The Delta Variant: A New COVID-19 Threat

The highly transmissible delta variant of the coronavirus that causes COVID-19 threatens to undermine the progress that the United States has made to end the pandemic.

Delta is now the dominant variant in the United States and accounts for 51.7 percent of positive COVID-19 samples, according to the latest surveillance data from the Centers for Disease Control and Prevention (CDC).

The prevalence of the delta variant, along with the sluggish vaccination rate, are key factors in a recent 10 percent increase in the number of COVID-19 cases in the United States, said CDC director Rochelle Walensky, MD, MPH, in a July 1 briefing.

Designated B.1.617, delta is the fourth “variant of concern” on a list from the World Health Organization (WHO). WHO director general Tedros Adhanom Ghebreyesus, PhD, said delta had now been identified in 85 countries and called it “the most transmissible of the variants identified so far.”

The first case of infection by the delta variant was identified in India in December 2020 and delta soon became the dominant variant there, eventually leading to a deadly second wave of COVID-19 in the country. The variant is now estimated to account for approximately 95 percent of cases that are sequenced in the United Kingdom.

What Exactly Is a Variant?

When a virus infects a new host — an animal or person — it makes copies of itself with small genetic differences called mutations. “As more people are infected, the range of mutations widens, though the vast majority of them go nowhere and don’t affect anything,” says Gabe Kelen, MD, director of emergency medicine at Johns Hopkins Medicine in Baltimore.

“But every now and then, the mutation can occur in a segment of the virus that makes it either more infectious or more deadly. Then that variant starts to predominate because from a Darwinian point of view, it has an advantage out in the world — it can outcompete other versions of the virus,” says Dr. Kelen.

The more infectious or deadly variants of COVID-19 are on the WHO’s “variants of concern” list. In addition to delta, the others are alpha (the variant that first appeared in the United Kingdom), beta (the South African variant), and gamma (the Brazilian variant).

How Contagious Is Delta?

“Most coronaviruses don’t ‘stick’ to respiratory cells well — they sort of fall off, almost like used Scotch tape,” explains Kelen. The SARS-CoV-2 (the official name of the coronavirus that causes COVID-19) first discovered in Wuhan, China, had a pretty adhesive spike protein that enabled it to attach and enter human cells, and the U.K. variant’s spike protein was even stickier, he says.

“Now this delta version has selected for an even stickier version,” says Kelen.

Data from the U.K. released on June 25 suggests that delta is 35 to 60 percent better at spreading than alpha, which a study published in the journal Science in April 2021 concluded was 43 to 90 percent more infectious than the original virus.

In an environment where no one is vaccinated or wearing masks, it’s estimated that the average person infected with the original viral strain would infect 2.5 people, whereas a person infected with the delta variant would spread it to 3.5 or 4 people, according to Yale Medicine.

Is the Delta Variant More Lethal?

“There isn’t clear evidence that the delta variant is more deadly than the original virus,” says Kelen. If considering the total number of deaths, delta may be more life-threatening than other variants simply because more people might become infected with it, he adds.

Early research on the delta variant suggests it may be linked to more severe infections. A study of 38,805 cases published by Public Health England on June 11 found that after controlling for age, sex, ethnicity, and vaccination status, people infected by the delta variant had a 2.61 greater risk of being hospitalized within 14 days of infection compared with people infected by the alpha variant.

If I’m Vaccinated, Do I Need to Worry About the Delta Variant?

“So far, the vaccines that are here in the United States are effective, even against the delta variant. It doesn’t mean you can’t get infected at all, but hospitalizations and deaths are significantly less likely to happen than if you’re not vaccinated,” says Kelen.

Two doses of the Pfizer vaccine were 88 percent effective at preventing symptomatic delta infection and 96 percent effective at preventing hospitalization, according to a U.K. preprint study posted on medRxiv on May 24, 2021.

Moderna announced in a June 29 release that its vaccine is effective against several variants of concern, including delta.

About 8 percent of people who have been immunized against COVID-19 in the United States received the Johnson & Johnson (J&J) vaccine, according to the CDC. A July 1 press release from the company stated that the vaccine showed promise against the delta variant in a laboratory study. Investigators analyzed the blood of eight patients and found high levels of immune response, even higher than those found against the beta variant, “where high efficacy against severe-critical disease was demonstrated,” according to the statement.

The U.S Surgeon General Vivek Murthy, MD, told CNBC on June 30 that there is reason to be hopeful that people who received the J&J vaccine may be protected from delta because of the 92 percent efficacy of the AstraZeneca shot against the delta variant reported by Public Health England. The J&J vaccine and the AstraZeneca vaccine use a similar platform and could be thought of as “cousins,” said Dr. Murthy.

I’m Partially Vaccinated. How Can I Protect Myself From the Delta Variant?

The best protection against the delta variant is to get the second dose of vaccine as soon as you are scheduled to do so, says Kelen. Until you get your second dose, you should continue to mask and social distance, according to the CDC.

“If you didn’t get your second dose as scheduled, it’s not known for certain how long you can go before you may need to start over, but if you can get it within three or four months of your first dose you probably don’t need to repeat or start all over,” Kelen says.

“There is some preliminary data that seems to indicate that ‘mix and match’ for your second dose can strengthen your overall immune response,” says Kelen, referring to the Oxford Vaccine Group’s Com-Cov vaccine trial. In this case, “mix and match” means getting a different brand of vaccine for your second dose rather than getting two doses of the same brand. Right now, there isn’t an official policy to recommend this, but it may become more common and acceptable soon, Kelen adds.

What Is the Risk of Delta for Unvaccinated People?

People who haven’t been vaccinated against COVID-19 are at the highest risk for becoming infected with delta, according to Yale Medicine.

Dr. Walensky, the CDC director, said in the July 1 press conference that the variant poses the greatest danger to areas in the United States where the vaccination rate is low. An estimated 1,000 counties in the country have vaccination rates of less than 30 percent, she said. As of July 2, 54.9 percent of people age 12 and older are fully vaccinated, according to the CDC.

There continue to be “hot spots” in the United States where the rate of COVID-19 infection in high. “There are health systems that are overwhelmed, mostly in places that are significantly undervaccinated,” says Kelen.

Because children under 12 can’t be vaccinated yet, they are at risk from delta as well. But data from Public Health England indicates that hospitalization of children has risen only slightly since the new variant has taken over.

Are Symptoms of Delta Different than Those of Other Variants?

Scientists don’t have data yet to show whether delta symptoms differ from those caused by other variants. A COVID-19 symptom study in the United Kingdom — where 19 out of 20 new cases of COVID-19 are from the delta variant — does provide some insights.

For fully vaccinated people, the top symptoms of delta infection are headache, runny nose, sneezing, and sore throat. Symptoms that were much more common in the earlier version of the virus have dropped down the list: Loss of smell is 11, fever is 12, and shortness of breath is way down the list at 29.

For unvaccinated people, the top symptoms are headache, sore throat, runny nose, fever, and persistent cough. Loss of smell is 9, and shortness of breath is ranked 30.

The researchers behind the study acknowledge that there could be reasons for these changes in top symptoms that aren’t due to the takeover of the delta variant. For instance, people who are vaccinated but develop COVID-19 anyway tend to develop milder symptoms, as do younger people (who now make up a greater percentage of cases in the United Kingdom compared with earlier in the pandemic).

Why Is the WHO Recommending That Even Vaccinated People Mask and Practice Social Distancing Because of Delta, but the CDC Is Not?

People who are vaccinated no longer need to wear a face covering or practice social distancing, according to the CDC, but the WHO maintains that even vaccinated people should social distance and wear masks in poorly ventilated areas and in locations where social distancing isn’t possible.

Los Angeles County recommends that “everyone, regardless of vaccination status, wear masks indoors in public places as a precautionary measure,” citing a recent uptick in COVID-19 cases in the area.

One reason that the WHO’s recommendations are different than the CDC’s is because the vaccines that have been available in the United States have all shown good efficacy against delta, says Kelen.

“WHO needs to have a world view when making their recommendations,” he explains. “In many areas of the world, very few people are vaccinated and amongst those that are, they may have received a vaccine that isn’t as effective against some variants, including delta.”

Should Vaccinated People in the U.S. Start Masking and Social Distancing Again?

In Kelen’s opinion, vaccinated people in the United States can continue to follow the CDC’s guidance and not wear a mask or social distance. “The vaccines have been shown to be pretty effective against all variants so far, particularly in preventing hospitalizations and deaths,” he says.

“However, if the delta variant or some other variant starts to take off or in if some jurisdiction there seem to be tremendous breakthrough infections among vaccinated people, then the recommendations for fully vaccinated people may have to be revisited,” he says.

What Is the Best Way to Stay Safe From the Delta Variant?

“Because the variants are formed in a person who is infected, the best way to keep variants from being created is for everyone to be fully vaccinated if possible — that’s a huge underscore,” says Kelen. Some people can’t be vaccinated because of certain health issues, he adds.

Decisions that you make regarding vaccination aren’t the same as other personal choices, Kelen says. “Choosing not to get vaccinated can have huge ramifications for people around you — your own family, friends, and society at large. You may think, ‘I don’t want to get vaccinated, I’ll just take my chances and get infected,’ but in this case your decisions may harm people you don’t even have a clue about,” he says.