This article describes the Gripometro, a tool created in 2011, which, through a population-based demographic study, allows the levels of influenza vaccine coverage in Spain to be monitored in a continuous way through weekly interviews starting at the beginning of each seasonal influenza vaccination campaign (14). It also makes it possible to determine the intention to vaccinate in these study groups, as well as the motivations and barriers to vaccination. Data collected using this tool during the 2018–2019 season are also presented, both in the general population and in healthcare workers (primary care doctors and nurses). The results of vaccination coverage obtained by the Gripometro during this season were mostly comparable with the official data presented by the Ministry of Health months later after the end of the vaccination campaign (15), thus demonstrating its usefulness in the near real-time monitoring of the percentage vaccination in Spain and, allowing to implement correcting measures or noticing stakeholders if needed.
The results for end-of-season coverage obtained in individuals ≥ 65 years were similar to the data officially published by the Ministry of Health (15); higher estimates were observed with the Gripometro only in the regions of Andalusia (60.2% vs. 49.0%) and Aragon (61.0% vs. 54.2%). These differences may be due to differences in the data collection methodology, or in the estimation of the population residing in the regions.
In terms of the end-of-season coverage, both the Gripometro data (56.0%) and the official data from the Ministry of Health (54.2%) indicated that only just over half of respondents were vaccinated against influenza during the study season. According to official data, it appears that the respondents who had not yet been vaccinated, but intended to do so (14.1%), did not eventually get vaccinated. Overall, the average vaccine coverage reached was 10% below the 65% target proposed by the Spanish Ministry of Health for this group, and 20% below the 75% target established by the WHO for this risk group (1, 8). This suggests that only half of the Spanish population ≥ 65 years benefit from the protection offered by the influenza vaccine, a decisive factor that undoubtedly contributes to the high impact on influenza mortality in this risk group (16).
The coverage recorded in the study in children under 5 years was 5%; these values are to be expected, since in Spain the influenza vaccine is only recommended in children with risk conditions (8). However, official data show that even in paediatric risk groups, vaccination remains low (17). In contrast, 66% of patients under 18 who were vaccinated did not have chronic conditions nor were they pregnant women, so they did not follow the official vaccination recommendations (8).
Among primary care healthcare workers, both doctors and nurses, the percentage of vaccination coverage was 39.8%, slightly higher than the official data provided by the Ministry of Health for the 2018-19 season, which was 35% (15). Either way, it is striking that almost half of respondents, 42.7% (44.8% of doctors and 40.2% of nurses), stated that although they had not yet been vaccinated, they intended to do so; however, they did not appear to have done so at all. As this was not a main objective of the study, the statistical power did not allow the estimation of vaccination coverage in healthcare workers, subjects with underlying disease or pregnant women by autonomous region. However, about 20% of this group was not considered to belong to a risk group or did not trust the effectiveness of the vaccine. In this regard, it seems clear that it is necessary to insist on informing and training healthcare workers about the evidence of the influenza vaccine and its benefits in risk groups, and to strengthen persuasive measures to achieve increased levels of vaccine coverage among healthcare workers and their patients. To this end, the influenza vaccination working group of the Ministry of Health’s Ponencia de Programa y Registro de Vacunaciones [Vaccination Programme and Registration Committee] has developed a project to better understand the factors that influence the decision to get vaccinated against influenza in Spain in the 2019-20 season (18). One of the phases includes a quantitative study of healthcare workers using an online survey sent to all autonomous communities (18). This group was targeted because of their involvement in both transmitting influenza and recommending vaccination. The results of this survey are not yet known, but are expected to be similar to those obtained by the Gripometro, given its similar methodology.
Traditional influenza vaccination coverage surveillance systems experience delays due to dependence on reports submitted by medical institutions and on records that are not updated quickly enough. Knowledge of coverage in real time enables rapid communication between public health agencies and local governments, facilitating the development of measures to improve coverage. Specifically, monitoring influenza vaccination coverage is important for early detection of anomalies and to propose alternatives. In this sense, the Gripometro is presented as a practical and highly useful tool that may be especially important in times such as the 2020–2021 and successive seasons, in which influenza could coexist with COVID-19. The influenza vaccine is a complementary key weapon of the Spanish National Health System in controlling the COVID-19 pandemic to prevent a possible collapse of health care. Both the Ministry of Health and the different autonomous regions have stepped up influenza vaccination during 2020-21 season (8). The data provided by the Gripometro allow close monitoring of influenza vaccine coverage, especially when traditional surveillance systems are mainly focused on COVID-19 epidemics (19).
Like all observational studies, the Gripometro has a number of limitations inherent to the methodology used. For the general population, some response bias may have occurred since it is a telephone survey; for example, people who chose not to get vaccinated may have been less likely to answer the questionnaire. Furthermore, the fact that calls were made only to landlines may have introduced a selection bias, since the profile of the population that has a landline is different from the one that has only a mobile phone (20). Specifically, multiple studies have shown that there are differences in sociodemographic and health indicators according to the type of phone available, with worse health indicators among the population who only have a mobile phone (21, 22). Given that a high percentage of Spanish households use mobile phones (97.4% in 2018 according to data from the Spanish National Institute of Statistics (23)) the results obtained through the Gripometro could be underestimated with respect to the total population resident in Spain. For future campaigns, the inclusion of mobile phones in the sampling framework should be assessed, in order to avoid selection bias affecting the representativeness of the results obtained.
In summary, the Gripometro is a robust research method that provides real data and trends for influenza vaccine coverage along with other useful information related to vaccination — such as information on attitudes or personal perceptions — in advance of the publication of official data by the Ministry of Health. Real-time tracking of the trend and percentages of vaccine coverage can trigger an almost immediate and continuous response in terms of applying corrective measures where appropriate or reinforcing awareness messages during the vaccination campaign. Additionally, the Gripometro provides coverage data for major population groups that are not available in official reports. In general, the information obtained with this methodology complements the official information provided by the Ministry of Health with regard to the design and planning of annual vaccination campaigns and taking preventive or corrective measures in the different risk groups.