The Pfizer-BioNTech vaccine was associated with a 30% lower incidence of COVID-19 infection and hospitalization than the AstraZeneca two-dose immunizations, according to a recent medRxiv* preprint study pending peer review. When Delta was the prevalent strain, the data were consistent for at least six months, indicating that there were no differences in fading immunity between the two vaccinations.

The findings, led by Junqing Xie of the University of Oxford in the United Kingdom, reveal that the Pfizer-BioNTech mRNA COVID-19 vaccines provide more protection against SARS-CoV-2 than AstraZeneca. This may help to encourage mRNA vaccines for boosters as well as vaccine mix-and-matching.

Data collection

Researchers conducted a study using data obtained from the UK BioBank, which involved 500,000 individuals aged between 40 and 69 during the period from 2007 to 2010. The dataset included information on sociodemographic factors, lifestyle choices, and health-related aspects. The focus of the study was on individuals residing in England, as vaccination data for Scotland and Wales were not available at the time. The study included participants who received either a one-dose COVID-19 vaccine between January 11, 2021, and February 28, 2021, or a two-dose vaccine between March 22, 2021, and May 9, 2021.

Among the participants, approximately 70,097 individuals aged 50 years or older received the first dose of the Pfizer-BioNTech vaccine, while a total of 98,551 individuals chose to receive the AstraZeneca COVID-19 vaccine. Additionally, around 67,813 participants received two doses of the Pfizer-BioNTech vaccine, while 89,030 individuals received two doses of the AstraZeneca vaccine.

On average, individuals who received the Pfizer-BioNTech vaccine were slightly older, with an average age of 71.35, compared to those who received the AstraZeneca vaccine, who had an average age of 71.06. The majority of participants in both groups were male and identified as White.

The main differences observed between the vaccination groups were the timing of vaccination and socioeconomic factors such as income. Among the approximately 14,000 individuals who received a single dose of the Pfizer-BioNTech vaccine, 200 individuals later tested positive for COVID-19 infection, resulting in an incidence rate of 13.7 per 1,000 people. Similarly, out of the approximately 20,000 individuals who received a single dose of the AstraZeneca vaccine, 261 individuals tested positive for SARS-CoV-2, yielding an incidence rate of 12.6 per 1,000 people.

However, after further adjustments in the analysis, favoring the Pfizer-BioNTech vaccine (with a hazard ratio of 0.72), it was found to provide greater protection against SARS-CoV-2. The risk of hospitalization was similar for both vaccines, mirroring the risk of infection.

Findings

SARS-CoV-2 was found in approximately 1,361 of the 34,991 patients who got two doses of Pfizer-BioNTech. In comparison, following two doses of the AStraZeneca vaccine, 2,497 patients out of 44,084 tested positive. The Pfizer-BioNTech vaccine was found to be the most effective in preventing infection and hospitalization.

Unadjusted and adjusted HR were almost identical, favouring BNT162b2. The rates of Covid-19 hospitalisation remained low in both cohorts, but higher amongst ChAdOx1 (IR: 4.55 per 1,000 person-years) compared to BNT162b2 recipients (IR: 3.47 per 1,000 person-years), with adjusted HR of 0.71 favouring BNT162b2,” explained the researchers.

Limitations

Several study constraints could have influenced the final results. Differences in testing rates between vaccinated and unvaccinated patients exposed to SARS-CoV-2, for example, could have impacted the observational results.

Participants’ personal information was obtained a decade ago and may have changed since then. Despite the fact that all participants were middle-aged or older, the researchers estimate very minor changes in socioeconomic position and education. Furthermore, unexplained variables could change the link between infection and perhaps understate the comparative vaccine effectiveness.