Efficacy of BBIBP-CorV vaccine against severe consequences of COVID-19 in Abu Dhabi, United Arab Emirates

This study provides estimates of the efficacy of the inactivated vaccine BBIBP-CorV (Sinopharm) for the prevention of hospitalizations, intensive care unit admissions and deaths related to COVID-19 in a large population of the Emirate of Abu Dhabi. Our study found that two doses of inactivated BBIBP-CorV vaccine were 79.6%, 86%, and 84.1% effective in preventing COVID-19-related hospitalization, ICU admission, and death, respectively. . Efficacy against ICU admissions and deaths was lower in our study compared to a recently published UAE study of the BBIBP-CorV vaccine, which included a smaller sample size and shorter follow-up duration. In addition, the inclusion of only patients infected with COVID-19 may have overestimated the effectiveness of the vaccine.14.

Our results showed lower efficacy than those reported in the secondary analysis of the phase III trial, which showed 100% efficacy against severe cases of COVID-19, which included a composite of severe cases and deaths .8. This could be because our study represents real-world data, including high-risk populations, with a longer follow-up period, compared to the median follow-up of 77 days in the phase III trial. The emergence of concerning new variants of the SARS-CoV-2 virus during this study period, which have been shown to evade vaccine-induced antibodies, may also have contributed to the lower efficacy.17.

Using the Cox proportional hazard model with interaction terms, we analyzed efficacy by age group, gender, comorbidities, ethnicity, and month of observation. We found that vaccine effectiveness against hospitalization decreased with age, as confirmed by reduced vaccine protection in the older age group (≥60 years), compared to the younger study population. These findings are supported by other studies, which have reported an inverse relationship between COVID-19 vaccine efficacy and age.18,19,20. The efficacy of our reported vaccine against hospitalization in the older age group is likely to be underestimated, as UAE regulations required hospitalization of all patients over 65 with a RT-qPCR (Reverse Transcription Quantitative real-time PCR) test positive for SARS-CoV-2, regardless of vaccination status as a proactive measure to prevent serious complications in this vulnerable population21. Given that 40% of hospitalizations in our study occurred in patients aged ≥ 60 years, this result should be interpreted with caution. The difference between the two age groups in terms of vaccine effectiveness against ICU admission and death was not statistically significant.

Regarding gender, our study showed that the vaccine is more effective in preventing hospitalization in women (82.3%), compared to men (74.5%), which is supported by another inactivated CoronaVac vaccine study22. Yet men were more protected against admission to intensive care. No significant gender differences in mortality were found.

While numerous studies have reported reduced vaccine efficacy in people with comorbidities17.20, our study found increased vaccine efficacy against hospitalization, ICU admission, and death in people with comorbidities, compared to those without comorbidities. This could be explained by the high risk of hospitalization in unvaccinated people with comorbidities, compared to the significantly lower risk in unvaccinated people without comorbidities. As such, there was a greater post-vaccination risk reduction in people with comorbidities compared to those without comorbidities, and therefore increased vaccine efficacy, in the population with comorbidities.

There were fewer deaths in our population, compared to other studies. This may be due to the proactive measures taken in Abu Dhabi, including hospitalization of all high-risk patients, regardless of symptom severity or health insurance status. Additionally, all patients infected with COVID-19 received standardized treatment in dedicated COVID-19 hospitals.

Of note, vaccine efficacy against all COVID-19 outcomes was high during the months of October through December 2020, likely because the rollout of emergency use authorization vaccination for frontline workers in the UAE began in September 2020, and this period preceded the emergence and circulation of variants of concern9. As vaccine efficacy was measured at three-month intervals to monitor for waning efficacy over time, the reduction in vaccine efficacy during the months of January to June 2021 is likely due to the emergence new variants of the SARS-CoV-2 virus, some with increased transmissibility, infectivity, morbidity and mortality17.22. During this period, alpha and delta variants of SARS-CoV-2 were the most prevalent circulating strains in the UAE23.24.

Twelve-month follow-up revealed that vaccine effectiveness began to decline after three months and effectiveness against ICU admissions fell below 75% after six months. Similar results were reported in another study which observed that the long-term efficacy of the BBIBP-CorV vaccine decreased from 88% to 64% within six months.15. Other studies have also demonstrated a progressive decrease in immune response and vaccine efficacy within months of vaccination with the BNT162b2 vaccine.12,16,25. This decline in efficacy over time is likely explained by viral evasion of the vaccine-induced immune response through antigenic changes in new variants of the SARS-CoV-2 virus, as well as declining levels antibody response from studies that showed a reduction in anti-S antibodies three weeks after the second dose of vaccination26. These results provide a good rationale for administering booster doses to prevent severe consequences of COVID-19, although the primary vaccine series still appears to be effective in reducing mortality.

Our studies have many strengths. First, the study included a large, comprehensive dataset, which covers the entire population of Abu Dhabi, the largest emirate in the United Arab Emirates. Second, data were matched for age, sex, comorbidities, ethnicity, and month of observation, to standardize the comparison and avoid potential confounders. Third, the data we used provided a long follow-up period reaching nearly 12 months. These allowed us to estimate, with great precision, the overall efficacy, the efficacy on different risk factors and the decline in efficacy over time. Additionally, we measured vaccine effectiveness at three-month intervals (October-December 2020, January-April 2021, and May-July 2021). In each interval, participants were followed for a maximum of three months. This allowed us to monitor the decline in efficiency over time and to study the impact of variants of concern on efficiency. This was possible because each three-month interval corresponded to specific predominant variants (wild-type virus was predominant in October-December 2020, alpha variant was predominant in January-April 2021, and delta was predominant in May-July 2021) [Unpublished data for the Abu Dhabi Public Health Center, Department of Health, Abu Dhabi, UAE].

Limitations of our study include examining only hospitalization, ICU admission, and death as outcomes. We did not estimate vaccine effectiveness against other outcomes, such as symptomatic infections or organ damage. Additionally, we adjusted for factors such as age, gender, ethnicity, comorbidities, and month of study entry, but did not control for other factors that may affect the study. have influenced outcomes such as obesity, smoking and occupation. Another limitation of our study is that although the decline in vaccine efficacy over time was analyzed, we could not rule out the effect of changes in circulating variants on the decline in vaccine efficacy. Over the month. Finally, we have not included infections due to COVID-19 among the results, mainly because the United Arab Emirates has one of the highest per capita testing programs for COVID-19 in the world. For public health relevance, we primarily studied severe, hospitalized cases of COVID-19, which are a better indicator of vaccine effectiveness.

We would like to conclude that the BBIBP-CorV inactivated vaccine (Sinopharm) was effective in preventing and reducing COVID-19-related hospitalizations and ICU admissions, as well as mortality. These results also provide insight into the impact of risk factors on vaccine efficacy. Our data further support the need for booster doses to increase protection against severe consequences of COVID-19 and underscore the need for continued monitoring of vaccine effectiveness over time to inform policy.

Sara H. Byrd