Moderna’s COVID-19 vaccine resulted in antibody activity against variants, including the highly transmissible delta variant, six months after the second dose, a study found. However, antibody levels waned over time, and researchers said the results inform the potential need for a booster shot.
“Binding and functional antibodies against variants persisted in most subjects, albeit at low levels, for 6-months after the primary series of the mRNA-1273 vaccine,” study authors wrote.
The study, led by the National Institutes of Health, was published in the Science journal late Thursday, drawing from an analysis of blood samples from 24 participants across several age groups (18-55, 55-70, and 71+), finding that 96% of samples neutralized the delta variant. However, neutralizing activity was lowest against the B.1.351 variant first detected in South Africa, with 54% of samples neutralizing the variant, or a 1.5-fold reduction and 3-fold reduction, respectively.
“We are pleased with these new data showing that people vaccinated with two doses of the Moderna COVID-19 vaccine maintained antibodies through six months, including against variants of concern such as the Delta variant,” Stéphane Bancel, CEO of Moderna, said in a news release. “These data support the durable efficacy of 93% seen with the Moderna COVID-19 vaccine through six months. We expect that these data and the growing body of real-world evidence will help inform health regulators’ approaches to how and when to administer additional boosting doses.”
Researchers observed a trend among the oldest age group, finding lower levels against variants at six months, however, “importantly, many subjects in the oldest group retained neutralizing activity against the variants 6-months after the second vaccine dose,” the study reads.
“While additional studies will be needed to address the impact of new variants that will surely arise in areas of intense viral infection, our data are encouraging for the use of this vaccine in the face of viral variation,” the study continues.
However, the immune system has complexity extending beyond antibody levels, and study authors also noted that people with waning immune responses likely have B cells to aid in responding to variants, writing: “individuals who demonstrate waning immune responses over time are likely to have memory B cells capable of delivering an anamnestic response to those variants in the event of exposure to virus, or potentially with an additional dose of vaccine.”