Table 2 Bayesian linear mixed interval-censored models on antibody titer trends after vaccination (n = 1763 with 7376 data points).

Fixed effects	Posterior median	95% CrI
(Intercept)	2.751	2.728	2.778
Time (elapsed 10 days)	− 0.019	− 0.028	− 0.010
Previous COVID-19 infection	0.346	0.335	0.355
Previous COVID-19 infection:Time	0.021	0.019	0.023
Post-infection days
0–6 days	− 0.317	− 0.324	− 0.310
7–89 days	0.353	0.344	0.363
90–179 days	0.283	0.278	0.289
Over 180 days	(omitted)
Prevalent strains at infection
Alpha variant	0.645	0.631	0.660
Delta variant	0.015	− 0.006	0.036
Omicron variant	0.631	0.619	0.642
Recent vaccine dose
4	0.360	0.344	0.377
5	0.464	0.459	0.472
Recent vaccine dose:Time
4:Time	0.009	0.006	0.012
5:Time	0.025	0.014	0.037
Age group (years)
Age 40–59	− 0.020	− 0.036	− 0.004
Age 60–79	− 0.122	− 0.129	− 0.114
Over 80	− 0.254	− 0.273	− 0.238
Age group (years):Time
Age 40–59:Time	− 0.002	− 0.009	0.004
Age 60–79:Time	− 0.005	− 0.009	0.000
Over 80:Time	− 0.009	− 0.016	− 0.003
Female sex	− 0.122	− 0.132	− 0.111
Female sex:Time	0.008	0.003	0.016

Random-effects parameters (unstructured)	Posterior median	95% CrI
Variance of random intercept	0.178	0.129	0.230
Covariance between random intercept and random slope	− 0.007	− 0.010	− 0.004
Variance of error term for time	0.003	0.003	0.003
Variance of the overall error term	0.190	0.175	0.207

References for the categorical variables are as follows:
No history of previous COVID-19 infection is the reference group for the post-infection days category.
Original strain is the reference group for the prevalent strains at infection category.
Dose of 3 is the reference group for the recent vaccine dose category.
Age < 40 years is the reference group for the age group category.
Male sex is the reference group for female sex.
Time, post-vaccination days (by 10 days), is a continuous variable from days 0 to 500.
The symbol “:” indicates interaction.
CrI, credible interval.

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