During the time that vaccination schemes were being scaled up in Qatar, around February 2021, two severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern rose to dominance in the country: B.1.1.7 and B.1.351.
The Moderna SARS-CoV-2 vaccine was widely distributed and had a reported efficacy in clinical trials of 94.1% against the wildtype SARS-CoV-2 following the second dose administration. Therefore, Chemaitelly et al. used this as an opportunity to measure the vaccine’s efficacy against these variants as reported in a recent Nature Medicine paper, finding that the vaccine has good efficacy in all aspects.
Qatar has a young and diverse demographic, with only 9% of residents being over 50 and a majority having immigrated from another country, making it an interesting population to draw epidemiological data regarding the efficacy of vaccines.
The research group utilized national statistics data, including PCR and subsequent Sanger sequencing for full genomic identification. Weekly rounds of random testing collected 3,924 specimens for identification, giving approximate proportions for B.1.351 and B.1.1.7 amongst the population of 66.4% and 24.7%, respectively.
Variants of concern
Against the B.1.1.7 variant, defined by those with a positive B.1.1.7 swab, the vaccine generated a negligible immune response for two weeks following the first dose, though reached 81.6% and 94.4% in weeks three and four. The second dose then induced 99.2% immunity for two weeks, rising to 100% for at least two weeks following.
Similarly, the vaccine generated little immune response for the first two weeks after the first dose against the B.1.351 variant of concern, reaching 47.9% and 73.7% in weeks three and four. However, the second dose of the vaccine caused a rise in effectiveness to 96.4% two weeks or more later.
Both the B.1.1.7 and B.1.351 SARS-CoV-2 variants of concern also saw similar drop-offs in terms of severity of disease or probability of fatality following administration of the vaccines, with low effect in weeks one and two, rising rapidly to 70.3% and 92.1% effectiveness in weeks three and four.
Two or more weeks after the second dose, the effectiveness of the vaccine in limiting disease severity reached 95.7%, with vaccine effectiveness against symptomatic infection (i.e., infected individuals, but with no symptoms) determined to be 98.6%. Further, the vaccine effectiveness against asymptomatic infection, having no infection at all, was calculated to be 92.5%.
The group notes that the development of protection against the B.1.351 variant exhibited a slower rate of accumulation than against the B.1.1.7 variant.
Additionally, the majority of protection is provided following administration of only one dose after sufficient time, which is supported by other studies and suggests that a delayed or absent second dose may be a valid vaccine-sparing strategy.
While this study focussed on the Moderna vaccine, other vaccines have been administered in the country, suggesting lesser immune responses than seen here. This may be due to the one-week more significant delay in administering the first and second doses recommended for the Pfizer vaccine or because this vaccine was available earlier. Thus the elderly will have already received it and would not be included in this study.
This younger population made it more difficult to assess the impact of the vaccine against the variants of concern with regards to lethality, as fewer individuals are likely to experience severe COVID-19.
In any case, these findings suggest that the vaccine maintains good efficacy against the B1.1.7 and B.1.351 variants of concern in all regards, comparable to that observed against wildtype SARS-CoV-2.