Effectiveness of inactivated COVID-19 vaccines against SARS-CoV-2 infections among healthcare personnel in Pakistan: a test-negative, case-control study

Abstract

Objective: During the COVID-19 pandemic, several vaccines that were efficacious in randomized controlled trials (RCTs) were authorized for mass vaccination. In developing countries, inactivated vaccines were widely administered. While inactivated vaccines have been deemed effective in reducing disease severity, for healthcare personnel (HCPs), effectiveness against COVID-19 infections is also essential to reduce the risk to vulnerable patients and ensure a stable healthcare workforce. In addition, there are limited studies examining effectiveness of inactivated vaccines against emerging SARS-CoV-2 variants in real-world settings. We aimed to estimate the effectiveness of inactivated vaccines (BBIBP-CorV and CoronaVac) against RT-PCR-confirmed COVID-19 infections among HCPs in the setting of emerging SARS-CoV-2 variants in Pakistan. Design, setting and participants: A retrospective matched test-negative case-control analysis of existing data of HCPs at a private healthcare system in Pakistan. Methods: HCPs tested between April 1 and September 30, 2021, were included. Each case was matched to two to six controls by the date of the RT-PCR test (± 7 days) to reduce bias. We compared demographics, reasons for testing, and vaccination status between cases and controls using chi-square for categorical variables and t-test for continuous-level data. The odds of getting a PCR-confirmed SARS-COV-2 infection were calculated using conditional logistic regression, after adjusting for age, gender, and work area. Vaccine effectiveness (VE) was calculated as percent VE using (1-OR)*100. Results: Inactivated vaccines were ineffective against COVID-19 infections ≥ 14 days after receiving the first dose [VE: 20% (95% CI: -10, 41; p=0.162)]. The vaccines showed modest effectiveness ≥ 14 days after the second dose against COVID-19 infections [VE: 33% (95% CI: 11, 50; p=0.006)], and symptomatic COVID-19 infections [VE: 36% (95% CI: 10, 54; p=0.009)]. Conclusions: Inactivated vaccines show modest effectiveness against COVID-19 infections in the setting of emerging VOCs. This builds a strong case for boosters and/or additional vaccination.

Exploring the relationship between SARS‐CoV‐2 variants, illness severity at presentation, in‐hospital mortality and COVID‐19 vaccination in a low middle‐income country: A retrospective cross‐sectional study

“…However, we provide valuable clinical evidence regarding the factors associated with disease severity and mortality, specifically in the context of VOC and protective effect of vaccinations. The protective effect observed aligns with the efficacy studies of different vaccines used in Pakistan, which have shown inactivated type of vaccinations were moderately effective against symptomatic COVID-19 20,35.…”

Shift in SARS-CoV-2 variants of concern from Delta to Omicron was associated with reduced hospitalizations, increased risk of breakthrough infections but lesser disease severity

“…As the majority of individuals in our cohort had received inactivated vaccines, it is not surprising that most of the breakthrough infections we observed were from participants who received inactivated vaccines. A systematic review and meta-analysis of 28 studies showed that inactivated vaccines reduced ICU admission and death [46] but have low to moderate effectiveness in preventing symptomatic diseases, particularly from emerging SARS-CoV-2 VOC [13] , [47] . However, it is shown that all vaccination types are effective against symptomatic COVID-19 [13] .…”