Pfizer/BioNTech, Moderna COVID vaccines effective against Delta variant

The mRNA vaccines, such as Moderna and Pfizer/BioNTech, perform well at preventing symptomatic and severe COVID-19 related to B.1.617.2 infection (Delta), a Singapore study has shown. Vaccination leads to a faster decline in viral RNA load and a robust serological response and remains a vital approach in containing the pandemic.

“Highly effective vaccines against SARS-CoV-2 have been developed but variants of concerns (VOCs) with mutations in the spike protein are worrisome, especially Delta which has rapidly spread across the world,” the authors said.

A multicentre retrospective cohort study was undertaken on patients who had received a licensed mRNA vaccine and been admitted to hospitals with Delta SARS-CoV-2 infection. The authors then compared the clinical features, virological and serological kinetics (antinucleocapsid, antispike, and surrogate virus neutralization titres) between fully vaccinated and unvaccinated individuals.

A total of 218 patients were infected with the Delta variant, of whom 84 had received an mRNA vaccine (71 fully vaccinated), 130 were unvaccinated, and four received a non-mRNA vaccine.

Patients in the vaccine breakthrough group were significant older, but their chance of progressing to severe COVID-19 requiring oxygen supplementation was significantly lower following vaccination (adjusted odds ratio, 0.07, 95 percent confidence interval, 0.015–0.335; p=0.001).

Of note, PCR threshold values were similar between vaccinated and unvaccinated patients at diagnosis, but viral loads decreased faster among those vaccinated.

“In addition, [e]arly, robust boosting of antispike protein antibodies was observed in vaccinated patients, [but] these titres were significantly lower against B.1.617.2 as compared with the wildtype vaccine strain,” the authors said.

This study is a preprint and has not been peer-reviewed yet.