Figure 3.

Viral neutralization activity of vaccine-induced antibodies is weaker in older adults. A, Frequency of COVID-19–naive health care workers (blue) and older adults (orange), as well as convalescent participants (N Sero+; black) are shown as histograms. The proportion of participants in each group who displayed neutralizing activity against live SARS-CoV-2 (USA-WA1/2020 strain) in 3/3 wells at a 1:20 or higher plasma dilution is shown in the darkest color, while those displaying borderline activity (defined as neutralization in least 1 well at a 1:20 dilution) is shown in lighter color. Total number in each group is shown above each bar, with the number of participants displaying each activity shown within the bar. P values computed using Fisher exact test are shown above each comparison. B, Same data as the COVID-19 participants shown in A (where neutralization includes both yes and borderline categories) but plotted by age, and where neutralization is reported as the reciprocal log₂ dilution value. Samples that displayed no evidence of neutralization were coded as having a reciprocal dilution factor of 10 (3.32 log₂). Symbols are colored by vaccine received, which was significantly associated with neutralization activity after 1 dose (Table 2). Statistics were computed using ordinary least-squares regression. C and D, Same as A and B but for neutralization responses measured 1 month after 2 doses of mRNA vaccine and where neutralizing activity required inhibition of cytopathic effects in 3/3 wells at a 1:20 or higher plasma dilution. Abbreviations: COVID-19, coronavirus disease 2019; LLOQ, lower limit of quantification; Recip dil, reciprocal dilution; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; w/ nAb, with neutralizing antibodies.