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All About The Delta Variant

Doctorpedia Editorial Team Doctorpedia Editorial Team
Medically reviewed by Susan Kerrigan, MD and Marianne Madsen

The COVID-19 pandemic has been with us now for over a year. In recent months, some light was finally beginning to be seen at the end of the tunnel. Vaccination rates were steadily rising, infection rates were falling, and we began to believe that we may be at the beginning of the end of the pandemic. However, more recently, new variants have emerged that have raised concern levels among health experts and seen an increase in infections and hospitalization rates. Today, the coronavirus variant of most concern is the COVID-19 Delta variant.


Before discussing the Delta variant, it is worth making the point that viruses change and mutate. That’s how they survive. Variants from the original strain are common.


Variant classifications


The Centers for Disease Control and Prevention (CDC) has a three-tiered classification system where they assess the impact of variants. Suppose a variant might lead to an outbreak but hasn’t yet become widespread. In that case, the CDC classifies it as a “variant of interest.” The next tier is when the variant shows signs of increasing disease severity and becoming more easily transmitted. The CDC considers this to be a “variant of concern.” The final category is reserved for a variant that reduces the effectiveness of treatment and the existing vaccines. This variant is classified as a “variant of high consequence.”


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Delta Variant - What Is It?

Delta Variant - What Is It?

What is the Delta variant?


The B.1.617.2 COVID-19 variant was first discovered in India. It was subsequently given the label of “Delta” by the World Health Organization (WHO) as part of its revised non-numeric classification system for coronavirus variants. The CDC currently classifies it as a “variant of concern.” This classification is based on evidence that it is a more easily transmissible variant and that current vaccination and treatment methods may be less effective against it.


The Delta variant is now the dominant strain in the US, making up a predicted 82.2% of all coronavirus cases.


What are the most common symptoms of the Delta variant?


Based on the spread of the variant in other countries worldwide, the symptoms of the Delta variant are different and more severe than previous strains of the virus. In the UK, where Delta is by far the dominant variant making up 98% of coronavirus cases in July, the most reported symptoms are headache, runny nose, and sneezing.


How contagious is the Delta variant?


Data from the UK suggests that the Delta variant could be between 40-60% more infectious than the Alpha strain discovered in England earlier this year.


Are the effects of the Delta variant more severe than previous strains?


Based on the official data from Public Health England (PHE), it appears that the biggest difference between the Delta variant and the previously reported Alpha variant is increased hospitalization. According to a report published by PHE in June, a person with the Delta variant is 2.61 times more likely to be hospitalized than one with the Alpha variant.


Are current vaccines effective against the Delta variant?


Due to limited current research, it is not yet possible to fully assess the effectiveness of vaccines against the Delta variant. However, in an analysis published by PHE in June, both the Pfizer-BioNTech vaccine and AstraZeneca vaccine remained as effective against hospitalization after two doses compared to the Alpha variant. 


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Delta Variant - Effectiveness of Vaccines

Delta Variant - Effectiveness of Vaccines

A previous study by PHE, published in May, also compared the effectiveness of the existing COVID-19 vaccines against symptomatic disease from the Delta variant. After two doses, the data showed that the Pfizer vaccine was 88% effective, slightly lower than the numbers for the Alpha variant but still offering adequate protection. The figures for the AstraZeneca vaccine were also slightly lower for the Delta variant than for the Alpha. However, the biggest difference was in the degree of protection after a single dose. Both vaccines only managed 33% effectiveness against symptomatic infection three weeks after the first dose, a drop of 17% compared to the Alpha variant. This potential reduction in effectiveness highlights the importance of getting both doses of a two-dose vaccine.


Other COVID-19 vaccines have also been analyzed for their effectiveness against the Delta variant. The interim results from laboratory studies have not yet been fully verified and peer-reviewed. However, they suggest that the Moderna and Johnson & Johnson vaccines also have similarly high levels of effectiveness.


The official position of the US Surgeon General, Dr. Vivek H. Murthy, which he reiterated at a recent White House press briefing, is that vaccination is the only way to control the virus. According to Dr. Murthy, 99.5% of COVID-19 deaths and 97% of the possible hospitalizations are among unvaccinated people. 


The best way to protect yourself against the Delta variant and any other future or current variants of COVID-19 is to follow the WHO and CDC’s guidelines and make sure you get fully vaccinated.

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