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.
"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."