COVID-19 vaccine effectiveness against SARS-CoV-2 variants

A commentary published in the journal Cell summarizes international data on vaccine effectiveness against new severe acute respiratory coronavirus 2 (SARS-CoV-2) variants. Evidence shows that the currently approved vaccines continue to be effective in preventing severe and symptomatic illness — even with the widely circulating Delta variant.

SARS-CoV-2 has mutated many times in the pandemic. As a result, it can accumulate new mutations quickly that may help increase transmission, escape neutralizing antibodies, or increase infection severity.

The scientists from the University of St Andrews, Yale School of Public Health, and Imperial College London say that SARS-CoV-2 will continue producing mutations promoting immune evasion, but vaccine-induced immunity could be the best way to counter this. Therefore, monitoring variants and the global distribution of COVID-19 vaccines will be crucial in addressing the pandemic.

Study: COVID-19 vaccines: Keeping pace with SARS-CoV-2 variants. Image Credit: NIAID

Vaccine effectiveness against the Alpha variant

On several occasions, the Alpha variant has been shown to possess a mutation, allowing it to evade the immune system.  However, evasion of vaccine-induced immunity is limited. Furthermore, real-world data suggest vaccines remain highly effective in reducing the spread of Alpha and preventing severe infection.

Against the Novavax vaccine, there was an 86% efficacy against Alpha. The Pfizer-BioNTech vaccine was 92% effective in preventing asymptomatic infection, 97% effective against symptomatic infection, and 97% against severe illness.

Research from Scotland showed that the administration of the AstraZeneca and Pfizer-BioNTech vaccine resulted in a 94% and 85% decrease in coronavirus-related hospital admissions, respectively.

Studies from Qatar showed the Pfizer-BioNTech vaccine had an 89.5% protection from Alpha-induced infection. Additionally, the Pfizer-BioNTech vaccine was 97.4% effective against severe infection.

Vaccine effectiveness against the Beta variant

Research investigating vaccine effectiveness for the Pfizer-BioNTech full dose regimen occurred in South Africa, where the Beta variant is dominant. Early results suggested a high level of protection against symptomatic infection, and no COVID-19 cases were reported in the vaccine group.

In Qatar, the Beta reduced vaccine effectiveness after one dose of the Pfizer-BioNTech. But receiving a second dose produced a 75% protection against Beta-induced infection and 97.4% protection against severe illness.

The Johnson & Johnson vaccine clinical trials in South Africa showed a 65% to 66% protection against hospitalization. Similar to findings from the United States, the Johnson & Johnson shot was 91%-95% effective against COVID-19–induced mortality.

The Beta variant did somewhat reduce vaccine effectiveness but not completely. The Novavax vaccine showed reduced protection against mild-to-moderate COVID-19 illness with the Beta variant.

The AstraZeneca vaccine decreased to 60% protection against mild and moderate COVID-19 infection. But the researchers point out that the result mentioned above came from a small phase 1/2a trial that more focused on safety than vaccine effectiveness. Therefore, AstraZeneca’s vaccine effectiveness against the Beta variant is still under investigation. It’s also unknown whether delaying the second AstraZeneca shot provides a better antibody response against Beta.

Gamma variant versus vaccines

The Gamma variant was first reported in Brazil and has a mutation promoting immune evasion. Research into vaccine effectiveness from the Sinovac and the AstraZeneca vaccines shows similar protection against symptomatic COVID-19 infection.

Vaccines continue to protect against dominant Delta variant

Real-world data in multiple countries suggests vaccines continue to protect against hospitalization and symptomatic infection.

With Delta rapidly circulating in England, researchers have observed that the Pfizer-BioNTech and Johnson & Johnson vaccines are 96% and 92% protective against hospitalization.

The mRNA vaccines continue to show high protection as well. For example, despite Delta being the dominant SARS-CoV-2 in the New York area, there was a 91.9%-95.3% protection against hospitalization.

In England and Canada, one vaccine dose was less protective against the Delta variant than the Alpha variant. However, vaccine effectiveness increased after the second dose. The Pfizer-BioNTech vaccine was 85%-90% effective, and the AstraZeneca vaccine was 61%-72% effective.

Early data from Israel’s Ministry of Health drew concerns of vaccines being less effective against symptomatic Delta infection. However, the researchers note this data may have been unreliable. “…further preprint published research did not report effectiveness figures against symptomatic infection as symptoms reporting was not reliable in the national database. Vaccine effectiveness against infection is much harder to measure as these estimates are affected by various biases such as testing criteria, behavior, exposure risk, immunity status of the population, and community prevalence.”

Later studies have shown a slight decline in vaccine-induced protection, but the researchers note the analyses did not account for infections already present in unvaccinated people.


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