Table 2. Summary of the full GEE Poisson regression model with covariates for sex, student group, initial vaccination series completion date, initial vaccine type, and week in the study period.
| Variable | Unadjusted IRRc | Multivariable GEE Poisson model | ||
|---|---|---|---|---|
| p-valued | aIRR | 95% CI for aIRR | ||
| Booster (ref = 0) | ||||
| 1 | 0.47 | <0.001 | 0.44 | [0.33, 0.58] |
| Sex (ref = Female) | ||||
| Male | 1.15 | >0.99 | 1.02 | [0.89, 1.18] |
| Student groupa (ref = UG-other) | ||||
| UG-frat/sor | 2.20 | <0.001 | 2.16 | [1.84, 2.54] |
| UG-athlete | 2.00 | <0.001 | 2.02 | [1.57, 2.60] |
| LA | 0.41 | <0.001 | 0.43 | [0.25, 0.73] |
| GM | 1.51 | <0.001 | 1.64 | [1.15, 2.32] |
| VM | 0.21 | <0.001 | 0.17 | [0.08, 0.37] |
| Month of initial vaccine series completionb (ref = May 2021) | ||||
| January 2021 | 1.15 | >0.99 | 1.53 | [0.44, 5.28] |
| February 2021 | 0.97 | >0.99 | 1.23 | [0.74, 2.07] |
| March 2021 | 1.40 | <0.001 | 1.48 | [1.15, 1.89] |
| April 2021 | 1.23 | <0.001 | 1.30 | [1.10, 1.55] |
| June 2021 | 0.82 | >0.99 | 0.95 | [0.69, 1.29] |
| July 2021 | 0.77 | >0.99 | 0.89 | [0.60, 1.31] |
| August 2021 | 0.87 | >0.99 | 0.86 | [0.56, 1.32] |
| September 2021 | 0.63 | 0.62 | 0.62 | [0.32, 1.20] |
| October 2021 | 0.93 | >0.99 | 1.02 | [0.29, 3.66] |
| November 2021 | 0.00 | <0.001 | <0.001 | [<0.001, <0.001] |
| Initial vaccine type (ref = BNT162b2) | ||||
| mRNA-1273 | 0.93 | >0.99 | 0.97 | [0.82, 1.15] |
| Ad26.COV2.S | 1.16 | >0.99 | 1.11 | [0.82, 1.49] |
| Other WHO-approved vaccines | 0.37 | 0.002 | 0.53 | [0.33, 0.87] |
| Week in the study period (ref = Week 0) | ||||
| Week 1 | 4.89 | <0.001 | 5.37 | [4.61, 6.25] |
| Week 2 | 1.52 | <0.001 | 2.57 | [1.63, 4.07] |
| Week 3 | 1.90 | <0.001 | 3.71 | [1.96, 7.01] |
aDescriptions for student group categories. UG-frat/sor: Undergraduate students affiliated with fraternities/sororities; UG-athlete: Undergraduate varsity athletes that have no affiliation with fraternities/sororities; UG-other: Other undergraduate students; LA: Professional students in the law school; GM: Postbaccalaureate professional students in the business school; VM: Professional students in the college of veterinary medicine.
bInitial vaccination series completion is the date of receiving 1 dose of Ad26.COV2.S or 2 doses of other WHO-approved vaccines.
cUnadjusted incidence rate ratios are computed from results of univariable GEE Poisson regression models.
dAdjusted using Bonferroni correction to address multiple comparisons.
aIRR, adjusted incidence rate ratio; GEE, generalized estimating equation; IRR, incidence rate ratio; WHO, World Health Organization.