Moderna's COVID-19 vaccine spurs immune response in older adults

Moderna manufacturing site
Investigators in Moderna's phase 1 trial of mRNA vaccine mRNA-1273 saw two solicited systemic grade 3 adverse events. (Moderna)

Moderna has published data from adults aged 56 years and older who received its COVID-19 vaccine. Results from the small cohort suggest the vaccine triggers comparable immune responses in younger and older adults.

Writing in The New England Journal of Medicine, the investigators running the phase 1 trial of mRNA vaccine mRNA-1273 described the expansion of the study to include 40 older adults. Age is associated with worse outcomes in COVID-19 patients, but vaccines can fail to confer immunity to older people, raising concerns that prophylactics will fail the demographic that most needs protecting. 

The expanded trial enrolled 20 adults aged 56 to 70 years and 20 adults aged 71 years and older. Ten subjects from each age group received a 25-μg dose, and 10 received the 100-μg dose Moderna took into phase 3.


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After the second dose, levels of binding antibodies in the participants entered the upper quarter of the responses seen in former COVID-19 patients who donated plasma. The link between antibody levels and immunity remains unclear, and the small size of the trial makes it impossible to draw firm conclusions. But the increase in antibody levels is an encouraging early sign of effectiveness.

The investigators also looked at the T-cell responses of the older subjects. By Day 43, levels of type 1 helper T cells in subjects who received the 100-μg dose had increased. The T-cell response in participants who received the 25-μg dose was more muted, particularly in people aged 71 years and older. The type 2 helper T-cell response was minimal in all doses and age groups.

Investigators saw two solicited systemic grade 3 adverse events: a case of fever in a person aged 56 to 70 years who received the 25-μg dose and fatigue in a participant aged 71 years or older who took the 100-μg dose. Another subject experienced grade 3 hypoglycemia “after fasting and vigorous exercise.” Investigators considered that adverse event to be unrelated to the vaccine.

Moderna’s phase 3 trial is stratifying its 30,000 participants based on whether they are over or under 65 years of age. Between 25% and 40% of subjects will either be aged over 65 years or be younger but be at increased risk from COVID-19 due to comorbidities such as chronic lung disease. Subjects aged 65 years and older are eligible regardless of whether they are at raised risk of severe COVID-19.  

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