The AstraZeneca vaccine has been found to be mostly effective against the United Kingdom variant of the CCP virus, according to preliminary data published on Feb. 4.
The B.1.1.7 variant has been responsible for most CCP virus cases in the United Kingdom after it first emerged in the country last November. The variant has also been detected in the United States.
“Data from our trials of the ChAdOx1 vaccine in the United Kingdom indicate that the vaccine not only protects against the original pandemic virus but also protects against the novel variant, B.1.1.7, which caused the surge in disease from the end of 2020 across the UK,” Andrew Pollard, professor of pediatric infection and immunity and chief investigator of the Oxford vaccine trial, said in a statement.
Oxford University is a co-developer of the AstraZeneca vaccine, which uses a modified chimpanzee common cold virus (adenovirus) to instruct the cells inside the body to produce the CCP (Chinese Communist Party) virus spike protein, activating an immune response.
The study (pdf), which hasn’t been peer-reviewed, found the vaccine provided 74.6 percent protection against symptomatic COVID-19 from the B.1.1.7 variant, and 84 percent protection against symptomatic disease from non-B.1.1.7 variants.
However, the “overall efficacy against the B.1.1.7 variant from all cases [symptomatic and asymptomatic or unknown infections] was 66.5 percent.”
Researchers examined genetic sequencing from 323 nasal or throat swabs of 256 participants who tested positive for COVID-19 after receiving a vaccine, in an ongoing phase 2/3 trial. But findings were based only on 120 of the 256 participants.
Sequencing allowed researchers to identify the participants who were infected with the B.1.1.7 variant versus those who were not.
The study also claimed that the AstraZeneca vaccine “results in a reduction in the duration of shedding and viral load.”
This may be the first study on vaccine efficacy against virus variants to discuss cycle thresholds of PCR tests used to diagnose COVID-19.
A cycle threshold value is the number of cycles it takes for the test machine to detect the virus’s genetic material, providing information on whether an individual is infectious or not. “Low PCR Ct [cycle threshold] values are associated with higher viral load,” meaning the individual is more infectious.
The study initially collected over 1,500 throat or nasal swabs from 499 participants who tested positive for COVID-19, but only 323 of the swabs could be sequenced from 256 individuals.
One of the reasons a smaller number of swabs was sequenced may be due to laboratories not sequencing samples with high cycle thresholds. “Samples with a high Ct value (>30) were not routinely sequenced by several COG UK laboratories, thus limiting our ability to assess the lineage of low viral load specimens, which were overrepresented in asymptomatic participants,” the study states.
Reasons were not given as to why these laboratories didn’t sequence samples with threshold values higher than 30 cycles.
The researchers said their findings on asymptomatic carriers were consistent with other studies, and that they are not a significant source of transmission.
“In our study, individuals who did not report symptoms had lower viral loads than symptomatic individuals and were NAAT [nucleic acid amplification test] positive for a shorter period of time. This is consistent with published data that asymptomatic individuals may be responsible for fewer secondary transmissions than symptomatic individuals,” they said.
The researchers also added that “studies using different PCR platforms have shown that infectious virus was not isolated from patients with a Ct value greater than 24.”
