# Delta Variant: A Growing Concern for Vaccinated Individuals
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Chapter 1: Understanding the Delta Variant
The Delta variant is raising significant alarms among health experts, particularly regarding its impact on vaccinated individuals. Some researchers express concerns that Delta could lead to an uptick in breakthrough infections—instances where fully vaccinated people contract COVID-19. There’s also anxiety surrounding its potential to evolve into a more dangerous variant.
On April 15, scientists at the University Hospital of Badajoz in Spain were busy sequencing coronavirus samples. As Bob Wachter, chair of the Department of Medicine at the University of California, San Francisco, noted, experts have long feared a variant that could outpace the original virus in three critical aspects: transmissibility, severity of illness, and vaccine resistance.
“Imagine a variant that excels in all three areas,” Wachter cautioned. “So far, no variant has succeeded in more than one or two, but Delta, which emerged in India in February, has come alarmingly close.”
According to Wachter, current data indicates that Delta is highly contagious, likely leads to more severe cases, and shows some capacity to evade vaccine protection, which is concerning. The Centers for Disease Control and Prevention (CDC) has since classified Delta as a "variant of concern."
“Delta is the most contagious variant we've encountered so far, a true superspreader,” tweeted Eric Topol, director of the Scripps Research Translational Institute.
Section 1.1: Breakthrough Infections and Evolving Threats
While Delta primarily threatens the unvaccinated, experts also worry about the possibility of increased breakthrough infections among those who are vaccinated. “The concern is that exposure to the virus might lead to a COVID-19 infection even after full vaccination,” Wachter stated. “Moreover, if you contract COVID, there's a higher chance of experiencing severe symptoms.”
Additionally, some experts fear that Delta’s rapid spread could lead to further mutations, resulting in a variant that is even harder to control. “The worst-case scenario would be a mutation that makes our current vaccines less effective or even ineffective,” warned Vivek Cherian, an internal-medicine physician in Baltimore.
Subsection 1.1.1: Understanding Delta's Transmissibility
Research from Public Health England indicates that Delta is associated with a 60% higher risk of household transmission compared to the Alpha variant, which itself was already 50% more transmissible than the original strain. This suggests that Delta’s transmissibility is significantly heightened.
Wachter explained, “If Alpha is compared to the original strain, Delta is to Alpha what a Ferrari is to a sedan.” Furthermore, studies from Scotland reveal that infection with Delta doubles the risk of hospital admission compared to Alpha.
Nevertheless, vaccines have largely held up against Delta. Analyses show that two doses of Pfizer's vaccine maintain a 96% efficacy rate against hospitalizations and an 88% effectiveness against symptomatic COVID-19 caused by Delta. AstraZeneca’s two doses provide around 92% protection against hospitalizations and 60% against symptomatic cases. However, the efficacy of a single dose drops to just 33%.
“The stark difference in protection levels post-first dose indicates that Delta has managed to partially circumvent our immune defenses,” Wachter remarked.
Section 1.2: The Risk of Breakthrough Cases
Despite variants being responsible for most breakthrough cases, actual occurrences remain rare. A CDC report from May noted that only 0.01% of fully vaccinated Americans contracted COVID-19. Cherian believes that breakthrough infections with Delta should not be a major worry; however, Wachter feels that the variant might escalate mild cases into more serious infections.
“The risk is particularly pronounced for elderly and immunocompromised individuals,” he warned. “The immune response of an 80-year-old who has been vaccinated is not comparable to that of a 30-year-old.”