The Delta variant

The Delta variant is the predominant variant of the SARS-CoV-2 (COVID-19) virus, currently accounting for more than 90% of diagnosed cases. The variant is much more contagious, more transmissible, and may cause more severe infection.

What makes the Delta variant different?

The Delta variant is much more contagious than earlier strains of COVID-19.

One of the major differences between the COVID-19 delta variant and the COVID-19 alpha variant and original strain is how quickly it is spreading. Data has confirmed that people infected with the delta variant carry about 1,000 times the amount of virus in their nasal canals compared to those infected with other variants.

According to the Centers for Disease Control and Prevention (CDC), Delta is more transmissible than the common cold and influenza, as well as the viruses that cause smallpox, MERS, SARS, and Ebola.

Because it’s so much more contagious, the variant can be easily spread between both unvaccinated and vaccinated people, even if they don’t show any symptoms.

Workers in hardhats wearing protective masks

Why is the Delta variant more contagious?

The shape of the COVID-19 Delta variant makes it more contagious.

Researchers have figured out the key to why the Delta variant is so much more contagious. It has to do with the physical shape of the virus itself.

Because of the different structure of the spike protein, the Delta variant infects lung cells more easily, making it the most contagious version of the coronavirus in the world.

Higher levels of reproduction.

The unique shape of the spike protein found in the Delta variant not only causes it to grow more rapidly inside people’s respiratory tracts, it also allows it to reproduce virus at much higher levels. On average, people infected with the Delta variant carry about 1,000 times the amount of virus in their respiratory tracts compared to those infected with other variants.

Becoming infectious sooner.

Along with carrying higher amounts of viral load, people with the COVID-19 Delta variant are also likely to become infectious sooner. With the original COVID-19 strain, it took an average of six days to reach detectable levels. With the Delta variant, that time is reduced to only four days.

The R0 (“R naught”) tracking metric.

In an effort to create a baseline and provide a standardized way to track how easily an infectious disease such as COVID-19 spreads, a metric called the basic reproductive number or R0 (pronounced “R naught”) was created. R0 is the average number of susceptible people that each infected person is expected to infect. The higher the R0, the more infectious the disease. If a disease has an R0 less than one, the disease will stop spreading naturally and will likely go away on its own.

The Delta variant’s high R0 value.

For historical context, the R0 for the 1918 Spanish influenza pandemic was between 2.0 and 3.0 and the R0 for the first SARS coronavirus epidemic of 2002 had an R0 of 3.0. The R0 for the standard yearly flu is around 2.0.

With relation to the current COVID-19 virus, the R0 for the Delta variant is between 6.0 and 7.0. This means that one person infected with the COVID-19 Delta variant can infect 6-7 people, who then can each go on to infect another 6-7 people, and so on. This is nearly double that of the original strain of COVID-19, which had an R0 of between 2.0 and 3.0.

While that may not seem like a huge jump, when you consider the exponential way in which viruses spread, it’s a massive difference that indicates the end of the pandemic may very well rest on the willingness of large amounts of the population to get vaccinated.

Why is the Delta variant dangerous?

The COVID-19 Delta variant is dangerous because it’s a more contagious mutation of the original strain of COVID-19 virus that has caused a spike in hospitalizations around the nation. At this time, there is still some debate as to whether the variant is associated with worse clinical outcomes. Specifically, it is not known if more people are getting sick because of a combination of high case numbers among vulnerable populations, or low vaccination rates. There also could be impact on patient care and outcomes related to increased stress on hospital systems.

Young children at school wearing masks - COVID-19 delta variant - UCHealth

As more and more data are collected, however, it appears that people infected with the COVID-19 delta variant experience different symptoms than those experienced with other strains. With that being said, there’s no indication that the associated symptoms are more severe in nature.

Common symptoms of those infected with the COVID-19 delta variant include fever, headache, sore throat, and runny nose. Unlike the original strain of COVID-19, cough and loss of smell are not common symptoms.

Other reports link the variant to more serious symptoms, including hearing impairment, severe gastrointestinal issues and blood clots leading to tissue death and gangrene.

Being vaccinated does not mean that you cannot become infected with the COVID-19 delta variant. Symptoms can be milder in vaccinated individuals, so we encourage testing even if you think the symptoms are due to allergies.

Frequently asked questions (FAQs) about the Delta variant of COVID-19

With infection from any respiratory virus, including the flu, there is always a small probability for death. The same is true for COVID-19 and all its variants. The COVID-19 delta variant hasn’t been proven to be more lethal than other variants, but it has an even greater potential to kill people simply by the large numbers of people it can infect due to its ease of transmission.

As of August 2021, the U.S. mortality rate is around 1% for those infected with COVID-19.

COVID-19 is transmitted via respiratory droplets that are generated whenever an infected individual coughs or sneezes. According to the CDC, the risk of contracting any form of COVID-19 through contact with a surface or with food is very low.

The CDC and local health departments have been sequencing the virus from people who test positive for COVID-19 since the beginning of the pandemic. They do not sequence every single person, but do sequence a huge number of them. Based on this, they are able to see which variants are circulating.

According to the CDC and CDPHE websites, the predominant variant right now is Delta at almost 98%. Given that, if you test positive for COVID-19 right now, you can assume that it is likely to be Delta.

Estimates are that people infected with the COVID-19 Delta variant and are mildly ill are contagious no more than 10 days after symptom onset, whereas people who are moderately to severely ill or are immunocompromised can be contagious up to 20 days after symptom onset.

Recovery time depends on multiple factors, including the severity of the infection and the overall health of the person infected.

Generally speaking, a healthy person infected with the delta variant can expect to need at least two weeks to recover from a mild illness to six weeks or more to recover from a more severe infection.

In people who have had COVID-19 and recovered, studies have shown that immunity lasts roughly 6 to 8 months after onset of symptoms.