Outcomes of COVID-19 Infection in People Previously Vaccinated Against Influenza: Population-Based Cohort Study Using Primary Health Care Electronic Records

Influenza vaccination and COVID-19 infection risk and disease severity: A systematic review and multilevel meta-analysis of prospective studies

BACKGROUND

In light of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) pandemic, the influence of influenza vaccination on the risk and severity of Coronavirus Disease 19 (COVID-19) has been a subject of debate. This systematic review and meta-analysis of prospective studies aim to assess the association between influenza immunization and the risk of SARS-CoV-2 infection and subsequent COVID-19 disease severity.

METHODS

A comprehensive search of PubMed and Embase databases was performed to identify prospective studies published before March 2024. We focused on evaluating the effect of influenza vaccination on SARS-CoV-2 infection risk and severe COVID-19 outcomes, such as hospitalization and mortality. The analysis employed a multilevel random effects meta-analysis approach. The risk of bias assessment was conducted using the Newcastle-Ottawa Scale.

RESULTS

From an initial pool of 5,863 records, 14 studies were selected for inclusion. The aggregated data yielded a summary relative risk (SRR) that showed no significant protective correlation between influenza vaccination and SARS-CoV-2 infection risk (SRR 0.95, 95% confidence interval [CI] 0.81-1.11), COVID-19-associated hospitalization (SRR 0.90, 95% CI 0.68-1.19), or COVID-19-related mortality (SRR 0.83, 95% CI 0.56-1.23).

CONCLUSIONS

This systematic review and meta-analysis, based exclusively on prospective studies, demonstrates the lack of a proven protective effect of influenza vaccination against COVID-19 and related outcomes. Our results do not support a significant protective effect of influenza vaccination against the risk or severe outcomes of COVID-19.

Botulinum Toxin Type A (BoNT-A) Use for Post-Stroke Spasticity: A Multicenter Study Using Natural Language Processing and Machine Learning

We conducted a multicenter and retrospective study to describe the use of botulinum toxin type A (BoNT-A) to treat post-stroke spasticity (PSS). Data were extracted from free-text in electronic health records (EHRs) in five Spanish hospitals. We included adults diagnosed with PSS between January 2015 and December 2019, stratified into BoNT-A-treated and untreated groups. We used EHRead® technology, which incorporates natural language processing and machine learning, as well as SNOMED CT terminology. We analyzed demographic data, stroke characteristics, BoNT-A use patterns, and other treatments. We reviewed the EHRs of 1,233,929 patients and identified 2190 people with PSS with a median age of 69 years; in total, 52.1% were men, 70.7% had cardiovascular risk factors, and 63.2% had suffered an ischemic stroke. Among the PSS patients, 25.5% received BoNT-A at least once. The median time from stroke to spasticity onset was 205 days, and the time from stroke to the first BoNT-A injection was 364 days. The primary goal of BoNT-A treatment was pain control. Among the study cohort, rehabilitation was the most common non-pharmacological treatment (95.5%). Only 3.3% had recorded monitoring scales. In conclusion, a quarter of patients with PSS received BoNT-A mainly for pain relief, typically one year after the stroke. Early treatment, disease monitoring, and better data documentation in EHRs are crucial to improve PSS patients' care.

Examining the effectiveness and duration of adjuvanted vs. non-adjuvanted influenza vaccines in protecting older adults against symptomatic SARS-CoV-2 infection

Annual influenza vaccination is one of the main public health measures able to drastically reduce the burden of this infectious disease. Some evidence suggests 'trained immunity' triggered by influenza vaccine might reduce the risk of SARS-CoV-2 infection. Adjuvanted influenza vaccines are known to induce a broader cross-reactive immunity. No studies investigated the effect of adjuvanted vs. non-adjuvanted influenza vaccines on the risk of symptomatic SARS-CoV-2 infection. A case-control analysis nested in a cohort of subjects aged ≥65 years and immunized with adjuvanted or non-adjuvanted influenza vaccines was conducted. Although no statistically significant (OR = 0.87; P = .082) difference between the two vaccine types was observed for the 9-month follow-up period, a 17% (OR = 0.83; P = .042) reduction in the odds of COVID-19 was observed for adjuvanted vaccines with a 6-month follow-up. Further evidence is needed, but these results might have implications given the complexity of the upcoming winter seasons, in which the co-occurrence of influenza, SARS-CoV-2 and other respiratory infections (e.g., syncytial virus) might be unpredictable.

Vaccination against influenza viruses reduces infection, not hospitalization or death, from respiratory COVID-19: A systematic review and meta-analysis

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes COVID-19 and has brought a huge burden in terms of human lives. Strict social distance and influenza vaccination have been recommended to avoid co-infections between influenza viruses and SARS-CoV-2. Scattered reports suggested a protective effect of influenza vaccine on COVID-19 development and severity. We analyzed 51 studies on the capacity of influenza vaccination to affect infection with SARS-CoV-2, hospitalization, admission to Intensive Care Units (ICU), and mortality. All subjects taken into consideration did not receive any anti-SARS-CoV-2 vaccine, although their status with respect to previous infections with SARS-CoV-2 is not known. Comparison between vaccinated and not-vaccinated subjects for each of the four endpoints was expressed as odds ratio (OR), with 95% confidence intervals (CIs); all analyses were performed by DerSimonian and Laird model, and Hartung-Knapp model when studies were less than 10. In a total of 61 029 936 subjects from 33 studies, influenza vaccination reduced frequency of SARS-CoV-2 infection [OR plus 95% CI = 0.70 (0.65-0.77)]. The effect was significant in all studies together, in health care workers and in the general population; distance from influenza vaccination and the type of vaccine were also of importance. In 98 174 subjects from 11 studies, frequency of ICU admission was reduced with influenza vaccination [OR (95% CI) = 0.71 (0.54-0.94)]; the effect was significant in all studies together, in pregnant women and in hospitalized subjects. In contrast, in 4 737 328 subjects from 14 studies hospitalization was not modified [OR (95% CI) = 1.05 (0.82-1.35)], and in 4 139 660 subjects from 19 studies, mortality was not modified [OR (95% CI) = 0.76 (0.26-2.20)]. Our study emphasizes the importance of influenza vaccination in the protection against SARS-CoV-2 infection.

Association of dual COVID-19 and seasonal influenza vaccination with COVID-19 infection and disease severity

The clinical guideline states that COVID-19 vaccination can be administered concurrently with Influenza (flu) vaccination (dual vaccination). Using data from the 2021 National Health Interview Survey, we conducted descriptive analysis and multivariate logistic regressions to examine the association between dual vaccination status and self-reported COVID-19 infection and severity. Among 21,387 (weighted 185,251,310) U.S. adults, about 22% did not receive either the flu or COVID-19 vaccine, 6.0% received the flu vaccine only, 29.1% received the COVID-19 vaccine only, and 42.5% received both vaccines. In the multivariate analysis, individuals with dual vaccination (OR, 0.65, 95% CI, 0.56-0.75) and COVID-19 vaccine only (OR, 0.71, 95% CI, 0.61-0.82) were significantly less likely to report COVID-19 infection when compared with those unvaccinated. There was no significant difference in self-reported COVID-19 symptom severity by vaccination status. The results suggest that dual vaccination may be an effective strategy to reduce the contagious respiratory disease burden.