The rapid development and rolling out of vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been considered as a huge step forward towards containing the ongoing coronavirus disease 2019 (COVID-19) pandemic.
However, the continual emergence of SARS-CoV-2 variants across the world has made the scientific community skeptical towards the effectiveness of the available vaccines. Additionally, some of the variants have been deemed as variants of concern (VOC) owing to their high infectiousness, virulence, and immunity evasion potential.
SARS-CoV-2 Delta variant and vaccines
One of the VOCs that has been particularly troubling is the Delta variant (or the lineage B.1.617.2), which was first reported in India in late 2020. This variant has shown a high transmission rate and is associated with the massive COVID-19 second wave recently experienced in India. The Delta variant was later found to have rapidly spread in more than 92 countries and is currently known to be the largest circulating SARS-CoV-2 strain in the world.
To date, several vaccines have received emergency use authorization (EUA) from various regulatory bodies and are being used to vaccinate millions of individuals worldwide. However, these vaccines have been developed against the original novel SARS-CoV-2 strain that was first reported in Wuhan, China, in 2019.
Hence, it is imperative to constantly evaluate the efficacy of these vaccines against the newly emerging variants, such that the vaccine developers can modify the vaccine designs as and when required. In vitro studies had shown a decreasing neutralizing efficacy of vaccines such as Pfizer-BioNTech vaccine (BNT162b2) and the Oxford-AstraZeneca vaccine (ChAdOx1) against the Delta variant.
Effectiveness of COVISHIELD and COVAXIN vaccines against the Delta variant
A new study has been published on the medRxiv* preprint server that has evaluated the clinical outcomes of the COVID-19 patients hospitalized in AIG hospitals, Hyderabad, India, between April 24, 2021, and May 31, 2021. These hospitalized patients were vaccinated with either COVISHIELD (ChAdOx1, Serum Institute of India) or COVAXIN (BBV-152, Bharat Biotech). During this time, the second massive COVID-19 wave prevailed in India, with the dominant circulating strain being the Delta variant. The clinical outcomes of the vaccinated patients were compared with the unvaccinated COVID-19 patients admitted to hospitals.
During the study period, a total of 1,161 COVID-19 patients were admitted into AIG Hospitals. Among these, 495 individuals were vaccinated, and the remaining patients were unvaccinated. The researchers found that for both the hospitalized groups (i.e., vaccinated and the unvaccinated), the mean age was of 58.50 ± 13.10 years. Among the vaccinated group, 251 individuals received COVISHIELD, where 168 people took a single dose, and 83 completed both the vaccine doses.
Similarly, among the 203 people who received COVAXIN, 99 took the first dose, and 104 received both doses. The vaccine type or the number of doses was not clear for the remaining 41 candidates.
The study authors found that the individuals infected with SARS-CoV-2, belonging to the vaccinated group, had significantly more comorbidities such as diabetes, hypertension, and cardiovascular disease, than the unvaccinated group.
The study also revealed that vaccinated individuals have significantly higher neutralizing antibodies and lower inflammatory markers such as serum ferritin and lactate dehydrogenase than the unvaccinated group. The lower inflammatory markers in the vaccinated group may be owing to early neutralization of the virus that prevented aberrant inflammatory response.
The study authors observed a trend – namely, increasing antibody levels and decreasing inflammatory markers in individuals who received two doses of the vaccines. However, such a trend was not found in individuals who received a single vaccine dose. In the unvaccinated group, researchers found higher IgM in antibody titers suggesting that these individuals were severely infected by the virus.
The severity of the COVID-19 disease was noted in terms of ICU admission and the requirement of ventilator support. In this study, the vaccinated group revealed significantly low severity when compared with the unvaccinated group. However, no significant difference was observed with respect to the incidence of acute kidney injury (AKI), or thrombotic complications, or requirement for renal replacement therapy (RRT) between the studied groups.
The mortality rate was lower by 50% in the fully vaccinated group with COVID-19 infections, when compared with the unvaccinated group with the SARS-CoV-2 infection and the group of individuals who received a single dose of a vaccine and were infected with the virus. The authors of this study revealed that the majority of the deceased, who were completely or partially vaccinated, showed a minimal or negative immune response to the vaccine. Hence, new strategies must be implemented, such as additional booster doses or change of vaccine type, for the individuals who did not show any response to vaccination.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.