Understanding Vaccine Protection Against Delta Variant

The Delta variant of the coronavirus, known for its high transmissibility, has made its way to over 174 countries, including the United States and Australia, leading to a rise in COVID-19 cases. This variant possesses mutations that may enable it to partially evade the immune defenses established by vaccines.

The effectiveness of COVID-19 vaccines against the Delta variant is not straightforward. Evidence suggests that these vaccines might provide reduced protection against symptomatic infections caused by Delta when compared to other variants.

According to a report from Public Health England, released on September 9, COVID-19 vaccines showed approximately 79% efficacy against symptomatic cases linked to the Delta variant after two doses.

Efficacy of Vaccines: Insights from Recent Studies

Recent research highlights the varying levels of effectiveness of different vaccines against symptomatic infections caused by the Delta variant.

#### UK Study: Efficacy Rates for Pfizer and AstraZeneca

A study conducted in the UK and published in the New England Journal of Medicine on July 21 revealed that both AstraZeneca and Pfizer vaccines demonstrated significant effectiveness against the Delta variant from two weeks post-second dose. The findings were:

• Pfizer: 33% effective after one dose; 88% after two doses.
• AstraZeneca: 33% effective after one dose; 67% after two doses.

#### Canadian Analysis: Pfizer and Moderna Performance

A Canadian study released on July 3 found that two doses of either Pfizer or Moderna vaccines were comparably effective against Delta as they were against the Alpha variant. The results indicated:

• Pfizer: 56% effective from 14 days after the first dose; 87% effective after two doses.
• AstraZeneca: 67% effective from 14 days post-first dose; insufficient data for two doses.
• Moderna: 72% effective from 14 days after the first dose; insufficient data for two doses.

#### Israel's Findings: Pfizer's Efficacy

On July 6, the Israel Ministry of Health reported that the effectiveness of Pfizer's vaccine against the Delta variant was slightly lower than earlier estimates. The study noted:

• Pfizer: 64% effective after two doses.

#### Scotland's Research: Protection Levels

A letter published in the Lancet on June 14 from a Scotland-based study reported that:

• Pfizer: 79% effective after two doses, at least 14 days following the second dose.
• AstraZeneca: 60% effective after two doses, at least 14 days post-second dose.

Broader Studies on Asymptomatic Infections

Two significant studies have assessed vaccine effectiveness against all COVID-19 infections, including asymptomatic cases.

• Qatar Study: Reported Pfizer's effectiveness at 53.5% after two doses and Moderna at 84.8% after two doses.
• UK Study: Found Pfizer at 80% effective after two doses and AstraZeneca at 67% after two doses.

Factors Influencing Variability in Vaccine Effectiveness

Determining the real-world effectiveness of vaccines presents challenges compared to controlled trials. Factors such as the demographics of vaccinated individuals, previous COVID-19 infections, and their exposure to risk influence the results.

Professor Stephen Evans from the London School of Hygiene & Tropical Medicine indicated that generally, the severity of illness caused by Delta correlates with vaccine effectiveness; however, the overall evidence remains inconclusive.

This report was updated on September 13, 2021, to include new findings regarding vaccine performance against the Delta variant.

If you have insights or stories related to the pandemic, feel free to reach out at [email protected].

Chapter 2: Vaccination and Delta Variant Dynamics

The first video discusses the effectiveness of the Johnson & Johnson vaccine against the Delta variant, providing insights into its performance based on recent studies.

The second video examines the regions in the U.S. where the Delta variant shows the highest transmission rates, shedding light on its impact across different states.