Delta Variant: What to Know

Just when COVID-19 rates and hospitalizations in the U.S. seemed to be declining, the Delta variant forced a strong surge in the wrong direction. The “rapid and alarming” rise in cases and hospitalizations started between late June and early July, according to the Centers for Disease Control and Prevention.

Delta is now the predominant COVID-19 variant — by far — accounting for more than 99% of U.S. cases. And it’s no longer a given that you can largely escape COVID-19 infection while outdoors. Experts below describe why Delta is so powerful and emphasize that being fully vaccinated is critical.

[See: What Are the Symptoms of Coronavirus?]

Delta Cases Are Dominant

“Delta is just so much more transmissible,” says Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organization, a research institute within the University of Saskatchewan in Canada. “Every community that it’s gotten into has seen these strong increases in COVID cases, including some in vaccinated people. So, it’s definitely something we really need to be very concerned about, particularly in places that don’t have robust health infrastructure.”

Virus variants, in themselves, aren’t necessarily alarming, Rasmussen explains. “Variants have been emerging throughout the course of the pandemic,” she says. Most worrisome “are those that have properties that make them more effective pathogens,” or organisms that can cause disease.

Delta-related cases may be more severe than with previously circulating variants. “Certainly, that’s what the epidemiological data suggests,” Rasmussen says. “People who contract Delta have a higher risk of hospitalization, a higher risk of severe outcome and a higher risk of death. So that certainly suggests it is more pathogenic.”

However, Delta’s increased impact relative to other COVID-19 variants may be largely due to its predominant proportion and ability to spread, Rasmussen adds. Although Delta appears to increase your risk of infection, she says, what hasn’t been determined is whether the variant inherently causes worse disease, or if with more people being infected, more are therefore likely to be hospitalized.

Why Is the Delta Variant Highly Contagious?

Why Delta spreads more easily is better understood, Rasmussen says: “We do know that people who are infected with Delta have much higher levels of viral RNA in their upper respiratory tract, which means they’re probably shedding a lot more infectious virus than with older variants.”

With viruses, the “receptor-binding domain” is the key part that allows it to launch its invasion. “It’s where the virus attaches to our human cells, enters into our cells and into our body and starts the process of making us sick,” explains Dr. Kathleen Neuzil, a professor in vaccinology and director of the Center for Vaccine Development and Global Health at the University of Maryland School of Medicine.

Unfortunately, Neuzil says, “This Delta variant has mutations and changes in that receptor-binding domain that make it easier to attach to our cells and easier to infect — so even less (amount of) virus can make people sick. That has been really challenging — that this particular strain is more infectious right at the time when we’re taking masks off, we’re going back to school and we’re decreasing social distancing.”

What to Know About the Delta Variant

Delta has a wide scope and some standout features. However, health consequences and preventive measures largely align with what’s already happened with COVID-19 throughout the pandemic. Here are some details on Delta:

— Twice as contagious as earlier variants, Delta spreads more rapidly and causes more infections in the population.

— Delta may cause more severe illness than previous virus versions in unvaccinated people.

— Fully vaccinated people with Delta can spread it to others — although the transmission window appears shorter than for unvaccinated people infected with Delta.

— Unvaccinated people are at higher risk for infection, as with the original virus version and other variants.

COVID-19 symptoms may be slightly different than for the original version, with fever, headache, sore throat and runny nose more common, but cough and loss of smell and taste less prevalent.

Vaccines are effective against Delta, particularly for people who are fully vaccinated.

— Southeastern states — such as Louisiana, Florida and Mississippi — are experiencing the highest proportions of residents who have tested positive for COVID-19 in the Delta surge.

— The Delta variant has been detected in 150 countries or more worldwide and is prevalent in most of them.

Children who are too young to be vaccinated are at higher risk of contracting Delta.

Outdoor settings no longer represent COVID-19 low-risk zones. “Through the earliest days of the pandemic to as recently as this past spring, we emphasized that in general, the outdoor air was a much safer place to be, because the virus dissipated so quickly for the amount of virus in somebody who was breathing out,” says Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota.

That dynamic has changed. “Since Delta has turned up, we now have a whole series of outbreaks that have occurred literally outdoors — by outdoor exposure only,” Osterholm says. “In fact, in Minnesota we now have over 50 outbreaks, many of them just (arising) in the last several months, associated entirely with outdoor air exposures. That tells you something about the infectiousness of the virus. Because if you can transmit the virus in outdoor air and contact like that, imagine what it’s like indoors.”

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High-Risk Populations for COVID

As with the “original” COVID-19 virus and other variants, higher-risk groups — older adults, people who are immunocompromised and those with comorbidities such as diabetes and asthma — are essentially the same, Rasmussen says.

Children are still at much lower risk for COVID-19 disease overall, Rasmussen says. However, younger kids, because they’re unvaccinated, now make up a larger proportion of cases than before, when vaccines weren’t available.

“With the Delta variant in (recent) weeks, we continue to see a rise in COVID-19 cases in children,” says Dr. Diego Hijano, a pediatric infectious disease specialist at St. Jude Children’s Research Hospital in Memphis, Tennessee. “And that rise has led to more hospitalizations, more severe disease, more side effects.”

COVID Variants of Concern

Some COVID-19 variants pose a greater threat than others. According to the World Health Organization, variants of concern fit at least one of the following criteria:

— Increase in ability to spread or detrimental change in how COVID-19 is affecting populations and communities.

— Increase in virulence (severity) or changes in clinical disease.

— Decreased effectiveness of public health and social measures (like masks or crowd restrictions), or available diagnostic tests, vaccines or therapies.

These are current COVID-19 variants of concern as designated by the WHO (in Greek alphabetical order):

Alpha. Originated in the U.K. in September 2020.

Beta. Originated in South Africa in May 2020.

Gamma. Originated in Brazil in November 2020.

Delta. Originated in India in October 2020.

COVID Variants to Watch

Variants of interest have genetic changes with actual or predicted effects on virus characteristics including transmissibility and disease severity. In addition, these variants are identified to cause significant community transmission or multiple COVID-19 clusters in multiple countries, with increasing prevalence.

The Mu variant, which originated in Colombia in January 2021, is among current COVID-19 variants of interest, according to the WHO. However, Mu is not classified by the CDC as such for the U.S., where it peaked in late June 2021 and has been fading since.

“We want to keep these other variants in mind,” Osterholm says. “We want to keep watching them carefully. But it seems as if transmissibility, or infectiousness, probably trumps all other aspects of the virus. It would take a tremendously infectious virus to knock Delta off the block.”

COVID-19 Vaccine Effectiveness for the Delta Variant

Being fully vaccinated is key to fending off Delta-fueled COVID-19, even though breakthrough infections can happen (as with any vaccine).

“The goal of vaccination is really to protect against the disease,” Rasmussen says. “It’s a bonus if it protects against infection. It seems as if protection against infection has decreased a little bit with Delta, even after two shots. But it does look like protection is still fairly robust. Even in people who do have breakthrough infections, they’re largely not serious.”

Vaccination continues to make a major difference. “Vaccine effectiveness continues to be high, protecting against the severe outcomes,” Rasmussen says. “Which, to me suggests: Even if the virus can get past that first line of defense, those neutralizing antibodies, people who are vaccinated are mounting rapid, protective immune responses. And that’s clearing the virus out very quickly.”

Encouraging results on vaccine effectiveness during the Delta-prominent period of COVID-19 appear in the Sept. 17 issue of the CDC’s Morbidity and Mortality Weekly Report. For all three U.S. vaccines, effectiveness remained high (86%) against hospitalizations. Moderna had the highest effectiveness (93%), followed by Pfizer (88%) and Johnson & Johnson (71%) for fully vaccinated participants.

Booster Vaccines and Delta Variant

Booster vaccines may provide some extra protection against Delta, but COVID-19 boosters are not currently recommended in the U.S. other than what are instead referred to as third doses for people at higher risk because they have weakened immune systems.

On Friday, Sept. 17, the Vaccines and Related Biological Products Advisory Committee of the Food and Drug Administration rejected the Biden administration’s plan to offer extra doses to the general U.S. public, arguing that completing the initial two-dose series provides sufficient protection against COVID-19. However, VRBPAC agreed that immunocompromised people, plus older adults ages 65 and up, could benefit from a third dose.

An additional dose may yet become widely available. “As we see more waning of immunity over time, we shouldn’t be surprised that we need a third dose,” Osterholm says. “We know that you get a much larger boost out of a third dose than the first or second one. And we have many (other) vaccines that have multiple doses for what we call a primary series.” For instance, he says, the hepatitis A vaccine requires three doses, with the final dose given a year later.

[SEE: What to Say to Friends or Family Members Who Hesitate to Wear a Mask.]

Stopping the Spread of the Delta Variant

To counter Delta’s spread, “We should be doing the best we can,” Neuzil says. “The more you’re around children, the more you’re around immunosuppressed people — the more you need to mask, the more you need to be careful, the more you need to social distance.”

Throughout the pandemic, hospitals haven’t let up or loosened their restrictions, and staff members never stopped wearing masks, Neuzil notes. But with Delta making its mark, she says, now it’s back to wearing N95 masks, not eating together as a group and other protective measures.

For public health, “We’re not putting society on total lockdown,” Neuzil says. “We’re letting stores and coffee shops stay open, but we are asking people to get vaccinated and wear masks .”

The advent of Delta highlights the need for continuing protective measures against COVID-19. Public health prevention includes:

— Vaccination for everyone who is eligible.

— Protection with medical-type masks.

Social distancing, including outdoors.

Bottom line is: “Just don’t get exposed,” Osterholm says. “Still avoid crowds. Mask using an N95 mask, which is much more effective. And make sure that all the people around you are vaccinated. If you’re a parent and your kids can’t be vaccinated because of their age, please get vaccinated for your kids, if nothing else.”

Vaccination helps everyone, Rasmussen agrees. “We need to think of getting as many people vaccinated as possible,” she says. “Because that is how we will reach the herd immunity threshold and prevalence will decrease significantly — including with Delta — if as many people are vaccinated as we possibly can get.”

Herd immunity doesn’t happen overnight, Rasmussen notes. “It doesn’t mean that the vaccines aren’t working — it just means that not enough people are vaccinated yet to control the spread,” she says. “So, the take-home message here is: It’s never too late. If you’re not vaccinated, get vaccinated. That’s how we’re going to end this thing.”

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