The coronavirus responsible for the pandemic, SARS-CoV-2, has nearly 30,000 bases, or nucleotides. As the virus evolves and spreads from host to host, some of these bases change. If just 20 bases changed, that would yield more than a trillion possible variants different from the strain responsible for the first outbreak. Of the 136 million confirmed Covid-19 cases in the world to date, one million individuals have had their virus sequenced. And of those one million sequences, scientists have been concerned about only a handful of variants, because they are more infectious, cause more severe illness or partly evade our immune response or all of the above... Critically, the number of mutations does not necessarily correlate with any change in the virus’s infectiousness. For example, a variant in Angola was recently found to have the most mutations to date, but there isn’t any clear evidence that it causes more disease. It takes considerable work — studies in the lab as well as in large numbers of people — to ascertain whether a variant might cause an increase in cases, hospitalizations, fatalities and reinfections. The vaccines being administered in the United States were developed before some variants emerged. But so far, they appear to be effective in fighting those viruses. The Moderna and Pfizer vaccines, which use a technology called mRNA, have been shown in laboratory studies to be effective against each of the major variants. Even when the variants make the vaccines less effective, the mRNA coronavirus vaccines in use right now are so good that a reduction would not likely affect the efficacy rate in a meaningful way.