Study: One Dose of AstraZeneca or Moderna Vaccine Was Effective in Preventing Hospitalizations and Death from New Variants

A study in Canada showed that one dose of the Oxford / AstraZeneca, Moderna and Pfizer / BioNTech coronavirus vaccines was effective in preventing hospitalizations and deaths against the alpha, beta, gamma and delta variants of concern.

The work, which is in pre-print – meaning it has not yet been published in a peer-reviewed scientific journal – at (https://www.medrxiv.org/content/10.1101/2021.06. 28.21259420v2), aimed to determine the efficacy of the vaccine in preventing symptomatic cases, hospitalizations and deaths of these four variants.

To do this analysis, Ontario residents aged 16 or older who lived in the community and had symptoms compatible with Covid-19 were included, who underwent the SARSCoV-2 test between December 14, 2020 and December 30. May 2021.

“Our results suggest that even a single dose of these three vaccines provides substantial protection against these 4 VOCs, and 2 doses are likely to provide greater protection,” noted the authors.

They also noted that “jurisdictions facing vaccine supply limitations may consider delaying second doses to achieve better overall protection of the population more quickly.”

To conduct the study, the researchers used “a negative test design to compare vaccine status between positive tests from individuals with symptomatic or severe and symptomatic infection but who test negative.”

During this period, 421,073 symptomatic individuals residing in the community were identified, of which 69,533 were positive: 28,705 (6.8%) had no variant of concern and 40,828 (9.7%) had one of the four worrying variants studied.

During this period, 14,168 people hospitalized or died from Covid-19 were also recorded, mainly with the Delta variant, detected for the first time in India.

Researchers found that one dose of Pfizer and Moderna vaccines was 55% and 70% effective against symptomatic infections caused by the variants of concern circulating in Ontario, Canada, respectively.

While vaccination with one dose of AstraZeneca prevented almost half of symptomatic cases of the Beta (first detected in South Africa) and Gamma (first detected in Brazil) variants, over 60% against Alpha (first detected in UK) and Delta.

The study found that “the efficacy of partial (one-dose) vaccination was significantly higher against hospitalization or death than against symptomatic infection” in all vaccines compared to all variants.

In particular, against Delta, the vaccine efficacy against severe outcomes (hospitalization or death) after a dose of Pfizer, Moderna and AstraZeneca was 78%, 96% and 88%, respectively.

As a limitation, the authors acknowledge that “the classification of variants in this study was based on a combination of mutation detection and whole genome sequencing, and the criteria for sequencing have evolved throughout the pandemic.”