Fonte: The Lancet
(Texto original, publicado em inglês)
Impact of influenza vaccination on hospitalised patients in South America
Worldwide, influenza virus accounts for 7% of all acute lower respiratory tract infections, and 4% of deaths due to acute lower respiratory tract infections in children younger than 5 years.1 In The Lancet Infectious Diseases, Annette K Regan and colleagues2 report the results of an interesting multicentre, multicountry, surveillance study aiming to assess whether influenza vaccination is associated with illness attenuation. The study involved 41 sentinel sites across four countries in South America as part of REVELAC-i (Red para la Evaluación de Vacunas En Latino América y el Caribe—influenza), a network that annually evaluates influenza vaccine effectiveness using a test-negative design.
The design used in Regan and colleagues’ study is a convenient and efficient tool for estimating vaccine effectiveness and minimising selection bias; however, given that test-negative design studies are observational in nature, causal estimates can be biased because of confounding factors. To reduce such bias, the authors correctly adjusted for potential confounders.
Based on 2747 patients from Argentina, Brazil, Chile, or Paraguay, with laboratory-confirmed influenza virus infection—comprising 649 children (aged 6–24 months), 520 adults (aged 18–64 years) with pre-existing medical conditions, and 1578 older adults (aged ≥65 years)—the results showed that influenza vaccination was associated with reduced odds of intensive care unit (ICU) admission or in-hospital death and shorter length of hospital stay, with these benefits varying by age group. Therefore, this work contributes to evidence documenting the benefits of influenza vaccination programmes.
Although the topic is not novel and several studies with similar aims have been published,3 continued evaluation of the effectiveness of influenza vaccines, especially for at-risk and diverse populations, is necessary. Regan and colleagues’ study2 is relevant because influenza vaccination is especially important in Hispanic or Latino populations who have been identified as having higher rates of hospitalisation from influenza. Studies by the US Centres for Disease Control and Prevention (CDC) have identified racial and ethnic disparities in rates of influenza-associated hospitalisation, ICU admission, and in-hospital death.4 The CDC has also reported that people living in areas with high poverty are at increased risk for severe outcomes from influenza,5 suggesting that socioeconomic status might be a factor contributing to higher influenza-related hospitalisation rates among these groups.
One interesting finding of Regan and colleagues’ study,2 not fully discussed, is that even partially vaccinated children had lower odds of ICU admission. These results imply that a single dose might still contribute to illness attenuation in children. Further research is needed in children in low-income countries where incomplete schemes of vaccination are common.
The authors observed lower odds of ICU admission among partially vaccinated children (adjusted odds ratio 0·64 [95% CI 0·44–0·92]) and fully vaccinated children (0·52 [0·28–0·98]) compared with their unvaccinated counterparts, but no statistically significant difference for vaccinated adults with pre-existing medical conditions (1·25 [0·93–1·67]) or vaccinated older adults (0·88 [0·72–1·08]), suggesting that the attenuation of disease severity associated with vaccination might be specific to certain target groups, seasons, or settings. These results should be examined carefully and interpreted with caution. According to WHO, people at risk for severe illness include pregnant women at any stage of pregnancy, children younger than 5 years, older adults (aged >65 years), and people with chronic medical conditions.6, 7
Several studies have shown evidence that people with asthma, heart disease, diabetes, or a number of other chronic health conditions are at an increased risk of developing serious complications of influenza that can result in hospitalisation or death.8 Martínez-Baz and colleagues9 reported that influenza vaccination in people with diabetes reduced the risk of influenza-related hospitalisation by around half. Regarding patients with asthma, influenza vaccination might prevent not only influenza infection, but also asthma attacks.10
Although in Regan and colleagues’ study2 all pre-existing medical conditions were grouped, the authors did not find significant differences among vaccinated versus unvaccinated adults with pre-existing conditions. In the study there were only 118 vaccinated adults with at least one pre-existing medical condition, and the results might thus have been influenced by the small sample size in this group.
The study did not include two at-risk populations: children aged 2–5 years (the authors included only those aged 6–24 months) and pregnant women. Further analyses including these populations are needed, because some Latin American countries do not target these groups for vaccination in their national vaccination schemes.
This work also emphasises the importance of international collaboration. In Mexico, after the 2009 H1N1 influenza pandemic, the Mexican Emerging Infectious Disease Clinical Research Network (LaRed) was established as a collaboration between the US National Institutes of Health and the Mexican Government, with the aim of conducting surveillance of infectious diseases. For Regan and colleagues’ study specifically, the collaborative effort necessitated financial and technical support to facilitate the collection of data; through these efforts, valuable data are collected that contribute to expanding each country’s vaccine recommendations to increase coverage among the general population.
Although the 2020–21 influenza season was mild, for future influenza seasons, it will be important to understand the effects of SARS-CoV-2 and influenza virus co-circulation on the epidemiology and morbidity of influenza. SARS-CoV-2 and influenza viruses can realistically be expected to co-circulate for the foreseeable future, leading to the requirement for long-term public health policies contemplating the availability of influenza and COVID-19 vaccines.
