Since the coronavirus that causes COVID-19 was first detected in the U.S. in early 2020, several new strains of the virus, known as variants, have emerged around the world. Some have made major headlines and upended daily life while others have come and gone with little notice by the general public. By late 2020, a variant known as Delta (B.1.617.2) emerged and had a major impact on the pandemic around the world.
Soon after its discovery in India and arrival in the U.S., Delta quickly became the dominant strain in the country and prompted a series of changes to the guidance from the Centers for Disease Control and Prevention (CDC) to mitigate its spread.
Data suggested that the Delta variant spread more easily, caused more severe illness, and caused more breakthrough infections than other variants at the time. It was classified as a “variant of concern” in June 2021, and by July 2021, it was estimated that the Delta variant accounted for 83 percent of all coronavirus cases in the U.S. and that number continued to rise.
Since then, the Delta variant has been overshadowed by variants like Omicron. In April 2022, the Delta variant was downgraded to a "variant being monitored," meaning that the CDC believed that it no longer posed a significant risk to public health, but it still remains in circulation.
Although the pandemic had appeared to be improving, Delta caused another deadly COVID-19 surge and sparked concern about what future variants might mean for an end to the pandemic. So how dangerous was the Delta variant, and what did it mean for pandemic life? Here's everything parents need to know.
Where Did the Delta Variant Come From?
The Delta variant—also known as B.1.617.2—had multiple mutations that differentiated it from other strains of COVID-19. "It basically evolved into a more transmissible virus," explains Jim Versalovic, M.D., Ph.D., pathologist-in-chief and interim pediatrician-in-chief at Texas Children's Hospital.
Delta was first detected in India in late 2020, where it caused waves of infections and deaths. It then made headlines in the United Kingdom, where it began spreading rapidly and delayed reopening efforts. In early July 2021, it overtook the formerly dominant variant in the U.S. (the B.1.1.7 Alpha variant from the United Kingdom), and areas of the country with low levels of vaccination were hit the hardest.
As of March 2022, there were confirmed cases of Delta in 188 countries, though it was estimated that the variant accounted for less than 1% of COVID-19 cases in the U.S. by that time.
Is the Delta Variant More Dangerous?
When it first emerged, the Delta variant was more infectious than earlier forms of the coronavirus. In fact, studies have shown that it was 40 to 60 percent more transmissible than the B.1.1.7 Alpha variant—and B.1.1.7 itself was 50 percent more contagious than the original SARS-CoV-2 virus from Wuhan. In other words, Delta was around 75 percent more transmissible than the original strain of COVID-19, according to F. Perry Wilson, M.D., a Yale Medicine epidemiologist, in an article from Yale Medicine.
The fact that Delta was more transmissible also made it more dangerous. As Dr. Mike Ryan, the executive director of the World Health Organization (WHO) health emergencies program, explained in a June 2021 news conference, the Delta variant had the potential to be deadlier simply because it was “more efficient in the way it transmits between humans and it will eventually find those vulnerable individuals who will become severely ill, have to be hospitalized and potentially die.”
Ultimately, the data also suggested that the Delta variant itself was, in fact, more dangerous than previous versions of the virus, causing more severe illness in infected people. A Scottish study published in The Lancet in 2021 suggested that Delta was associated with double the hospitalizations compared to the B.1.1.7 Alpha variant (the predominant strain in the U.S. just before Delta).
What Are the Symptoms of the Delta Variant?
Experts have found that the Delta variant had slightly different symptoms than other strains of COVID-19. “It seems to present more often in the upper respiratory tract,” says Steven Abelowitz, M.D. FAAP, a board-certified pediatrician who serves as the medical director and president of Coastal Kids pediatric medical group. Patients often experienced runny nose, fever, headache, and sore throat. Other side effects commonly associated with the coronavirus—like coughing or loss of smell—seemed to be less common with Delta.
Though the Delta variant caused more severe illness in some, like previous strains, it still caused only mild symptoms in others. In those cases, the disease was more likely to be mistaken for the flu, seasonal allergies, or even a cold, which increased the likelihood of spread. The concern over this potential misdiagnosis and the highly transmissible nature of Delta—as well as the wide availability of COVID-19 tests—can be seen in the CDC’s quarantine and isolation guidelines, which now call for testing under more circumstances than early in the pandemic.
Does the COVID-19 Vaccine Protect Against the Delta Variant?
Research shows that the available COVID-19 vaccines have been less effective against infection and symptomatic disease with Delta than with the original virus and previous variants. The Delta variant caused more breakthrough cases (or COVID-19 cases in people who are fully vaccinated) than previous variants. But that doesn’t mean that they offered no protection from Delta.
A study conducted by the CDC during the summer of 2021, when the Delta variant fueled a surge in COVID-19 cases, found that people who were not fully vaccinated had about 10 times the risk of being hospitalized with or dying from COVID-19 compared to people who were fully vaccinated.
These results suggested that despite the higher rate of breakthrough infections with Delta, the vaccines were still effective against serious illness and death. The CDC estimates the two doses of either the Pfizer-BioNTech and Moderna vaccines lowered a person’s risk of COVID-19-related hospitalization by 85% during the Delta variant period in 2021.
Still, infection was and is possible even in fully vaccinated people. And evidence suggests that vaccinated people are able to spread the Delta variant to others—partly because people infected with Delta carry a higher viral load than previous variants. One Chinese study suggests that viral loads were about 1000 times higher with Delta than other variants.
This data was part of the reason why the CDC switched gears during the Delta surge to recommend that everyone begin wearing masks in areas of high transmission, after previously stating that most fully vaccinated people could safely discontinue mask-wearing.
Evidence of waning vaccine protection over time and the emergence of more serious and highly transmissible variants like Delta were among the reasons that the Federal Drug Administration (FDA) authorized COVID-19 vaccine boosters. By November 2021, all adults 18 or older were eligible for a booster shot. In December 2021, eligibility was extended to 16- and 17-year-olds, and by May 2022 everyone ages 5 and older could receive a booster dose.
How to Protect Your Family
Experts stress that vaccination is important for preventing severe disease, hospitalization, and death from COVID-19. The emergence of variants like Delta only emphasizes the importance of vaccination.
Mutations and the variants they create are expected and will continue to emerge, but according to the CDC, widespread vaccination can help reduce the spread of the virus, and "the less a virus spreads, the less opportunity there is for new variants to emerge."
In the U.S., people ages 5 and older are all eligible for a COVID-19 vaccine and booster. Clinical trials for children 6 months to 4 years old are underway, and the FDA expects to meet to review the study data in June 2022. In the meantime, the FDA and the CDC encourage every eligible person to receive a vaccine.
In addition to getting vaccinated and staying up to date on your vaccines, it’s still important to follow other precautions such as following the CDC’s recommendations for hand-washing, face masks, and quaratine and isolation, when appropriate.
