Antibody Titers Before and After

[George K]

https://jamanetwork.com/journals/jama/fullarticle/2786096?guestAccessKey=8168799b-fe68-4f50-90a8-e8348fe03217&utm_source=silverchair&utm_campaign=jama_network&utm_content=covid_weekly_highlights&utm_medium=email

Results

Among the 97 study participants, the median age was 70 years (IQR, 67-74), and 61% were women (Table 1). Before the third dose (median, 221 days [IQR, 218-225] after the first vaccination), 94 participants (97%) were seropositive. The median titer level increased significantly after the third dose, from a median of 440 AU/mL (IQR, 294-923) to 25 468 AU/mL (IQR, 14 203-36 618) (P < .001), and all participants became seropositive (Table 1). No significant correlation was observed between age and IgG titers (R = −0.075; P = .47). No variable was significantly associated with higher IgG titers, including age, sex, days after first vaccination, and comorbidities (Table 2). No major adverse events were reported.

Discussion

This study found that a third BNT162b2 dose in adults aged 60 years and older was associated with significantly increased IgG titers after 10 to 19 days, with no major adverse events.

A third dose of the SARS-CoV-2 mRNA-1273 vaccine (Moderna) induced seropositivity in 49% of kidney transplant recipients who did not respond after 2 vaccine doses,3 although this observation cannot be generalized to older adults. In a study from Israel among 1 137 804 adults aged 60 years and older who had received 2 BNT162b2 doses 5 or more months earlier, a third dose was associated with lower rates of confirmed SARS-CoV-2 infections and severe illness.4 This study adds serologic data to the clinical data on response to a third dose in adults aged 60 years or older.

Study limitations include the small sample size, short follow-up, and lack of cellular immunity testing and neutralizing antibody testing. Although accumulating evidence suggests that IgG response is a correlate of disease protection,5 cellular immunity has also been suggested to play an important role in protecting against SARS-CoV-2.6