A Bahrain study comparing COVID-19 vaccines has found that vaccination is highly effective in preventing hospitalisation and death, but the Chinese Sinopharm jab may be less effective than Pfizer-BoinTech for people over the age of 50.
A preprint published on the study noted a higher risk of infections, hospitalisations, ICU admissions and deaths among people over 50 who had received Sinopharm compared to those in the same age group who had received Pfizer-BioNTech.
“… The percentage of deaths among all PCR positive post-vaccination COVID-19 cases among recipients of the Sinopharm vaccine was 0.46% (i.e, 112 deaths) versus 0.15% for Pfizer-BioNTech (i.e., three deaths) and 0.03% for AZ/Covishield (one death). This trend was consistent for all COVID-19 events, i.e., infection, hospitalisation, ICU admission and death,” the authors wrote.
The study, which has yet to be peer-reviewed, compared four different vaccines rolled out in Bahrain; namely, Sinopharm, Pfizer, AstraZeneca and Sputnik V.
Sinopharm is the most widely used COVID-19 vaccine in countries like Bahrain and Sri Lanka, and the researchers acknowledged a possible skewing in the data due to oversampling and due to testing close contacts who were at higher risk of infection. However, given what they called the “highly significant” differences in post-vaccination infection rates between Sinopharm recipients and Pfizer recepients, particularly in the 0ver-50 demographic, it was “unlikely that these confounding factors could explain the difference in outcomes between the two vaccines.”
The team of researchers that included experts from Colombia University, New York, concluded that the four vaccines were indeed effective in reducing infections, hospitalisations, ICU admissions and deaths in vaccinated people compared to those unvaccinated, prior to, and during the period when the highly infectious delta variant of SARS-CoV-2, the virus that causes COVID-19, became dominant in Bahrain in May 2021.
“However, after censoring early vaccine recipients of Sinopharm vaccine, compared to Pfizer-BioNTech recipients, individuals vaccinated with Sinopharm had a higher risk of post-vaccination infections, hospitalisations, ICU admissions and deaths, especially in those > 50 years old.
“Our overall findings support the value of vaccination in preventing COVID-19 related events even with the advent of the delta variant. These data support the urgent need to expand vaccination access around the world, and may serve to guide the choice of vaccines in the context of the delta variant,” the authors wrote in the preprint’s abstract.
In order to limit multiple comparisons, the authors carried out paired testing among five groups: unvaccinated vs Sinopharm, unvaccinated vs Pfizer, unvaccinated vs AstraZeneca (AZ)/Covishield, and unvaccinated vs Sputnik V.
Using pair-wise comparisons between unvaccinated individuals (over 50 and younger than 50), the researchers found a significantly higher percentage of hospitalisation, ICU admissions and deaths in the unvaccinated group compared to the vaccinated group for all four vaccines.
“For instance, the percent of deaths among all COVID-19 cases in unvaccinated people over 50 years of age was 3.8-fold higher compared to Sinopharm, and approximately 7.5-fold higher than the Sputnik V vaccine recipients. There were no deaths reported in the AZ/Covishield vaccinated group. In patients younger than 50 years, the percent of death among all COVID-19 cases in unvaccinated people were 8.1-fold higher compared to Sinopharm vaccine recipients. There were no deaths reported in this age cohort in Sputnik V and Pfizer-BioNTech vaccine recipients, and one death among the AZ/Covishield vaccine recipients,” the preprint said.
However, despite the overall effectiveness of all four vaccines in decreasing risk of COVID-19 related hospitalisations, intensive care unit admissions and deaths when compared to unvaccinated individuals, the researchers said their initial analysis showed a higher risk of COVID-19 infection and clinical escalation among those who received Sinopharm compared to those who got other vaccines.
To avoid multiple comparisons among the five groups, the team had used the data for Pfizer as the comparator and found that that vaccine was associated with statistically significantly lower rates of post-vaccination COVID-19 infections, hospitalisations, ICU admissions and deaths compared to Sinopharm among those over 50.
“This was also noted for those under 50 years of age, although the difference in the death rates in this cohort was not statistically significant; this may have been due to low numbers of events (hospitalisations, etc),” the team said.
Acknowledging the study’s limitations, the researchers said limited information on socioeconomic and clinical characteristics of the individuals included in the analyses hindered the ability to take into account any adverse selection that might have occurred due to geographic access and clinical characteristics and their effects on the uptake of different vaccines.
“Similarly, we recognise that evolution of the adoption of pandemic protective measures changed over time, which may have influenced risk for SARS-CoV-2 infection. In particular, we note that Sinopharm was the only vaccine used early in the pandemic when knowledge of diagnosis and management of cases of COVID-19 was evolving; however, we censored early recipients of the Sinopharm vaccine to mitigate any bias caused by this early cohort of recipients.
“Since the Sinopharm vaccine was deployed at an approximately three-fold higher rate compared to the Pfizer-BioNTech vaccine, we cannot rule out a skew in the data due to oversampling of individuals who received the Sinopharm vaccine and experienced infections, hospitalisations, ICU admissions and deaths. Additionally, it is important to note that testing efforts included close contact of cases of COVID-19, which may have selected a group at higher risk for infection,” they said.
However, as noted earlier, the disparity between Sinopharm and Pfizer in terms of hospitalisation and deaths in the over-50 category are not explained by such factors, the researchers noted.
“We conclude that COVID-19 vaccination is an effective strategy at mitigating the risk for SARS-CoV-2 and its consequences, especially among individuals older than 50 years of age. However, in a pairwise comparison, the performance of the Pfizer-BioNTech vaccine was superior to the Sinopharm vaccine, especially in older individuals and in the context of the emergence of the delta variant,” it said.
According to Nature, a recent study in the UK has found that although Pfizer-BioNTech and Oxford-AstraZeneca COVID-19 vaccines are effective against delta, their protection drops away over time.
Citing a preprint by researchers at the University of Oxford, Nature reported that Pfizer was 92% effective at keeping people from developing a high viral load — a high concentration of the virus in their test samples — 14 days after the second dose. But the vaccine’s effectiveness fell to 90%, 85% and 78% after 30, 60 and 90 days, respectively.
AstraZeneca, meanwhile, was 69% effective against a high viral load 14 days after the second dose, falling to 61% by 90 days.
However, the drop in effectiveness shouldn’t be cause for alarm, Nature reported quoting Sarah Walker, a medical statistician at the University of Oxford who led the study. For “both of these vaccines, two doses are still doing really well against Delta”, she was quoted as saying.