In a new study from Kaiser Permanente, researchers found 2 doses of the Moderna COVID-19 vaccine were highly effective against all SARS-CoV-2 variants.
However, vaccine effectiveness against the delta variant moderately declined with increasing time after vaccination.
This study confirmed effectiveness against all variants during the study period, although the team did find a drop in effectiveness over time against delta infection, from 94% effectiveness in the first 2 months after vaccination to 80% effectiveness after 6 months.
Protection against hospitalization due to the delta variant remained high at 98% effectiveness.
This study included 8,153 people who tested positive for SARS-CoV-2, with specimens collected from March 1 to July 27, 2021.
Among them, 91.3% were unvaccinated, 1.4% had received 1 dose of Moderna COVID-19 vaccine, and 7.3% had received 2 doses of the Moderna COVID-19 vaccine.
Variants were identified for 5,186 of those samples; 39.4% were delta, 27.7% alpha, 11.4% epsilon, 6.9% gamma, 2.2% iota, 1.4% mu, and 11.1% other variants.
At the time of this study, the omicron variant had not yet been detected in the Southern California region.
The researchers compared people who tested positive with those who tested negative.
They found:
The 2-dose Moderna COVID-19 vaccine effectiveness against infection by variant: Delta: 86.7%; Mu: 90.4%; Alpha: 98.4%; Other identified variants: 96 to 98%.
People who received the 2-dose Moderna COVID-19 vaccine were strongly protected against COVID-19 hospitalization associated with the delta variant:
Vaccine effectiveness against delta hospitalization was high at 97.5%;
Vaccine effectiveness against hospitalization for non-delta variants was not estimated because there were no hospitalizations with non-delta variants identified among vaccinated people;
Among people who had received the 2-dose Moderna COVID-19 vaccine, no hospitalized deaths occurred; and
The vaccine effectiveness of 2 doses of Moderna COVID-19 vaccine against delta infection was 87.9% among people ages 18 to 64, and 75.2% among people ages 65 and older.
The team says this study provides reassuring evidence of the effectiveness of 2 doses of Moderna COVID-19 vaccine in preventing COVID-19 infection and hospitalization due to variants including delta.
But the findings of moderately reduced vaccine effectiveness of Moderna COVID-19 vaccine overtime against delta infection supports current booster dose recommendations.
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The study is published in The British Medical Journal. One author of the study is Katia Bruxvoort, Ph.D.
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