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5 Things To Know About the Delta Variant: The Predominant COVID-19 Strain Has Put The Focus Back On Prevention

By Kathy Katella - Yale Medicine

August 19, 2021

Even as people began to feel some hope - or at least, have some cautious optimism, early this summer, that the Pandemic, could recede to the background, there was still the threat that new mutations, of the COVID-19 Virus, could bring it back and it might be, even stronger.

A major worry right now is Delta, a highly contagious SARS-CoV-2 Virus Strain, which, was first identified in India, in December. It swept rapidly through that country and Great Britain, before, reaching the U.S., where it is now, The Predominant Variant.

The Centers For Disease Control And Prevention (CDC), described The Delta Variant, as more transmissible, than the Common Cold, Influenza, as well as the Viruses that cause: Smallpox, MERS, SARS, Ebola and even called it, as contagious as Chickenpox, in an internal document, a copy of which, was obtained by and reported on, in The New York Times. The highest spread of Cases and severe outcomes, is happening in places with Low Vaccination Rates, virtually all hospitalizations and deaths, have been among the Unvaccinated, The CDC says. But, The CDC released data in July, that showed, Vaccinated People, can also transmit The Delta Variant, which officials, did not believe to be the case with other Variants, which led the agency to make a prompt revision, to its masking guidelines.

Inci Yildirim, M.D., Ph.D., a Yale Medicine Pediatric Infectious Disease Specialist and a Vaccinologist, isn’t surprised by what’s happening. “All viruses evolve over time and undergo changes, as they spread and replicate,” she says.

From what we know so far, people who are fully Vaccinated against the COVID-19, continue to have strong protection against COVID-19, compared to those, who aren’t. But anyone who is Unvaccinated and not practicing preventive strategies, is at high risk for infection, by the new Variant, doctors say.

Here are five things you need to know about the Delta Variant.

1. The Delta Variant, Is More Contagious Than, The Other Virus Strains Are:

One thing that is unique about The Delta Variant, is how quickly, it is spreading, says F. Perry Wilson, M.D., a Yale Medicine Epidemiologist. Around the world, he says, “Delta, will certainly accelerate the Pandemic.” The first Delta Variant Case, was identified in December 2020, The Delta Variant, soon became the Predominant Strain of the Virus, in both India and Great Britain. By the end of July, The Delta Variant, was the cause, of more than 80% of new U.S. COVID-19 Cases, according to The CDC's estimates.

The July 2021 CDC report, on The Delta Variant's transmissibility, came after an outbreak that occurred in Provincetown, Massachusetts, after a crowded July 4th Weekend, which, quickly turned into a cluster of at least 470 Cases. While the number of reported Breakthrough Cases in general, has been very low in the U.S., three quarters of those infected in Provincetown, were people who had been immunized. According to The CDC, even people with “Breakthrough Cases,” carry tremendous amounts of Virus in their nose and throat, according to preliminary reports, it can spread the Virus to others, whether they have symptoms or not.

The CDC has labeled Delta as, “A Variant Of Concern,” using a designation, also given to The Alpha Strain, that had first appeared, in Great Britain, The Beta Strain, first surfaced in South Africa and The Gamma Strain, was identified in Brazil. (The new naming conventions for the Variants, were established by the WHO as an alternative, to numerical names.

“It’s actually quite dramatic, how the growth rate will change,” says Dr. Wilson, commenting on The Delta Variant's spread in the U.S., in June. The Delta Variant, was spreading 50% faster than Alpha, which was 50% more contagious, than the Original Strain of SARS-CoV-2, he says. “In a completely unmitigated environment, where no one is Vaccinated or wearing masks, it’s estimated, that the average person, infected with the original COVID-19 Strain, will infect 2.5 other people,” Dr. Wilson says. “In the same environment, The Delta Variant, would spread from one person to maybe, 3.5 or 4, other people.”

“Because of the math, it grows exponentially and more quickly,” he says. “So, what seems like a fairly modest rate of infectivity, can cause a Virus, to dominate very quickly.”

2. Unvaccinated People Are At Risk:

People who have not been fully Vaccinated against COVID-19 are the most, at risk.

In the U.S., there is a disproportionate number of Unvaccinated people in Southern and Appalachian states including Alabama, Arkansas, Georgia, Mississippi, Missouri and West Virginia, where Vaccination rates are low. (In some of these states, the number of Cases is on the rise and even as, some other states are lifting restrictions, because, their cases are going down).

Kids and young people, are a concern as well. “A recent study from the United Kingdom, showed that children and adults under 50, were 2.5 times more likely, to become infected with The Delta Variant,” says Dr. Yildirim and so far, no Vaccine has been approved, for children 5 to 12 in the U.S., although the U.S. and a number of other countries, have either authorized Vaccines for adolescents and young children, or are, considering them.

“As older age groups get Vaccinated, those who are younger and Unvaccinated, will be at a higher risk of getting COVID-19 with any Variant,” says Dr. Yildirim. “But The Delta Variant, seems to be impacting younger age groups, more than Previous Variants did.”

3. The Delta Variant, could lead to 'Hyperlocal Outbreaks':

If The Delta Variant, continues to move fast enough, to accelerate the Pandemic, Dr. Wilson, says that the biggest questions will be, about the heightened transmissibility, on how many people will get The Delta Variant and then, how fast, will it spread?

The answers could depend, in part, on where you live and how many people, in your location, are vaccinated, he says. “I call it ‘Patchwork Vaccination,’ where you have these pockets, that are highly Vaccinated, that are adjacent to places, that only have, a 20% Vaccination,” Dr. Wilson says. “The problem is, that this allows the virus to hop, skip and jump, from one poorly Vaccinated area, to another one.”

In some cases, a Low-Vaccination Town, that is surrounded by High Vaccination Areas, could end up with the Virus, contained within its borders and the result could be, “Hyperlocal Outbreaks,” he says. “Then, the Pandemic, could look different, than what we’ve seen before, where, there are real hotspots, around the country.”

Some experts say the U.S., is in a good position, because of its relatively, High Vaccination Rates—or that conquering The Delta Variant, will take a race between Vaccination Rates and The Variant. But if The Delta Variant keeps moving fast, multiplying infections in the U.S., could steepen, an upward COVID-19 Curve, Dr. Wilson says.

So, instead of a three or four year Pandemic, that peters out, once enough people are Vaccinated or are Naturally Immune, (because they have had the Virus), an uptick in Cases, would be compressed into a shorter period of time. “That sounds almost like a good thing,” Dr. Wilson says. “It’s not.” If too many people are infected at once in a particular area, the local health care system will become overwhelmed and more people, will die, he says. While that might be less likely to happen in the U.S., it will be the case in other parts of the world, he adds. “That’s something, we have to worry about, a lot.”

4. There Is Still More To Learn About The Delta Variant:

One important question is, whether or not, The Delta Variant's Strain, will make you sicker, than the Original Virus would. But many scientists say, they don’t know yet. Early information about the severity of The Delta Variant's Study, included a Study from Scotland, that showed The Delta Variant, was about twice as likely as, The Alpha Variant, to result in hospitalization, in Unvaccinated Individuals, but, other data has shown, no significant differences.

Another question focuses on, how The Delta Variant, affects the body. There have been reports of symptoms, that are different, than those associated, with the Original COVID-19 Strain, Dr. Yildirim says. “It seems like cough and loss of smell, are less common, headache, sore throat, runny nose and fever, are present, based on the most recent surveys in the U.K., where more than 90%, of the Cases, are due to the Delta Variant's Strain,” she says.

It’s unclear, whether The Delta Variant, could cause more Breakthrough Cases with infections, in people who have been Vaccinated or have A Natural Immunity, from a prior COVID-19 Infection. This question is being revisited, after the Provincetown Outbreak. “Breakthrough is a big question,” Dr. Wilson says. “At least with Immunity, from the MRNA Vaccines, it doesn’t look, like it will be a problem.” A Public Health England Analysis (In a preprint, that has not yet been peer-reviewed) and shown that, at least two Vaccines are effective, against The Delta Variant. The Pfizer-BioNTech Vaccine was 88% effective, against symptomatic diseases and 96% effective, against hospitalizations, from The Delta Variant, in the studies, while Oxford AstraZeneca, (which is not an MRNA Vaccine) was 60% effective, against symptomatic disease and 93% effective against hospitalizations. The studies tracked participants, who were fully Vaccinated, with both of the recommended doses.

Moderna, has also reported on studies (not yet peer-reviewed) that showed, its Vaccine, to be effective, against The Delta Variant and from Several Other Mutations, (researchers noted, only a ”modest reduction in Neutralizing Titers,” against The Delta Variant, when compared to its effectiveness against the Original COVID-19).

“So, your risk is significantly lower, than someone who has not been Vaccinated and you are safer than you were, before you got your vaccines,” Dr. Yildirim says.

Will Vaccinated People need Booster Shots to protect against The Delta Variant? Some experts say, it’s too soon to know, whether we will need a Booster modified to target The Delta Variant or to bolster protection against the Original COVID-19. But both Pfizer and Moderna, are working on boosters, although, they would still face the hurdle, of getting FDA Authorization for them. While the Biden Administration Officials have not made a commitment to boosters, in July, it said a third shot of the two MRNA Vaccines, might be necessary for people over 65 years of age and those with Compromised Immune Systems.

Johnson & Johnson also has reported that its Vaccine, is effective against The Delta Variant, but one recent study, which has not yet been peer-reviewed or published in a scientific journal, suggests that its Vaccine, is less effective against The Delta Variant, which has prompted discussion, over whether or not, J&J Recipients, might also, need a Booster.

There are additional questions and concerns about The Delta Variant, including The Delta Variant Plus, A Sub-Variant Of The Delta Variant, that has been found in the U.S., the U.K. and in, other countries. “The Delta Variant Plus, has one additional mutation, to what The Delta Variant has,” says Dr. Yildirim. This mutation, called K417N, affects the Spike Protein, that The COVID-19 Virus, needs to infect cells and that is the main target, for the MRNA and other Vaccines, she says.

“Delta Plus Variant, has been reported first in India, but, the type of mutation, was reported in Variants, such as: The Beta Variant, that emerged earlier. More data is needed to determine, the actual rate of spread and impact of this New Variant on Disease Burdens and Outcomes,” Dr. Yildirim adds.

5. Vaccination Is The Best Protection Against The Delta Variant:

The most important thing you can do to protect yourself, from The Delta Variant, is to get fully Vaccinated, the doctors say. At this point, that means, if you get a Two-Dose Vaccine, like The Pfizer or The Moderna, for example, you must get both shots and then wait, the recommended two-week period, for those shots to take full effect. Whether or not you are Vaccinated, it’s also important, to follow the CDC's Prevention Guidelines, that are available for Vaccinated and Unvaccinated People.

“Like everything in life, this is an ongoing risk assessment,” says Dr. Yildirim. “If it is sunny and you’ll be outdoors, you put on, sunscreen. If you are in a crowded gathering, potentially with Unvaccinated People, you put your mask on and keep Social Distancing. If you are Unvaccinated and eligible for the Vaccine, the best thing you can do is, to get, Vaccinated.”

Face masks can provide additional protection and the WHO, has encouraged mask-wearing even among, Vaccinated People. The CDC updated its Guidance, in July to recommend that both Vaccinated and Unvaccinated individuals, wear masks in public, indoor settings, in areas of high transmission to help prevent The Delta Variant’s spread and to protect others, especially those who are Immunocompromised, Unvaccinated, or at risk for severe disease. The agency is also recommending that universal, indoor masking for all teachers, staff, students and visitors to K-12 schools.

Of course, there are many people who cannot get the Vaccine, because their doctor has advised them against it, for health reasons or because personal logistics or difficulties, have created roadblocks or they may choose, not to get it. Will The Delta Variant, be enough to encourage those who can get Vaccinated, to do so? No one knows for sure, but it’s possible, says Dr. Wilson, who encourages anyone, who has questions about Vaccinations, to talk to their family doctor.

“When there are Local Outbreaks, Vaccine Rates go up,” Dr. Wilson says. “We know, that if someone you know, gets really sick and goes to the hospital, it can change your risk calculus, a little bit. That could start happening more. I’m hopeful that we will see, The Vaccine Rates, go up.”

Katella, Kathy. “5 Things To Know About the Delta Variant.” Yale Medicine. Originally published: June 28th, 2021. Updated: August 3rd, 2021. Please see:

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