The World Health Organization (WHO) estimates 5–10 % of adults and 20–30 % of children become infected with influenza annually, resulting in 3–5 million severe cases and 290,000–650,000 deaths [1]. Approximately 82 % of hospital deaths from acute lower respiratory infections occur in low- and lower-middle income countries [2]. In Costa Rica from 2010 to 2015, the annual influenza-associated respiratory hospitalization rate was 99 per 100,000 people (95 % CI: 46–213 per 100,000) aged < 5 years, 15 per 100,000 (95 % CI: 8–26) aged 5–64 years, and 88 per 100,000 (95 % CI: 45–173) aged ≥ 65 years [3]. Diseases of the respiratory system constitute the fourth leading cause of death (3.4 per 10,000) in Costa Rica, accounting for 9 % of all deaths [4].

Pregnant women in all three trimesters are at increased influenza-related morbidity and mortality risk, particularly those with chronic medical conditions, which may be attributed to physiological, hormonal, and immunologic changes during pregnancy [5]. Influenza also increases risk of stillbirth [5]. WHO Strategic Advisory Group of Experts on Immunization (SAGE) and Centers for Disease Control and Prevention’s (CDC) Advisory Committee on Immunization Practices (ACIP) recommend influenza vaccination for pregnant women at any stage of pregnancy [6,7]. These recommendations are based on evidence of direct protection against severe disease to pregnant women and indirect protection to infants younger than six months through passive antibody transfer, the latter of whom are not eligible for influenza vaccination with currently licensed vaccines [8,9]. A systematic review of countries in the tropics demonstrated that vaccinating pregnant women prevented 50 % of laboratory-confirmed influenza in healthy mothers and 49–63 % in infants < 6 months [10]. SAGE and ACIP also recommend vaccinating healthcare workers to protect the individual, maintain continuity of healthcare services during epidemics, and protect vulnerable patients [6,7].

Despite these recommendations, vaccination coverage among pregnant women remains low worldwide, which may be attributed to misconceptions regarding vaccine efficacy or side effects, underestimating influenza severity, and lack of access to vaccines [11]. Many studies have shown direct physician recommendations are key reasons for vaccination among pregnant women [12,13], but healthcare workers with unfavorable attitudes or aversion to vaccination may be less likely to recommend vaccines to patients [14]. Few studies have examined factors affecting vaccination among both pregnant/postpartum women and prenatal care physicians from the same regions or healthcare facilities.

Unlike many middle-income countries, all governments in Central America have seasonal influenza vaccination programs, which generally follow SAGE recommendations. Costa Rica began influenza vaccination for risk groups in 2004 [15], including children 6–35 months of age, people with chronic diseases, adults > 60 years of age, pregnant women at any gestational age, and healthcare workers who provide direct care to patients [16]. Influenza vaccines are available free-of-charge for risk groups during national campaigns which begin in June and last for six weeks.

Currently, there are no studies evaluating factors affecting vaccination among pregnant women in Costa Rica. We therefore aimed to describe knowledge, attitudes, and practices (KAP) regarding seasonal influenza vaccination among postpartum women and healthcare personnel who provide prenatal care. We surveyed women in their immediate postpartum period instead of pregnant women to better evaluate vaccination coverage throughout pregnancy. Information resulting from this study will support the country’s authorities in prioritizing access, education, and communication strategies to facilitate influenza vaccination for these populations.

Costa Rica has a total area of 51,100 km² and is divided into seven provinces, 81 cantons, and 463 districts. It has a population of 5,151,000 [17]. San José is the capital and largest city with 1,441,000 residents. Public healthcare services have been provided by CCSS since 1993, which cover 87 % of the population [18]. Health expenditure accounts for 7.3 % of Costa Rica’s Gross Domestic Product and there are 2.9 physicians/1,000 population [17]. Costa Rica has an estimated birth rate of 14.3 births/1,000 population (2022), fertility rate of 1.9 children born/woman (2021), infant mortality rate of 8.6 deaths/1,000 live births (2021), and maternal mortality rate of 27 deaths/100,000 live births (2017) [17]. Seasonal influenza typically peaks in November, followed by a second smaller peak in July [19].

This study was approved by the Research Ethics committee of UVG (Protocol number 156-11-2016) and Center for Strategic Development and Information on Health and Social Security of CCSS (study code AB-1513-17). It was registered with the National Health Research Council of Costa Rica. Written informed consent was obtained for all participants.

Influenza vaccination coverage for postpartum women in Costa Rica (85.5 %) was in the upper range (1.7 %−88.4 %) reported in a systematic review of vaccination coverage among postpartum women across 21 studies [20]. Vaccination coverage for prenatal care physicians (57.9 %) was nearly identical to that reported for all healthcare workers (including non-obstetric) in direct contact with patients in Costa Rica (57.7 %) [21]. These findings are consistent with similar cross-sectional studies in Honduras reporting influenza vaccination coverage of 82.3 % and 52.0 % among postpartum women and healthcare workers [12,14].

The finding that postpartum women who were recommended vaccination by clinicians were over three times more likely to be vaccinated than women who were not is supported by other studies [11–13,20]. Vaccine safety concerns to mother and infant may be mitigated from direct provider recommendations, particularly from vaccinated healthcare workers [22]. Providers who are regularly vaccinated were shown to recommend vaccines more frequently to pregnant women [23]. Indeed, we found 95 % vaccination coverage among both postpartum women and physicians in Limón province, suggesting an association between healthcare providers’ confidence in vaccines and willingness to recommend vaccination. Although almost all physicians indicated they recommended vaccination to pregnant women, only three-quarters of postpartum women said they received recommendations which represents missed opportunities to improve coverage.

The most cited reason for non-vaccination among postpartum women was not being offered vaccination, which is consistent with other research [12,24]. A systematic review of maternal vaccination uptake (including non-influenza vaccines) found healthcare provider recommendations were the most mentioned reasons for vaccination among pregnant women and coverage was higher among those who received both recommendations and offers (63.4–73.6 %) than those who only received recommendations (33.5–47.5 %) [25]. Although almost all postpartum women had received prenatal care, vaccines may not always be available during prenatal care appointments. Indeed, 81 % of physicians had offered vaccinations during prenatal care appointments, but 33 % had also referred them to other CCSS healthcare facilities and 13 % to private providers. Vaccinations should be offered during prenatal care appointments concomitant with recommendations, so patients are not inconvenienced with additional appointments.

Counterintuitively and in contrast to most studies [20,26,27], postpartum women with higher education were significantly less likely to have been vaccinated for influenza than women with no formal education. Our finding is consistent, however, with a study of older adults in Honduras [28] and a systematic review of factors associated with maternal influenza vaccination in low- and middle-income countries, which found that women with higher education were 36–42 % less likely to be vaccinated than women with primary or less than primary education [11]. One study found that pregnant women with higher education were three times more likely to search for pregnancy advice on the internet compared to women with less than high school education and many do not discuss information with their providers [29]. Another study showed that 22 % of pregnant women intended to decline influenza vaccination following exposure to online media articles on vaccination during pregnancy [30]. Physicians should be aware of these issues so they can direct pregnant women to reputable websites.

Consistent with other studies [14,31], the most cited reasons for non-vaccination among physicians were busy schedules and not being offered vaccines. Focus groups suggested more staff are needed during vaccination campaigns as healthcare workers are overworked. Furthermore, although a trivalent inactivated vaccine was used in Costa Rica during vaccination campaigns, almost all physicians believed vaccination causes flu-like symptoms and 39 % declined vaccination for fear of adverse effects, which is in accord with other studies of healthcare workers [14,21,32]. Mistrust in vaccination may stem from exposure to adverse effects of vaccinations in online media, which has been shown to significantly increase vaccine hesitancy and refusal rates [33]. This study was also conducted in 2017 after a heightened influenza season in Costa Rica from influenza A (H1N1)pdm09 and H3N2, which may have affected perceptions of influenza vaccine effectiveness [34]. Healthcare facility trainings were associated with higher vaccination coverage and may serve as convenient venues for offering vaccines and addressing questions.

Most cited reasons for vaccination among postpartum women were protection for self and neonates. A greater proportion of women who perceived vaccines as safe were vaccinated than those who did not. Data collection began three weeks after the launch of vaccination campaigns, which includes educational content on social media networks, radio spots, and posters which may have increased vaccine knowledge and awareness.

Similar to a study in Honduras [12], postpartum women with other children vaccinated for influenza were more likely to be vaccinated than those without other vaccinated children. This may suggest that vaccines should be offered to pregnant women who visit a healthcare center to vaccinate their children. We also found that postpartum women vaccinated for tetanus were more likely to be vaccinated for influenza, which may suggest that patients with positive initial experiences with vaccines may be more likely to accept other vaccines. Other studies have shown that previous vaccination for influenza was associated with greater vaccination or intention to vaccinate during pregnancy [35,36].

This study had several limitations. First, this study was conducted five years ago. KAP regarding vaccination in Costa Rica might have changed in recent years following the COVID-19 pandemic. Second, we included postpartum women and prenatal care physicians from CCSS hospitals, which may not be representative of all postpartum women and prenatal care physicians in Costa Rica. Third, due to delays in authorizations for project implementation, we did not have time to sample enough participants for proposed sample size. Fourth, cross-sectional studies do not enable evaluation of temporality or causal inference. Fifth, we were unable to verify vaccination status of physicians, however, studies have shown strong concordance between self-reported vaccinations and those documented in registries [37]. Six, there may have been social desirability bias, which could explain the discrepancy between the proportion of clinicians who said they recommended vaccinations versus postpartum women who said they received recommendations. Seventh, stepwise logistic regression may be problematic if independent variables which have causal effects on vaccination were not statistically significant [38]. Finally, it was difficult to discern whether hierarchical relationships existed in the focus groups that could have influenced opinions. Notwithstanding these limitations, our study included both quantitative and qualitative components that demonstrated consistency between survey and focus groups. To our knowledge, this is the first study evaluating vaccination KAP during pregnancy in Costa Rica.

Pregnant women and their infants benefit from maternal influenza vaccination. Vaccination campaigns and provisions of free vaccines effectively increased knowledge and coverage among pregnant women in Costa Rica. To improve access, pregnant women should be offered vaccination during prenatal care appointments. Vaccines should also be offered to pregnant women who visit healthcare centers to vaccinate their other children, even if they do not attend prenatal care appointments. Additional out-reach promoting safety and efficacy of vaccination is needed using communication strategies tailored to local communities, which should involve engagement with community leaders.

Influenza vaccination uptake was considerably lower among prenatal care physicians. Educating healthcare workers about vaccine benefits for themselves and patients is needed to dispel common misconceptions and mitigate safety concerns. We propose offering vaccinations on nights and weekends, requiring healthcare workers who decline vaccination to wear surgical masks, and strengthening mobile vaccine teams within healthcare facilities, which will have lists of healthcare workers who should be vaccinated including students and volunteers, and whether they accepted or rejected vaccination. Individuals who decline vaccination should be referred to vaccine champions who support vaccination for more information. Strategic alliances between key healthcare actors, especially specialized and general hospitals, would facilitate dissemination of information regarding vaccine benefits. Enhancing surveillance systems and improving laboratory capacity for detection of influenza would allow optimization of timing of vaccination campaigns.