Table 1 Risk factors for pneumonia as defined in the study methodology

Sociodemographic factors

Maternal education

1) Did not finish high school (<11 years of schooling)

2) Finished high school (≥11 years of schooling)

Household crowding

Defined as ≥2 individuals sleeping in the same room as the child.

Basic sanitation

The disposal of bathroom/toilet waste in the household was classified according to whether a public sewage system/septic tank was present.

Maternal age

Based on the WHO concept of adolescence, maternal age was categorized into <19 years and ≥19 years.

Smoking in the home and maternal smoking

Whether any members of the household smoked and whether the child’s mother smoked.

Monthly family income

Total household income, i.e., considering the earnings of all individuals living in the household, categorized as ≤1 or >1 minimum wage. (The minimum wage is the lowest remuneration that employers may legally pay to workers per month. During the period corresponding to the data collection the range was U$ 210.00 to 230.00)

Child-related factors

Birthweight

A continuous numeric variable, recorded in grams, either obtained from the vaccination card, certificate of live birth, medical records or as reported by the child’s mother. Categorized as low (<2500 g) or normal birth weight.

Prematurity

Preterm is defined as babies born alive before 37 weeks of pregnancy are completed. This information was expressed as a dichotomous ordinal variable.

Exclusive Breastfeeding

The child’s mother or guardian was asked if she had exclusively breastfed the child during 4 months. This information was expressed as a dichotomous variable.

Nutritional status

Assessed according to the WHO child growth standards [26] using z-score calculations. According to a-2 z-score, the weight-for-age ratio was classified into two categories: very low or low weight for age and normal weight for age.

Previous respiratory disease and/or allergy

This was a nominal categorical variable obtained by the investigator, defined by the presence of asthma/wheezing, coughing for more than 1 month, tuberculosis, eczema, rhinitis or other conditions, as reported by the child’s parent/guardian.

Previous hospitalization

The child’s mother or guardian was questioned regarding whether the patient had been previously hospitalized for any reason.

10-valent pneumococcal conjugate vaccine

With respect to the pneumococcal conjugate vaccine, children were considered to have been vaccinated if they had received at least two doses prior to their first birthday or one dose after their first birthday [25].

Influenza vaccine

We considered that children who were immunized according to the immunization card received: a) at least one dose if they received the prime vaccination previously and had been immunized with two doses

Or

b) two doses of the prime vaccination Children under 6 months of age and those over 6 months of age who had not been immunized were classified as unvaccinated.