Effectiveness of COVID-19 vaccines against ICU admission during … – BMC Infectious Diseases

The BA.1 subvariant of Omicron was responsible for the initial Omicron outbreaks around the world. However, BA.1 has been quickly replaced by BA.2 within months, and later by BA.4 and BA.5 (BA.4/5). As of early September 2023, the subvariants of Omicron are circulating, including EG.5, XBB.1.5, and XBB.1.16, and are considered the dominant nationwide. Subsequently, these characteristics of Omicron affect how it spreads and responds to treatments and vaccinations [28,29,30].

In early December 2021, the first case of Omicron was reported in Saudi Arabia with a highly transmissible nature and risk of immune evasion. However, since the beginning of COVID-19 in early March 2020, the government in Saudi Arabia implemented a comprehensive response to prevent the pandemic surge involving travel restrictions, lockdowns of schools and universities, and suspension of attendance, followed by a complete curfew. Moreover, the Umrah was suspended, and the booking of Hajj was restricted to local COVID-19 recovered cases [31,32,33].

We conducted a cohort study including 14,103 individuals with SARS-CoV-2 living in KSA, aiming to estimate the distribution of Omicron variant in different regions of Saudi Arabia and to determine the effectiveness of different types of vaccines with the Omicron variant. In the current study, 59.48% were fully vaccinated (>7days after of two or more doses), 13.12% were partially vaccinated (>14days after first dose through day 7 after second dose), and 27.40% were unvaccinated (days from cohort entry until receipt of first vaccine dose) [26]. Unvaccinated individuals were significantly younger than the vaccinated and partially vaccinated population with p<0.001, as well the largest proportion of the unvaccinated group were non-Saudi with p<0.001.

The high coverage of COVID-19 vaccination among the Saudi population is translated to the effort of the government in implementing a ranged distribution plan for vaccination targeting the largest size of the population of each city, prioritizing cities of high population as the capital Riyadh, followed by Jeddah, Dammam, Madinah, and Makkah. [34].

In the present study, simple and multiple logistic regression is used to study the association between vaccination status and ICU admission while controlling for age and gender. In unvaccinated participants were 2.7 times higher of being admitted to the ICU compared to the fully vaccinated participants. This is in line with a study published recently they found hospitalization rates were 10.5 times higher in unvaccinated persons and 2.5 times higher in vaccinated persons with no booster dose [35]. However, some studies found the protection against Omicron depends on the type of vaccine, in a large cohort research in Singapore involving over 2.5 million people aged 30 or older. These data demonstrate that booster mRNA vaccine protection against severe COVID-19 was persistent over six months independent of vaccine combination, and 3-dose of inactivated vaccine type gave more protection than 2-dose but less protection than 3-dose mRNA [36].

Also, Cox regression is conducted to see the effect of number of doses on ICU admission while adjusted for age and gender. We found that the HR for ICU admission is increased when the age is increased. Similar results have been observed in previous literature they found those under 40years old represent a small proportion of the total number of most severe COVID-19 cases in Europe [37]. Our finding found that there is no difference between males and females in regard to ICU admission. In contrast, an early finding revealed that men are more at risk for a worse outcome [38].

At the same time, the risk of admission to the ICU is decreased with a higher number of doses. This analysis shows that the booster and two doses effectively reduce the risk of ICU admission due to Omicron infection, compared to one dose by 91% and 43%, respectively. This finding is similar to the Qatari study, they found that booster is effective by 76.5% (95% CI, 55.9%-87.5%) against Omicron-related hospitalization and death [16].

We also studied the distribution of the Omicron variant across different regions of Saudi Arabia. The first conducted study for Omicron-infected patients was in a single medical center in Saudi Arabia. This was achieved by AlBahrani et al., showing that the rate of hospitalization (14%) was lower than previously reported in the first and second wave of COVID-19. Nonetheless, the hospitalization rate was inversely correlated with the number of vaccination doses with least admission (5.4%) among fully vaccinated patients. They reported a rate of ICU admission 3.5% and 2% mechanical ventilation rate [1].

In the current study, the vaccination status was significantly different in different regions as the highest proportion of fully vaccinated participants inhabited Tabouk with 71.8% followed by Asir region with 64% then the Eastern region with 62.8% of its population.

Regarding Omicron infection, Al-Madinah Al-Monawarah had the highest number of cases followed by Riyadh region, then Makkah Al-Mokarramah region. It is worth mentioning that during the study period (Jan 2022- Jun 2022), Saudi Arabia has lifted all COVID-19 restrictions on Hajj and Umrah for local and international pilgrims. The announcement was made after the Ministry of Hajj and Umrah released Ramadan 2022 Operational Plan of the two holy mosques [39]. This might explain the highest number of cases, especially in Al-Madinah and Makkah.

The disparity in ICU among regions may include several factors; the literature indicates the association between socio-demographic factors and variations in COVID-19 outcomes. Likewise, many studies have reported the relationship between comorbidities and severe COVID-19 [40,41,42]. For example, the fact that Najran had the highest rate of ICU admission could relate to advanced age and comorbidities such as Type 2 diabetes mellitus (DM2), cardiovascular disease, and obesity, which was discussed previously in a national study [43]. Whereas demographics factors and comorbidities are related to regional variation, other factors, such as disparities in income, access to healthcare resources, education levels, and overall population health, are associated with the COVID-19 outcome in different regions [44,45,46].

One of the limitations in this study is the data was only limited to the samples received by PHA as a part of surveillance. Also, the assessment of differences in behavior or adherence to the COVID-19 precautions are unaccounted among vaccination groups in this study. For example, those who were unvaccinated may be less likely to wear a mask or take precautions. So, this could either lead to overestimation or underestimation. However, this limitation is minimized because of the high willingness and rate of vaccination in Saudi Arabia.

To eliminate confounders, we adjusted for age and sex, but we did not account for other factors that may have influenced the outcomes, such as comorbidity, obesity, smoking and occupation. However, given the studys observational nature, residual confounding remains possible despite adjustment for several potential confounders.

We did not estimate the vaccine's effectiveness against death, symptomatic infections or organ injury because we assessed only patients who have been admitted to ICU.

To the best of our knowledge, this study is the first investigation to analyze and report the effectiveness of two different vaccines against the COVID-19 Omicron variant in Saudi Arabia. Nonetheless, this study includes a large and diverse population from various regions in Saudi Arabia. As the majority of all ages had already received their third doses during Omicron dominant period, it was possible to estimate the effectiveness of two and three doses in the study period.

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Effectiveness of COVID-19 vaccines against ICU admission during ... - BMC Infectious Diseases