Moderna COVID-19 vaccine effective against virus variants, delta protection diminishes over time – archyde

According to a study published in, two doses of the Moderna COVID-19 vaccine were highly effective against all SARS-CoV-2 variants Das British Medical Journal. However, the effectiveness of the vaccine against the Delta variant decreased slightly over time after vaccination.

“While this study provides reassuring evidence of the effectiveness of 2 doses of the Moderna-COVID-19 vaccine in preventing COVID-19 infection and hospitalization for variants including Delta, it also has implications for the booster,” Hung said Fu Tseng, PhD, researcher with the Kaiser Permanente Southern California Department of Research & Evaluation, in a press release. “The results of a moderately reduced vaccine effectiveness of the Moderna-COVID-19 vaccine against the Delta infection over time support the current recommendations for booster vaccination.”

To conduct the study, investigators collected positive SARS-CoV-2 samples from symptomatic and asymptomatic patients for entire genome sequencing. Samples were taken from a total of 8153 people from March 1 to July 27, 2021.

Of these people, 91.3% were unvaccinated, 1.4 had received a single dose of Moderna’s COVID-19 vaccine, and 7.3% received 2 doses of the vaccine. Variants were identified in 5186 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 . The Omicron variant had not yet been detected in the Southern California region at the time of the study.

Investigators compared samples from people who tested positive with those from people who tested negative. They found that the 2-dose vaccination had an effectiveness of 86.7% against the Delta variant, 90.4% against Mu, 98.4% against Alpha, and between 96% and 98% for other identified variants.

In addition, people who received the 2-dose Moderna vaccine were strongly protected against hospitalization, with 97.5% effectiveness against delta hospitalization, and no hospitalizations reported in those with other variants. There were no hospital deaths in patients who received the 2-dose vaccine.

“We did an earlier study that showed the high effectiveness of the 2-dose Moderna COVID-19 vaccine, but when the Delta variant prevailed in early summer 2021, questions arose about its effectiveness against variants,” said Katia Bruxvoort, PhD, Adjunct Investigator with the Kaiser Permanente Southern California Department of Research & Evaluation, in the press release. This study confirmed effectiveness against all variants during the study period, although we did see a decrease in effectiveness against Delta infection over time, from 94% effectiveness in the first 2 months after vaccination to 80% effectiveness after 6 months. The protection against hospital stays due to the Delta variant remained high with an effectiveness of 98%. “


Moderna COVID-19 vaccine effective against virus variants [news release]. Kaiser Permanente; December 15, 2021. Accessed December 15, 2021.

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