Viruses, including the novel coronavirus, are constantly changing. Over time this can lead to the emergence of variants with characteristics different from those of the original one. Sometimes the variants disappear, but other times they stick around and become more transmissible or deadly than the original virus.

In the case of COVID-19, several variants have been detected around the world, including one originating in the United Kingdom named B.1.1.7. It has since appeared in the United States, and earlier this year health officials reported that it may be associated with a higher risk of death than the original virus. More studies are needed to confirm this finding, according to the US Centers for Disease Control and Prevention (CDC). Another variant, B.1.351, was found in South Africa last October and in this country in January. A third variant, P.1, was identified in Brazil in early January and in the United States at the end of January.

Just recently, scientists identified two homegrown variants. One discovered in California is B.1.427/B.1.429, which may be more easily transmitted and deadlier than the original strain—and may be responsible for the dramatic rise in COVID-19 cases and related deaths in the state. The other appeared in New York City and is called B.1.526.

Researchers try to understand and anticipate variants by studying lab samples of the virus and looking for changes in its genetic makeup, especially in the spike protein—a key part of the SARS-CoV-2 virus that attaches to human receptors in the nose and throat, causing COVID-19. (When the virus evolves, it may lead to mutations that could increase the amount of virus transmitted or the affinity of the virus to receptors and make it more infectious.) Identifying these changes is important because the currently authorized vaccines train the immune system to recognize the spike protein and enhance the immune response to it.

If variants cause changes to the spike protein, vaccines developed without those potential changes in mind could become less effective; antibodies created in response to the vaccine might not recognize the altered virus when the variant enters human cells. That has been the case in South Africa, where a vaccine made by AstraZeneca (available in some countries but not the U.S.) is seemingly not as effective against the variant.

Since mutations to the virus could change the vaccines' effectiveness, the CDC and companies making the vaccines monitor and test for variants and can tweak the vaccines to protect against the variants if necessary.

Given the highly transmissible new variants, it is key to continue to follow all measures to prevent infection.

Get vaccinated when you can. If 70 to 90 percent of people in the United States are vaccinated, we could achieve “herd immunity”—meaning enough people are immune to COVID-19, through either vaccination or having had the disease, that transmission of the virus is less likely. If you're getting a two-dose vaccine, be sure to keep your appointment for the second one.

Cover your face. Since vaccinated people may still be able to transmit the virus, it's crucial that everyone continues to wear masks. And while health officials believe the current vaccines may protect against the virus and its variants, there is still a risk of infection from a variant. Make sure your mask has two or more layers; covers your chin, mouth, and nose; and fits snugly against your face. The CDC recently issued new guidance on wearing two masks for extra protection.

Maintain social distancing. This is especially important if you haven't been vaccinated. Stay at least six feet from anyone not in your household or “pod” and avoid crowds when you're out.

Wash your hands often. Continue to soap up your hands for at least 20 seconds after being outside and apply hand sanitizer often while you're out, especially if you've touched any surfaces in a store, restroom, or other public area.

Sign up for alerts regarding vaccines. Talk to your doctor or sign up with your city's or county's department of health to receive notices if companies make changes to the vaccines or create booster shots.

Dr. Clifford is the Melba and Forest Seay Professor of Clinical Neuropharmacology in Neurology at Washington University School of Medicine in St. Louis.