South Africa variant (B.1.351), the Brazil variant (P.1), a U.S.-California variant (B.1.427), and a second U.S.-California variant (B.1.429) are all "Variants of Concern". This means there is evidence that they may spread more easily, contribute to more severe disease, and/or evade current tests or vaccines more easily. No existing variants are currently categorized as variants of high consequence.

Myths have been circulating that COVID-19 vaccines are causing new variants of the virus and that vaccinated people are "more likely" to infect others with "super-strains" of the coronavirus. The idea that viruses would evolve and grow stronger to evade vaccines may seem like common sense, but there is no evidence for these claims. Vaccination is very much part of the solution for reducing COVID-19 transmission in addition to existing public health measures.