The Delta coronavirus variant, first identified in India, could spread in the U.S., Anthony Fauci, M.D., said in a White House press briefing this week. But Dr. Fauci, who is the director of the National Institute of Allergy and Infectious Diseases, also explained how getting fully vaccinated can provide significant protection.
It’s normal for viruses, including this coronavirus, to naturally mutate as they spread and replicate. Some of those mutations may affect the way a virus infects people, making that variant of the virus potentially more contagious. The Delta coronavirus variant, previously known as B.1.617.2, was first found in India and contains a few different mutations that seem to make it more transmissible and more likely to cause severe symptoms than other versions of the virus. And, as Dr. Fauci said in the briefing, this variant is now overtaking Alpha, previously known as B.1.1.7 and first identified in the U.K.
“In the U.K., the Delta variant is rapidly emerging as the dominant variant,” Dr. Fauci said, explaining that it accounts for more than 60% of infections there and is “replacing” the variant that was previously dominant. Additionally, Dr. Fauci said that the transmission of this variant is peaking among 12-to-20-year-olds, “mainly that group that we’re concerned about here, about making sure they get vaccinated.”
Right now, the Alpha variant accounts for more than 69% of sequenced COVID-19 cases in the U.S., according to the most recent data from the Centers for Disease Control and Prevention (CDC). About 6% of sequenced cases in the U.S. are caused by the Delta variant right now, Dr. Fauci said, and he wants to make sure it is not able to gain more ground. In the U.K., “they had [Alpha] dominant, and then the [Delta] took over,” he said. “We cannot let that happen in the United States.”
Thankfully, the COVID-19 vaccines appear to still be generally effective against both of these concerning variants—especially when people are fully vaccinated. Dr. Fauci pointed to a recent study published on the preprint server MedRxiv, which found that a single dose of the Pfizer/BioNTech and AstraZeneca vaccines showed significantly reduced effects against the Delta and Alpha variants. But the Pfizer vaccine was about 88% effective against the Delta variant and the AstraZeneca was about 60% effective after both doses.
Although this study hasn’t been peer-reviewed yet, it does generally line up with what other studies have shown. Breakthrough infections, meaning COVID-19 infections in people who’ve been vaccinated, are generally very rare. But those breakthrough infections are more likely to happen with coronavirus variants, particularly Alpha in the U.S., according to a recent CDC study. (This study did not find many Delta-related breakthrough infections likely because the number of infections caused by that variant is still relativeley low in the U.S. But Alpha and Delta have some similarly worrying mutations that may make it easier for both of them to infect people.)
So the best way to prevent the spread of the Delta variant and the emergence of new worrying variants is to get vaccinated—fully vaccinated. Even when fully vaccinated people get COVID-19, they are much less likely to require hospitalization, and increasing research also suggests they are significantly less likely to spread the infection. “Particularly if you’ve had your first dose, make sure you get that second dose,” Dr. Fauci said. “And for those who have been not vaccinated yet, please get vaccinated.”
Editor’s note: This story has been updated to provide more clarity on breakthrough infections.