General characteristics of participants, total and by fieldwork period
| Variable | Total (n=481) | November-December 2020 (n=84) | February-April 2021 (n=397) | P value* |
| Sociodemographic and migration variables | ||||
| Age—years, mean (SD) | 33.2 (10.7) | 33.1 (10.5) | 33.3 (10.7) | 0.883 |
| Female (%) | 55.3 | 53.6 | 55.7 | 0.726 |
| Educational level (%) | 0.944 | |||
| None | 6.0 | 7.1 | 5.8 | |
| Primary or less | 38.9 | 36.9 | 39.3 | |
| Secondary or technical equivalent | 27.0 | 27.4 | 27.0 | |
| Preparatory or technical equivalent | 19.1 | 17.9 | 19.4 | |
| Some college or more | 8.9 | 10.7 | 8.6 | |
| Travelling with minors | 68.4 | 58.3 | 70.5 | 0.029 |
| Working in the past week (%) | 34.3 | 56.0 | 29.7 | <0.000 |
| Slept in a risky place in the past 3 months2 (%)† | 17.3 | 20.2 | 16.6 | 0.426 |
| Country of origin (%) | 0.051 | |||
| Mexico | 25.2 | 20.2 | 26.2 | |
| Honduras | 47.0 | 39.3 | 48.6 | |
| Guatemala | 10.4 | 11.9 | 10.1 | |
| El Salvador | 10.2 | 15.5 | 9.1 | |
| Other | 7.2 | 13.1 | 6.0 | |
| Was in migrant detention before coming to Tijuana (%) | 50.3 | 35.7 | 53.4 | 0.003 |
| Months in Tijuana, mean (SD) | 3.4 (1.0) | 7.7 (0.7) | 4.3 (0.4) | <0.001 |
| Access to sanitation and protective/risk behaviours | ||||
| Always has access to water for handwashing (%) | 92.5 | 96.4 | 91.7 | 0.374 |
| Always has access to soap (%) | 87.7 | 96.4 | 85.9 | 0.084 |
| Washed hands or used hand sanitiser frequently or very frequently (%) | 89.8 | 94.1 | 88.9 | 0.158 |
| Self-isolated at home or in a shelter frequently or very frequently (%) | 47.9 | 65.5 | 44.2 | <0.001 |
| Wore a mask when in public frequently or very frequently (%) | 93.4 | 92.9 | 93.5 | 0.843 |
| Used public transport never or rarely (%) | 40.8 | 29.8 | 43.1 | 0.024 |
| Visited crowded places never or rarely (%) | 80.3 | 82.1 | 79.9 | 0.631 |
| Health and COVID-related variables | ||||
| Diabetes (%) | 4.4 | 1.2 | 5.0 | 0.117 |
| Hypertension (%) | 7.7 | 6.0 | 8.1 | 0.510 |
| COPD (%) | 7.3 | 7.1 | 7.3 | 0.959 |
| Cardiovascular disease (%) | 2.1 | 2.4 | 2.0 | 0.831 |
| Obesity (%) | 4.8 | 10.7 | 3.5 | 0.005 |
| Thinks she/he has had COVID-19 (%) | 12.9 | 18.1 | 11.8 | 0.124 |
| Previously tested positive for SARS-CoV-2 (%)‡ | 11.4 | 11.1 | 11.4 | 0.977 |
| Positive for SARS-CoV-2 antibodies§ (%) | 53.0 | 46.3 | 54.5 | 0.181 |
| Positive SARS-CoV-2 RNA (nasal swab) (%) | 1.5 | 0 | 1.8 | 0.217 |
*Χ2 test, or t test, comparing between recruitment periods.
†Slept in a vehicle, correctional institution, drug treatment centre, streets/beach/canal.
‡Percentage calculated over those tested previously (9 in first period, 105 in second period).
§Percentage excludes six participants who had already received a COVID vaccine. Indeterminate results are also excluded.