Abstract
Although influenza is a major public health concern, little is known about the use of spray live attenuated influenza vaccine (LAIV) among adults. For this reason, we conducted a systematic review and meta-analysis to investigate the efficacy and safety of LAIV, especially in adults with/without clinical conditions and children <2 years, with the final aim of possibly extending the clinical indications. PubMed/MEDLINE and Scopus were the two databases consulted through February 2021. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. A critical appraisal was conducted. Analyses were performed by using ProMeta3 software. Twenty-two studies were included, showing that LAIV was associated with a higher probability of seroconversion when compared with a placebo and considering the A/H1N1 serotype (pooled OR = 2.26 (95% CI = 1.12–4.54), p-value = 0.022; based on 488 participants, without heterogeneity (I2 = 0.0%)). The meta-analysis also confirmed no significant association with systemic adverse events. Only rhinorrhea, nasal congestion, and sore throat were significantly associated with LAIV compared to the placebo. Despite limited available evidence, LAIV has proved to be a safe and effective flu vaccination, also due to its very low invasiveness, and our review’s results can be considered a starting point for guiding future research and shaping forthcoming vaccination campaigns.
Highlights
Influenza is an acute respiratory infection caused by influenza viruses, which belong to the single stranded-RNA genome family of Orthomyxoviridae
Twenty-two studies were included, showing that live attenuated influenza vaccine (LAIV) was associated with a higher probability of seroconversion when compared with a placebo and considering the A/H1N1 serotype (pooled odds ratio (OR) = 2.26, p-value = 0.022; based on 488 participants, without heterogeneity (I2 = 0.0%))
After title and abstract screening, 144 articles were consulted in full at the end of the screening procedure: 22 articles were included in the systematic review [32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53], whereas 122 articles were excluded with reasons
Summary
Influenza is an acute respiratory infection caused by influenza viruses, which belong to the single stranded-RNA genome family of Orthomyxoviridae. As recommended by the World Health Organisation (WHO), annual vaccination is currently the most effective strategy to control seasonal influenza infections [2,3], especially for people at a greater risk of severe disease or complications when infected, i.e., pregnant women, children aged 65 years old), or subjects with underlying clinical conditions [4,5] To reduce their risk of contracting influenza [6] and prevent transmission to susceptible patients [7], influenza vaccination on healthcare workers is strongly encouraged, if not required, in many hospitals. Despite the development and widespread availability of safe and efficient vaccines, vaccination coverage, especially among the most vulnerable populations, is still far from the recommended threshold (at least 75% of the population) [8] This low coverage is one of the leading causes of the high burden of influenza, with a range of 250,000–645,000 estimated deaths every year from seasonal influenza-associated respiratory complications worldwide [9,10]
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