MRNA shots effective against COVID-19 Delta variant

Immunizations with mRNA-based vaccines are strongly effective against symptomatic and severe COVID-19 disease associated with the virus’ Delta variant, according to a recent Singapore study.

 “Vaccinated individuals had a more rapid viral load decline, which has implications on secondary transmission and public health policy. Rapid and widespread implementation of vaccination programs remains a key strategy for control of COVID-19 pandemic,” the researchers said.

The multicentre, retrospective cohort analysis included 218 COVID-19 patients who were confirmed to have been infected with the virus’ Delta variant. Of the participants, 84 had been given mRNA vaccines, of whom 71 had already completed the dosing course. Four were give non-mRNA shots, while 130 were unvaccinated at the time of infection. [Clin Microbiol Infect 2022;28:612-e1-612.e7]

Analysis of baseline biomarkers showed that unvaccinated participants had significantly worse levels of lymphocyte count, C-reactive protein, lactate dehydrogenase, and alanine aminotransferase—all known indicators of poor COVID-19 outcomes. Likewise, pneumonia was more common in the unvaccinated group, which also showed a greater need for supplemental oxygen and intensive care admission.

Broader comparisons similarly showed that the clinical presentation and course of COVID-19 was better in those who had received even one vaccine dose.

These findings were compared in multivariate logistic regression modelling, which found that vaccination reduced the likelihood of severe COVID-19, defined as the need for supplemental oxygen, by more than 99 percent (adjusted odds ratio [OR], 0.073, 95 percent confidence interval [CI], 0.016­­–0.343; p=0.001). A similar effect was reported for those who had received only one dose at the time of infection.

Moderately severe COVID-19, defined as the development of pneumonia, was likewise significantly reduced by vaccination (adjusted OR, 0.069, 95 percent CI, 0.027­–0.180).

Serological assessments further revealed that 100 percent of vaccinated patients produced detectable levels of antispike protein antibodies within a week of Delta infection, as opposed to only 16 percent of their unvaccinated counterparts. Antinucleocapsid seroconversion did not differ between groups.

Virological kinetics showed similar trends. While the overall viral load, expressed as serial cycle threshold (Ct) values, were comparable between vaccinated and unvaccinated patients (19.2 vs 18.8; p=0.929), those in the former subgroup showed a significantly faster rate of Ct over time, indicative of a quicker decline in viral load (p<0.05).

“In contrast to existing studies that showed lower viral load in vaccinated patients, initial viral load indicated by polymerase chain reaction Ct values was similar between vaccinated and unvaccinated patients with B.1.617.2,” the researchers said. “Nevertheless, in our study, vaccinated patients appeared to clear viral load at a faster rate.” [N Engl J Med 2021;385:320-329]

“Further studies should elucidate immunological features driving vaccine breakthrough infection to improve vaccine-induced protection,” they added.