Delta Variant Lowers mRNA COVID-19 Vaccine Effectiveness

Eurosurveillance published observational data regarding mRNA COVID-19 vaccine effectiveness (VE) against the Delta (B1617.2) coronavirus variant on September 2, 2021. This study found mRNA COVID-19 vaccine VE was about 65% in Norway during August 2021.

The Comirnaty and SpikeVax VE against infection were lower for the Delta variant than the Alpha variant among partly and fully vaccinated individuals.

Nevertheless, fully vaccinated individuals (2-doses) had a lower risk of infection with the Delta (HR 0.35 (95% CI: 0.32–0.39)) and Alpha variant (HR 0.16 (0.13–0.18)) compared to unvaccinated individuals.

This finding is in line with previous studies that assessed VE against symptomatic infections, said these researchers.

However, these researchers stated, 'Our estimates of VE should be interpreted with caution since they are based on observational data.'

'In addition, comparisons with other studies should take into account different study designs, e.g., in our study, we included both symptomatic and asymptomatic infections.'

'Effectiveness of COVID-19 vaccines against SARS-CoV-2 infection with both the Delta and Alpha variants appears to be considerable among fully vaccinated people in Norway,' concluded these researchers.

In Norway, the Delta variant was first identified in April 2021 and accounted for 67% of all sequenced samples by July, overtaking the Alpha variant (B.1.1.7) as the dominating variant.

As of September 4, 2021, about 69% of adults in the EU/EEA were fully vaccinated against COVID-19.

Note: No specific funding was received. The study was performed as part of routine work at the Norwegian Institute of Public Health. No researcher conflicts of interest were disclosed. Eurosurveillance is published by the European Centre for Disease Prevention and Control, located in Stockholm, Sweden.