A study of the Oxford/AstraZeneca CCP virus vaccine trials published in the Lancet has raised questions around the vaccine’s higher efficacy rate reported last month.
The peer-reviewed study of the data from four trials of the vaccine, published on Dec. 8, indicates further evaluation is needed as older people were not included in the small sub-group study that showed a higher efficacy rate of 90 percent for the vaccine. There was also uncertainty surrounding the results.
The main study results showed an efficacy of 62 percent.
Oxford/AstraZeneca said that participants receiving one half-dose of the vaccine followed by a full dose, as opposed to two full doses given to most participants, displayed a higher rate of efficacy. The interim data, which was published in November, was seen as welcome breakthrough in the search for a vaccine to combat the spread of the CCP (Chinese Communist Party) virus.
However, following the Lancet study publication, experts have said the data presents a dilemma to regulators, because the dosing regimen giving the higher efficacy rate has not been tested in older people—the ones who would benefit the most from the vaccine. And only 12 percent of participants in the main group were over 55.
“The report on the successful trial of the Oxford/AstraZeneca [vaccine] presents regulators with something of a dilemma. Data are most compelling for the cohort who got half a dose of the vaccine in their first jab,” Simon Clarke, an associate professor in cellular microbiology at the University of Reading, said in a statement.
“Unfortunately, this cohort was relatively small, reducing the reliability of the findings—moreover it did not contain any older participants (age 55 or over) and it remains possible that if the regulators allowed the vaccine to be used in this manner, the most at risk group may not be protected.”
The vaccine, which has yet to be reviewed by the Medicines and Healthcare products Regulatory Agency (MHRA), is, however, seen by some to be still useful, despite the lower efficacy rate.
“This confirms the previously-released findings, namely that safety and effectiveness of this Oxford COVID-19 vaccine candidate are overall very good. It is possible that we will see this vaccine reviewed quite soon by the MHRA, and thus there may be the option of two available vaccines in the near future,” Michael Head, a senior research fellow in global health at the University of Southampton, said in a statement.
However, acknowledging that different approaches may be needed to treat the over 70s, he added, “The researchers were not yet able to fully assess how effective this vaccine is in elderly populations, so we are likely to see a continuation in the use of the Pfizer vaccine in older people.”
The trials are yet to be completed and more data is expected for older people.
Some experts additionally expressed concerns over the reliability of the results from the group showing 90 percent efficacy, with the paper stating “there is a possibility that chance might play a part” in the results. This could mean the full-dose regimen showing only 62 percent efficacy could gain approval from the regulators but not the half-dose/full-dose regimen.
“A lower vaccine efficacy does run the risk of leaving a large proportion potentially unprotected despite being vaccinated,” Julian Tang, a clinical virologist and honorary associate professor in respiratory sciences at the University of Leicester, said in a statement.
“Those who have been vaccinated and think they are immune may behave more freely which may serve to spread the virus further if they do become infected.”
In November, the MHRA announced it would be accelerating its review process of the Oxford/AstraZeneca vaccine.