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Volume 32, Number 4—April 2026
Research Letter
Acute Febrile Illness Surveillance for Estimating Population Immunity, Dominican Republic, 2021
, Cecilia Then Paulino, Marietta Vasquez, William Duke, Petr Jarolim, Ronald Skewes Ramm, Adam Kucharski, and Colleen L. Lau
Table
Baseline characteristics of surveillance and survey participants before and after propensity score matching for study of acute febrile illness surveillance for estimating population immunity, Dominican Republic, 2021*
| Variable | Surveillance, n = 115 | Survey, unmatched, n = 962 | Survey, matched,† n = 575 |
|---|---|---|---|
| Age group, y | |||
| 0–14 | 10 (8.7) | 91 (9.5) | 55 (9.6) |
| 15–34 | 52 (45.2) | 316 (32.8) | 239 (41.6) |
| 35–54 | 29 (25.2) | 280 (29.1) | 156 (27.1) |
| >55 |
24 (20.9) |
275 (28.6) |
125 (21.7) |
| Median age, y (IQR) |
33 (25–52) |
40 (24–57) |
34 (22–53) |
| COVID-19 vaccines | |||
| None | 30 (26.1) | 149 (15.5) | 144 (25.0) |
| 1 | 5 (4.3) | 109 (11.3) | 31 (5.4) |
| 2 | 71 (61.7) | 603 (62.7) | 355 (61.7) |
| 3 | 9 (7.8) | 101 (10.5) | 45 (7.8) |
| Mean (+SD) |
1.5 (1.0) |
1.7 (0.9) |
1.5 (1.0) |
| Days since last vaccination, mean (+SD) |
62.1 (54.3) |
76.7 (44.7) |
73.8 (40.4) |
| Sex | |||
| F | 78 (67.8) | 658 (68.4) | 408 (71.0) |
| M |
37 (32.2) |
304 (31.6) |
167 (29.0) |
| Province | |||
| Espaillat | 60 (52.2) | 309 (32.1) | 203 (35.3) |
| San Pedro de Macorís | 52 (45.2) | 572 (59.5) | 318 (55.3) |
| Santiago |
3 (2.6) |
81 (8.4) |
54 (9.4) |
| Setting | |||
| Rural | 82 (71.3) | 486 (50.5) | 329 (57.2) |
| Urban |
31 (27.0) |
476 (49.5) |
246 (42.8) |
| Seroprevalence, mean (+SD) |
0.88 (0.33) |
0.94 (0.25) |
0.92 (0.27) |
| log10 spike antibody titer | |||
| Mean (+SD) | 2.4 (1.4) | 2.6 (1.2) | 2.5 (1.2) |
| Median (IQR) | 2.6 (1.7–3.2) | 2.7 (1.9–3.4) | 2.6 (1.9–3.2) |
*Values are no. (%) participants except as indicated. The study compared SARS-CoV-2 spike antibody data collected during July–October 2021 in the same Dominican Republic provinces from a longitudinal AFI surveillance system embedded in routine healthcare settings (“surveillance”) (4), which included routine blood collection for serologic testing; and a multistage, population-representative household serologic survey (“survey”) (1). Seroprevalence represents the percentage of participants with spike antibody titers above the manufacturer-specified cutoff (≥0.8 U/mL). IQR, interquartile range. †The matched survey dataset was generated through 1:5 nearest-neighbor propensity score matching of survey participants to surveillance participants, using age and number of COVID-19 vaccine doses as matching variables. Because only those variables were included in the propensity model, differences in other characteristics (e.g., province, setting, days since last vaccination) reflect inherent differences between the underlying sampling frames rather than confounding in the matched analysis. ‡Two surveillance participants were missing data for setting.