How Does the COVID Delta Variant Compare?
In late 2020, a variant of COVID-19 was detected in India that began to quickly spread.
Soon after it received the label “Delta,” it started to become the predominant strain of COVID-19 in countries of transmission. It spread faster than both the original disease and other variants, including “Alpha” that had taken hold in the UK.
Now the COVID-19 pandemic has essentially become the Delta pandemic, as the variant accounts for more than 90% of global cases.
But how does the COVID-19 Delta variant differ from the original disease? We consolidated studies as of September 2021 to highlight key differences between COVID-19 and the dominant variant. Sources include the CDC, Yale Medicine, and the University of California.
COVID-19 vs COVID-19 Delta Variant
At first glance, infections caused by the Delta variant are similar to the original COVID-19 disease. Symptoms reported from patients include cough, fever, headache, and a loss of smell.
But studies showed that the difference was in how quickly and severely patients got sick:
- Spread rate: How quickly the infection spreads in a community (based on the R0 or basic reproductive number). The Delta variant spread 125% faster than the original disease, making it potentially as infectious as chickenpox.
- Viral load: How much of a virus is detectable in an infected person’s blood, with higher loads correlating with more severe infections. Delta infections had a 1000x higher viral load.
- Virus detectable: How long after exposure a virus is detectable in an infected person’s blood. Delta infections were found to be detectable four days after exposure, faster than the original disease (six days).
- Infectious period: How long an infected person has the capability to pass on the virus to other people, from the first time they were exposed. Delta infections were contagious for longer than traditional COVID-19 infections, at 18 days compared to 13 days.
- Risk of hospitalization: How much more or less likely is an infection going to require hospitalization for treatment? Infections caused by the Delta variant were twice as likely to cause hospitalization compared to the original disease.
One other important finding from studies was that the existing COVID-19 vaccines helped against Delta infections.
The CDC found that approved vaccines reduced the rate of infection by 5x and the rate of hospitalization by 29x in a breakthrough case. They also found that overall efficacy against infection can wane over time, however, and at-risk people might require a booster vaccine.
What About Other COVID-19 Variants?
Delta is just one of many COVID-19 variants tracked by health officials, but it’s the one we know the most about.
That’s because reliable statistics and information on diseases requires thousands of cases for comparisons. We know a lot about Delta (and the once-dominant UK strain Alpha) because of how widespread they became, but there haven’t been enough cases of other variants to reliably assess differences.
As of September 2021, WHO was tracking 20 COVID-19 variants around the world with different classifications based on potential severity:
- 14 Variants under monitoring (VUM): Variants that are deemed to not pose a major global health risk, or no longer pose one.
- 2 Variants of Interest (VOI): Variants that affect transmissibility, virulence, mutation, and other virus characteristics, and are spreading in clusters.
- 4 Variants of Concern (VOC): Have similar characteristics to VOI but are further associated with a global risk.
Most of the current variants of interest and concern were first identified and labeled in late 2020, though 2021 variants are showing up as well.
|Label||Designation||Documented Origin||Earliest Identified Date|
|Alpha||Variant of Concern||UK||September 2020|
|Beta||Variant of Concern||South Africa||May 2020|
|Gamma||Variant of Concern||Brazil||November 2020|
|Delta||Variant of Concern||India||October 2020|
|Lambda||Variant of Interest||Peru||December 2020|
|Mu||Variant of Interest||Colombia||January 2021|
Should you be worried about all of these variants? For the most part, a lack of cases to provide clear information also reflects that they’re equivalent to or weaker than traditional COVID-19 infections.
But it’s important to note that our understanding of diseases and variants becomes more nuanced and accurate over time. As research continues over a longer timeline and over a wider database of cases, expect information on COVID-19 variants (and any disease) to become more concrete.
Visualizing the Relationship Between Cancer and Lifespan
New research links mutation rates and lifespan. We visualize the data supporting this new framework for understanding cancer.
A Newfound Link Between Cancer and Aging?
A new study in 2022 reveals a thought-provoking relationship between how long animals live and how quickly their genetic codes mutate.
Cancer is a product of time and mutations, and so researchers investigated its onset and impact within 16 unique mammals. A new perspective on DNA mutation broadens our understanding of aging and cancer development—and how we might be able to control it.
Mutations, Aging, and Cancer: A Primer
Cancer is the uncontrolled growth of cells. It is not a pathogen that infects the body, but a normal body process gone wrong.
Cells divide and multiply in our bodies all the time. Sometimes, during DNA replication, tiny mistakes (called mutations) appear randomly within the genetic code. Our bodies have mechanisms to correct these errors, and for much of our youth we remain strong and healthy as a result of these corrective measures.
However, these protections weaken as we age. Developing cancer becomes more likely as mutations slip past our defenses and continue to multiply. The longer we live, the more mutations we carry, and the likelihood of them manifesting into cancer increases.
A Biological Conundrum
Since mutations can occur randomly, biologists expect larger lifeforms (those with more cells) to have greater chances of developing cancer than smaller lifeforms.
Strangely, no association exists.
It is one of biology’s biggest mysteries as to why massive creatures like whales or elephants rarely seem to experience cancer. This is called Peto’s Paradox. Even stranger: some smaller creatures, like the naked mole rat, are completely resistant to cancer.
This phenomenon motivates researchers to look into the genetics of naked mole rats and whales. And while we’ve discovered that special genetic bonuses (like extra tumor-suppressing genes) benefit these creatures, a pattern for cancer rates across all other species is still poorly understood.
Cancer May Be Closely Associated with Lifespan
Researchers at the Wellcome Sanger Institute report the first study to look at how mutation rates compare with animal lifespans.
Mutation rates are simply the speed at which species beget mutations. Mammals with shorter lifespans have average mutation rates that are very fast. A mouse undergoes nearly 800 mutations in each of its four short years on Earth. Mammals with longer lifespans have average mutation rates that are much slower. In humans (average lifespan of roughly 84 years), it comes to fewer than 50 mutations per year.
The study also compares the number of mutations at time of death with other traits, like body mass and lifespan. For example, a giraffe has roughly 40,000 times more cells than a mouse. Or a human lives 90 times longer than a mouse. What surprised researchers was that the number of mutations at time of death differed only by a factor of three.
Such small differentiation suggests there may be a total number of mutations a species can collect before it dies. Since the mammals reached this number at different speeds, finding ways to control the rate of mutations may help stall cancer development, set back aging, and prolong life.
The Future of Cancer Research
The findings in this study ignite new questions for understanding cancer.
Confirming that mutation rate and lifespan are strongly correlated needs comparison to lifeforms beyond mammals, like fishes, birds, and even plants.
It will also be necessary to understand what factors control mutation rates. The answer to this likely lies within the complexities of DNA. Geneticists and oncologists are continuing to investigate genetic curiosities like tumor-suppressing genes and how they might impact mutation rates.
Aging is likely to be a confluence of many issues, like epigenetic changes or telomere shortening, but if mutations are involved then there may be hopes of slowing genetic damage—or even reversing it.
While just a first step, linking mutation rates to lifespan is a reframing of our understanding of cancer development, and it may open doors to new strategies and therapies for treating cancer or taming the number of health-related concerns that come with aging.
Explainer: What to Know About Monkeypox
What is monkeypox, and what risk does it pose to the public? This infographic breaks down the symptoms, transmission, and more.
Explainer: What to Know About Monkeypox
The COVID-19 pandemic is still fresh in the minds of the people around the world, so it comes as no surprise that recent outbreaks of another virus are grabbing headlines.
Monkeypox outbreaks have now been reported in multiple countries, and it has scientists paying close attention. For everyone else, numerous questions come to the surface:
- How serious is this virus?
- How contagious is it?
- Could monkeypox develop into a new pandemic?
Below, we answer these questions and more.
What is Monkeypox?
Monkeypox is a virus in the Orthopoxvirus genus which also includes the variola virus (which causes smallpox) and the cowpox virus. The primary symptoms include fever, swollen lymph nodes, and a distinctive bumpy rash.
There are two major strains of the virus that pose very different risks:
- Congo Basin strain: 1 in 10 people infected with this strain have died
- West African strain: Approximately 1 in 100 people infected with this strain died
At the moment, health authorities in the UK have indicated they’re seeing the milder strain in patients there.
Where did Monkeypox Originate From?
The virus was originally discovered in the Democratic Republic of Congo in monkeys kept for research purposes (hence the name). Eventually, the virus made the jump to humans more than a decade after its discovery in 1958.
It is widely assumed that vaccination against another similar virus, smallpox, helped keep monkeypox outbreaks from occurring in human populations. Ironically, the successful eradication of smallpox, and eventual winding down of that vaccine program, has opened the door to a new viral threat. There is now a growing population of people who no longer have immunity against the virus.
Now that travel restrictions are lifting in many parts of the world, viruses are now able to hop between nations again. As of the publishing of this article, a handful of cases have now been reported in the U.S., Canada, the UK, and a number of European countries.
On the upside, contact tracing has helped authorities piece together the transmission of the virus. While cases are rare in Europe and North America, it is considered endemic in parts of West Africa. For example, the World Health Organization reports that Nigeria has experienced over 550 reported monkeypox cases from 2017 to today. The current UK outbreak originated from an individual who returned from a trip to Nigeria.
Could Monkeypox become a new pandemic?
Monkeypox, which primarily spreads through animal-to-human interaction, is not known to spread easily between humans. Most individuals infected with monkeypox pass the virus to between zero and one person, so outbreaks typically fizzle out. For this reason, the fact that outbreaks are occurring in several countries simultaneously is concerning for health authorities and organizations that monitor viral transmission. Experts are entertaining the possibility that the virus’ rate of transmission has increased.
Images of people covered in monkeypox lesions are shocking, and people are understandably concerned by this virus, but the good news is that members of the general public have little to fear at this stage.
I think the risk to the general public at this point, from the information we have, is very, very low.
–Tom Inglesby, Director, Johns Hopkins Center for Health Security
» For up-to-date information on monkeypox cases, check out Global.Health’s tracking spreadsheet
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