ChatGPT's New Skills Resident Evil 4 Remake Galaxy A54 5G Hands-On TikTok CEO Testifies Huawei's New Folding Phone How to Use Google's AI Chatbot Airlines and Family Seating Weigh Yourself Accurately
Want CNET to notify you of price drops and the latest stories?
No, thank you

Coronavirus delta variant: What you should know

COVID-19 variants are inevitable, but most of us didn't see delta coming. Here's what you should know, and when you should get tested.

The CDC now considers delta a "variant of concern."
Andriy Onufriyenko/Getty Images
For the most up-to-date news and information about the coronavirus pandemic, visit the WHO and CDC websites.

The coronavirus is, unfortunately for us, good at doing what viruses do best: mutating in order to become more efficient and infect more people. The delta variant, first documented in India, continues to spread rapidly across the globe and is surging in the US, setting the country back during a summer that was supposed to offer some protection. 

In July, the Centers for Disease Control and Prevention recommended fully vaccinated people start wearing masks indoors again if they live in an area of "substantial or high" COVID-19 transmission, citing how contagious the delta variant is and the way it "behaves differently" from variants of the past. In August, public health officials announced all Americans will need a booster shot, due in part to the highly contagious delta variant. As schools begin to open up this fall, exposing millions of children too young to get a coronavirus vaccine, experts wonder how, and when, the delta variant outbreak will ease up

Now playing: Watch this: COVID-19 boosters and the delta variant: What you need...

The variant is about 60% more transmissible than the alpha variant first documented in the UK, British epidemiologist Neil Ferguson told reporters in June, and it's suspected to carry the potential for more severe disease. In a Scottish study published on June 14, researchers found that the delta variant carried double the risk of hospitalization compared with the alpha variant.

All three vaccines available in the US are said to have excellent efficacy against severe disease caused by COVID-19. But how do they fare against the more contagious variant? Research available shows that vaccination is an especially essential tool against a variant as contagious as delta. As researchers continue to learn more, here's what we know right now. 

Breakthrough COVID-19: Vaccinated vs. unvaccinated

Breakthrough infections, or cases of COVID-19 in people who've already been vaccinated against it, are more common with the delta variant. A CDC report in August showed data from a COVID-19 outbreak in Massachusetts in which three-quarters of people infected were fully vaccinated, and 90% of tested cases in that outbreak were caused by the delta variant. What's more, the same report suggests that fully vaccinated people who do get a breakthrough case might be just as likely as an unvaccinated person to spread it to someone else. 

But fully vaccinated people are still much less likely to get severely sick with COVID-19 than unvaccinated people, according to the CDC. In a study that looked at health records from May until the end of July, when the delta variant was dominant, unvaccinated people were about five times more likely to get infected with COVID-19 than fully vaccinated people, and 29 times more likely to get hospitalized with COVID-19 than people who were vaccinated, the CDC reported. 

Breakthrough infections might also be much less likely to lead to long COVID, a condition where a person experiences lingering symptoms after clearing the coronavirus from their body. According to a New York Times report on a study from The Lancet, the odds of having long-term symptoms of COVID-19 was 49% lower in people who experienced a breakthrough infection than unvaccinated people who got infected. 

Delta's side effects 

In mild cases, the delta variant may show up a little differently, and that might be fooling a lot of people who think they just have a cold. Tim Spector, a British epidemiologist and co-founder of the ZOE COVID Symptom study in the UK, says that since May, the top symptoms of COVID-19 being recorded in the app have changed. He says the No. 1 symptom of COVID-19 is now headache, followed by sore throat, runny nose and fever -- not the more "classic" COVID-19 symptoms. Coughing is now the fifth-reported symptom.

"We don't even see loss of smell coming into the top 10 anymore," he says. "This variant seems to be working slightly differently." 

Spector says these changes -- which appear to be linked to the delta variant -- may cause people to continue going out, thinking they have a common cold instead of COVID-19.

Other anecdotal reports from physicians and people who've had COVID-19 this summer, versus last winter or earlier, suggest the delta variant is presenting a little differently -- especially in fully vaccinated people who are much more likely to have a mild case of COVID-19 that resembles a cold. A doctor from Florida told NBC that the reason more people are reporting earaches as a symptom of COVID-19 from delta is the fact that sore throats are now so common, and sore throats can cause earache.

Because of how much COVID-19 is circulating in communities right now, it's best to get tested even if you are fully vaccinated and feel just a little sick, according to CNN medical analyst Dr. Leana Wen. 

"Given how much coronavirus is surging in most parts of the country, keep your radar on high alert," Wen said. "If something doesn't feel quite right to you, get tested."


The WHO labels "variants of concern" and "variants of interest" using letters of the Greek alphabet. The term means they have been associated with an increase of transmissibility, increase in virulence or change in clinical presentation, a decrease in effectiveness of public health measures or some combination of the above, according to the WHO

Eugene Mymrin/Getty Images

Boosters for delta? 

Pfizer announced that the company is working on a booster specifically for the delta variant, citing real-world data from Israel that shows that Pfizer's two-dose regimen is less effective against infection from delta compared with previous variants -- down to 64%, though the same data found that the vaccine is still 93% effective at preventing severe disease. 

Although we won't be receiving a delta-tailored vaccine right away, White House COVID-19 Response Team officials announced in August that US adults who received Moderna or Pfizer COVID-19 vaccines will need a booster shot eight months after their second dose. When they made their recommendation, they looked to the information from Israel -- a highly vaccinated country that is seeing a surge from delta. Although health officials attest that the vaccines remain effective against severe disease and death, a third dose is needed to "stay ahead" of the virus.

At the briefing the announcement was made, Dr. Anthony Fauci, chief medical advisor to President Joe Biden, said that "higher levels of antibody may be required to protect against the problematic delta variant." This antibody response, though not the full picture of immunity following vaccination, is easiest to measure and can be achieved by a third dose of mRNA vaccine. 

People who got the one-dose Johnson & Johnson vaccine aren't included in the booster recommendation right now, either for an extra dose of Johnson & Johnson or an mRNA vaccine, but officials are evaluating data that suggests an extra shot of Johnson & Johnson boosts immune response against COVID-19. Although questions about the Johnson & Johnson vaccine's efficacy have been fueled by the delta variant (a small study found Johnson & Johnson doesn't protect against delta like it does other variants), a study on health care workers in South Africa where the delta variant was circulating found that the one-shot vaccine was protective against severe disease. 

For information on how and when to seek an extra shot, check out this COVID-19 booster shot explainer

Moving forward

The expert advice does not seem to change as the coronavirus does -- getting vaccinated and gaining immunity against COVID-19 is the surest way to prevent severe disease caused by any variant. When fewer people get infected with COVID-19, the coronavirus has fewer hosts within which it can mutate and produce new variants.

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.