Pfizer vaccine elicits lower antibody levels in older adults
The Pfizer-BioNTech COVID-19 vaccine elicited “relatively lower” antibody levels in adults aged 50 years or older than in adults aged younger than 50 years, researchers reported in JAMA Network Open.
“By contrast, there was no difference in post-boost antibody levels in older adults vs. younger adults who received” the Moderna vaccine, Nathan E. Richards, MD, and colleagues from the division of allergy and clinical immunology at the University of Virginia, wrote.
Richards and colleagues conducted a cohort that compared antibody responses among employees who were fully vaccinated with either of the COVID-19 messenger RNA vaccines.
Among 167 participants, 79 received the Pfizer vaccine and 88 patients received the Moderna vaccine. The median age of participants was 42 years (interquartile range, 32-57 years), with 63 people (38%) aged 50 years or older.
Overall, levels of IgG to SARS-CoV-2 receptor-binding domain were lower among those who received the Pfizer vaccine compared with those who received the Moderna at preboost blood draw (5.9 µg/mL [95% CI, 3.7-9.6 µg/mL] vs. 19.1 µg/mL [95% CI, 15.8-23.1 µg/mL]) and postboost blood draw 45.9 µg/mL [95% CI, 37-57 µg/mL] vs. 68.5 µg/mL [95% CI, 61.9-75.7 µg/mL]).
Those aged 50 years or older who received the Pfizer vaccine had preboost IgG levels that were lower than levels recorded among those aged younger than 50 years (2.1 µg/mL [95% CI, 1-4.3 µg/mL] vs. 10.2 [95% CI, 6-21.2 µg/mL]).
This was the same at postboost as well (31.1 µg/mL [95% CI, 19.9-48.7 µg/mL] vs. 59 µg/mL [95% CI, 48.8-71.4 µg/mL]).
“One explanation for the difference in immunogenicity observed in older adults could relate to the amount of mRNA used in the respective vaccines, with 30 g contained in [the Pfizer vaccine] and 100 g in [Moderna’s vaccine],” the authors wrote. “A limitation of this study is that the neutralizing antibodies were not measured; however, several groups have reported a strong correlation between SARS-CoV-2 binding and neutralizing antibodies.”
Perspective
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The extent to which in vitro observations, meaning the level of antibodies — in this case, binding antibodies — are predictive of events in life is always somewhat opaque. But what really matters is whether there are any critical differences then between the Pfizer and Moderna vaccines regarding what we need from these vaccines, which is protection against serious illness.
To date, all the data that have been either published or presented by the CDC show that these two vaccines are indistinguishable with regard to their ability to prevent serious illness.
So, I'm not sure what to make of this study. I don't think it really changes my opinion about how I view these vaccines, which is that they are largely indistinguishable. I mean, if it ended up being that these data were predictive of protection against serious disease — either in terms of the groups that were protected, or in terms of longevity of protection — then it would be of interest, but I think for right now, these are just in vitro data in search of clinical meaning.
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