Table 1:

Clinical characteristics of study participants.

	T1 samples (pre-BA.1 wave)	T2 samples (post-BA.1 wave)
n	n = 16	n = 39
Age at enrolment (median, IQR)	51 [38–54]	47 [31–54]
Gender (% female)	87.5%	84.2%
Sampling dates	July - Sept 2021	July - Sept 2023
Vaccination history
1 vaccine dose (%, n)	100%	28.2% (n=11)
2 vaccine doses (%, n)	0%	56.4% (n=22)
3 vaccine doses (%, n)	0%	15.4% (n=6)
Months since last vaccination (median, IQR)	5.2 [5–6]	20.7 [20.2–24.4]
Infection history
Prior recorded infectiona (%, n)	56.2% (n=9)	56.4% (n=22)
Omicron BTI (%, n)	na	100% (n=39)
Months since last recorded infection (median, IQR)	8.4 [7–13]b	19.4 [17.8–19.9]c
Paired samples	n = 15
Months between T2 and T1 samples (median, IQR)	23.9 [23.3–24.1]

T1 samples were collected approximately 4–6 months prior to the Omicron BA.1 wave and T2 samples were collected 2 years later, approximately 1.5 years after the BA.1 wave (see Figure S1). The majority of participants (89.7%) were vaccinated with Ad26.COV2.S. Three participants received a heterologous vaccination regimen (Ad26.COV2.S and BNT162b2) and one participant received 3 doses of the BNT162b2 vaccine. Prior infection and breakthrough infection were determined by PCR (‘recorded infection’) or by Nucleocapsid seroconversion or a two-fold increase in Nucleocapsid-specific IgG.

IQR: Interquartile range; BTI: breakthrough infection;

^a: Ancestral SARS-CoV-2 or Beta variant infection; na: Not applicable;

^b: PCR data available for 5/9 participants with documented infection;

^c: PCR data available for 15/39 participants.