The Association between Influenza Vaccination and the Risk of SARS-CoV-2 Infection, Severe Illness, and Death: A Systematic Review of the Literature

Flu vaccine administration in the period before SARS-CoV-2 infection and its outcomes: An umbrella review

Objective

The potential association between influenza vaccination and SARS-CoV-2 infection and related outcomes is still controversial. The aim of this umbrella review is to represent the impact of previous influenza vaccination and COVID-19 outcomes using evidence currently available in literature.

Methods

A literature search of MEDLINE, EMBASE, Scopus, Web of Science and Cochrane Library was conducted. The paper selection was conducted using the preferred reporting items for systematic reviews and meta-analyses (PRISMA) method by two-blinded authors. The quality of meta-analyses was assessed using the AMSTAR 2 scale (A MeaSurement Tool to Assess systematic Reviews). The outcomes investigated were SARS-CoV-2 infection after influenza vaccination, hospitalization, intensive care unit admission, mechanical ventilation and mortality.

Results

The literature research identified 7 ecological studies and 6 meta-analyses. All the ecological studies show a negative relationship between influenza vaccination and COVID-19. The meta-analyses suggest a protective action of influenza vaccination against SARS-CoV-2 infection. Regarding the outcomes evaluated, only two studies reported a statistically significant reduction of 12% and of 17% in hospitalization and intensive care unit admission, respectively. Regarding mechanical ventilation, three studies showed a risk reduction of 31%, 27% and 28%. A substantial reduction of mortality risk was also observed in one study.

Conclusions

These results suggest that influenza vaccination could be associated with reduced susceptibility to SARS-CoV-2 infection, mechanical ventilation and mortality. Our findings highlighted how the administration of flu vaccine in subjects at risk could lead to a reduction in mortality, particularly in the over 65y.

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.

Insights for COVID-19 in 2023

Predictions for a near end of the pandemic by the World Health Organization should be interpreted with caution. Current evidence indicates that the efficacy of a fourth dose of classical mRNA vaccines (BT162b2 or mRNA-1273) is low and short-lived in preventing SARS-CoV-2 infection in its predominant variant (Omicron). However, its efficacy is high against severe symptomatic infection, hospitalization and death. The new vaccines being introduced are bivalent and active against the Omicron variants. Potential new vaccines to be introduced in the coming year include a vaccine based on a recombinant protein that emulates the receptor binding domain of the Spike protein under development by the Spanish company Hipra, as well as vaccines for nasal or oral administration. Available information suggests that vaccines against COVID-19 can be administered in association with influenza vaccination without particular complications. New drugs against COVID-19, both antiviral and anti-inflammatory, are under investigation, but this does not seem to be the case with monoclonal antibodies. The indication to use masks in some circumstances will be maintained next year in view of the accumulation of scientific data on their efficacy. Finally, the long COVID or Post-COVID syndrome may continue to affect a very high proportion of patients who have had the disease, requiring combined diagnostic and therapeutic resources.

Health behaviors and the risk of COVID-19 incidence: A Bayesian hierarchical spatial analysis

OBJECTIVES

Effective infection control measures, based on a sound understanding of geographical community-specific health behavioral characteristics, should be implemented from the early stage of disease transmission. However, few studies have explored health behaviors as a possible contributor to COVID-19 infection in the spatial context. We investigated health behaviors as potential factors of COVID-19 incidence in the early phase of transmission in the spatial context.

METHODS

We extracted COVID-19 cumulative case data as of February 25, 2021-one day prior to nationwide COVID-19 vaccination commencement-regarding health behaviors and covariates, including health condition and socio-economic factors, at the municipal level from publicly available datasets. The spatial autocorrelation of incidence was analyzed using Global Moran's I statistics. The associations between health behaviors and COVID-19 incidence were examined using Besag-York-Mollie models to deal with spatial autocorrelation of residuals.

RESULTS

The COVID-19 incidence had positive spatial autocorrelation across South Korea (I = 0.584, p = 0.001). The results suggest that individuals vaccinated against influenza in the preceding year had a negative association with COVID-19 incidence (relative risk=0.913, 95 % Credible Interval=0.838-0.997), even after adjusting for covariates.

CONCLUSIONS

Our ecological study suggests an association between COVID-19 infection and health behaviors, especially influenza vaccination, in the early stage of COVID-19 transmission at the municipal level.

Mitigating co-circulation of seasonal influenza and COVID-19 pandemic in the presence of vaccination: A mathematical modeling approach

The co-circulation of two respiratory infections with similar symptoms in a population can significantly overburden a healthcare system by slowing the testing and treatment. The persistent emergence of contagious variants of SARS-CoV-2, along with imperfect vaccines and their waning protections, have increased the likelihood of new COVID-19 outbreaks taking place during a typical flu season. Here, we developed a mathematical model for the co-circulation dynamics of COVID-19 and influenza, under different scenarios of influenza vaccine coverage, COVID-19 vaccine booster coverage and efficacy, and testing capacity. We investigated the required minimal and optimal coverage of COVID-19 booster (third) and fourth doses, in conjunction with the influenza vaccine, to avoid the coincidence of infection peaks for both diseases in a single season. We show that the testing delay brought on by the high number of influenza cases impacts the dynamics of influenza and COVID-19 transmission. The earlier the peak of the flu season and the greater the number of infections with flu-like symptoms, the greater the risk of flu transmission, which slows down COVID-19 testing, resulting in the delay of complete isolation of patients with COVID-19 who have not been isolated before the clinical presentation of symptoms and have been continuing their normal daily activities. Furthermore, our simulations stress the importance of vaccine uptake for preventing infection, severe illness, and hospitalization at the individual level and for disease outbreak control at the population level to avoid putting strain on already weak and overwhelmed healthcare systems. As such, ensuring optimal vaccine coverage for COVID-19 and influenza to reduce the burden of these infections is paramount. We showed that by keeping the influenza vaccine coverage about 35% and increasing the coverage of booster or fourth dose of COVID-19 not only reduces the infections with COVID-19 but also can delay its peak time. If the influenza vaccine coverage is increased to 55%, unexpectedly, it increases the peak size of influenza infections slightly, while it reduces the peak size of COVID-19 as well as significantly delays the peaks of both of these diseases. Mask-wearing coupled with a moderate increase in the vaccine uptake may mitigate COVID-19 and prevent an influenza outbreak.

The impact of influenza vaccination on surgical outcomes in COVID-19 positive patients: An analysis of 43,580 patients

BACKGROUND

Multiple recent studies suggest a possible protective effect of the influenza vaccine against severe acute respiratory coronavirus 2 (SARS-CoV-2). This effect has yet to be evaluated in surgical patients. This study utilizes a continuously updated federated electronic medical record (EMR) network (TriNetX, Cambridge, MA) to analyze the influence of the influenza vaccine against post-operative complications in SARS-CoV-2-positive patients.

METHODS

The de-identified records of 73,341,020 patients globally were retrospectively screened. Two balanced cohorts totaling 43,580 surgical patients were assessed from January 2020-January 2021. Cohort One received the influenza vaccine six months-two weeks prior to SARS-CoV-2-positive diagnosis, while Cohort Two did not. Post-operative complications within 30, 60, 90, and 120 days of undergoing surgery were analyzed using common procedural terminology(CPT) codes. Outcomes were propensity score matched for characteristics including age, race, gender, diabetes, obesity, and smoking.

RESULTS

SARS-CoV-2-positive patients receiving the influenza vaccine experienced significantly decreased risks of sepsis, deep vein thrombosis, dehiscence, acute myocardial infarction, surgical site infections, and death across multiple time points(p<0.05, Bonferroni Correction p = 0.0011). Number needed to vaccinate (NNV) was calculated for all significant and nominally significant findings.

CONCLUSION

Our analysis examines the potential protective effect of influenza vaccination in SARS-CoV-2-positive surgical patients. Limitations include this study's retrospective nature and reliance on accuracy of medical coding. Future prospective studies are warranted to confirm our findings.

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

BACKGROUND

A possible link between influenza immunization and susceptibility to the complications of COVID-19 infection has been previously suggested owing to a boost in the immunity against SARS-CoV-2.

OBJECTIVE

This study aimed to investigate whether individuals with COVID-19 could have benefited from vaccination against influenza. We hypothesized that the immunity resulting from the previous influenza vaccination would boost part of the immunity against SARS-CoV-2.

METHODS

We performed a population-based cohort study including all patients with COVID-19 with registered entries in the primary health care (PHC) electronic records during the first wave of the COVID-19 pandemic (March 1 to June 30, 2020) in Catalonia, Spain. We compared individuals who took an influenza vaccine before being infected with COVID-19, with those who had not taken one. Data were obtained from Information System for Research in Primary Care, capturing PHC information of 5.8 million people from Catalonia. The main outcomes assessed during follow-up were a diagnosis of pneumonia, hospital admission, and mortality.

RESULTS

We included 309,039 individuals with COVID-19 and compared them on the basis of their influenza immunization status, with 114,181 (36.9%) having been vaccinated at least once and 194,858 (63.1%) having never been vaccinated. In total, 21,721 (19%) vaccinated individuals and 11,000 (5.7%) unvaccinated individuals had at least one of their outcomes assessed. Those vaccinated against influenza at any time (odds ratio [OR] 1.14, 95% CI 1.10-1.19), recently (OR 1.13, 95% CI 1.10-1.18), or recurrently (OR 1.10, 95% CI 1.05-1.15) before being infected with COVID-19 had a higher risk of presenting at least one of the outcomes than did unvaccinated individuals. When we excluded people living in long-term care facilities, the results were similar.

CONCLUSIONS

We could not establish a protective role of the immunity conferred by the influenza vaccine on the outcomes of COVID-19 infection, as the risk of COVID-19 complications was higher in vaccinated than in unvaccinated individuals. Our results correspond to the first wave of the COVID-19 pandemic, where more complications and mortalities due to COVID-19 had occurred. Despite that, our study adds more evidence for the analysis of a possible link between the quality of immunity and COVID-19 outcomes, particularly in the PHC setting.

Does Influenza Vaccination Reduce the Risk of Contracting COVID-19?

The concurrent timing of the COVID-19 pandemic and the seasonal occurrence of influenza, makes it especially important to analyze the possible effect of the influenza vaccine on the risk of contracting COVID-19, or in reducing the complications caused by both diseases, especially in vulnerable populations. There is very little scientific information on the possible protective role of the influenza vaccine against the risk of contracting COVID-19, particularly in groups at high-risk of influenza complications. Reducing the risk of contracting COVID-19 in high-risk patients (those with a higher risk of infection, complications, and death) is essential to improve public well-being and to reduce hospital pressure and the collapse of primary health centers. Apart from overlapping in time, COVID-19 and flu share common aspects of transmission, so that measures to protect against flu might be effective in reducing the risk of contracting COVID-19. In this study, we conclude that the risk of contracting COVID-19 is reduced if patients are vaccinated against flu, but the reduction is small (0.22%) and therefore not clinically important. When this reduction is analysed based on the risk factor suffered by the patient, statistically significant differences have been obtained for patients with cardiovascular problems, diabetics, chronic lung and chronic kidney disease; in all four cases the reduction in the risk of contagion does not reach 1%. It is worth highlighting the behaviour that is completely different from the rest of the data for institutionalized patients. The data for these patients does not suggest a reduction in the risk of contagion for patients vaccinated against the flu, but rather the opposite, a significant increase of 6%. Socioeconomic conditions, as measured by the MEDEA deprivation index, explain increases in the risk of contracting COVID-19, and awareness campaigns should be increased to boost vaccination programs.

Influenza Vaccination Uptake and Hesitancy among Healthcare Workers in Early 2021 at the Start of the COVID-19 Vaccine Rollout in Cape Town, South Africa

Vaccination attitudes among healthcare workers (HCWs) predict their level of vaccination uptake and intention to recommend vaccinations to their patients. To our knowledge, no study has been conducted in South Africa to assess hesitancy toward influenza vaccines among HCWs. We adapted a questionnaire developed and validated by Betsch and colleagues and used it to conduct online and face-to-face interviews among HCWs at the start of the COVID-19 vaccine rollout. Multivariate logistic regression was used to assess predictors of influenza vaccine hesitancy. Of 401 participants, 64.5% were women, 49.2% were nurses, and 12.5% were physicians. A total of 54.9% were willing to accept, 20.4% were undecided, and 24.7% intended to refuse influenza vaccination. Participants who were above 25 years of age and physicians were more likely to accept the vaccine. Key predictors of vaccine acceptance were confidence in the effectiveness, consideration of benefits and risks, and willingness to be vaccinated to protect others. Influenza vaccine hesitancy was highest in those who did not trust that influenza vaccines are safe. For future flu seasons, tailored education programs on the safety and effectiveness of flu vaccines targeting younger HCWs, could be vital to improving vaccine uptake.

Influenza Vaccination and COVID-19 Outcomes in People Older than 50 Years: Data from the Observational Longitudinal SHARE Study

Existing literature on the association between influenza vaccination and COVID-19 infection/outcomes is conflicting. Therefore, we aimed to investigate the association between influenza vaccination and COVID-19 outcomes in a large cohort of adults who participated in the SHARE (Survey of Health, Ageing, and Retirement in Europe). Information regarding influenza vaccination in the previous year, and medical and demographic characteristics, were self-reported. Positivity for COVID-19, symptomatology, and hospitalization were also ascertained using self-reported information. An adjusted logistic regression analysis (including 15 baseline factors or propensity score) was used to assess the association between influenza vaccination and COVID-19 outcomes. A total of 48,408 participants (mean age 67 years; 54.1% females) were included. The prevalence of influenza vaccination was 38.3%. After adjusting for 15 potential confounders, influenza vaccination was significantly associated with a lower risk of positivity for COVID-19 (OR = 0.95; p < 0.0001), symptomatic forms (OR = 0.87; p < 0.0001), and hospitalization for COVID-19 (OR = 0.95; p < 0.0001). The results were similar when using a propensity score approach. In conclusion, influenza vaccination may be beneficial for the prevention of COVID-19, as the present study found that influenza vaccination was associated with a small/moderate lower risk of COVID-19 infection and adverse outcomes.

Influence of influenza vaccine and comorbidity on the evolution of hospitalized COVID-19 patients⋆

Background and objective

The COVID-19 coronavirus disease outbreak is evolving around the world. Objective: To evaluate the associations between influenza vaccination and other factors and the risk of mortality in hospitalized COVID-19 patients.

Materials and methods

Retrospective observational study. This study was conducted among hospitalized patients with COVID-19 at Hospital La Mancha Centro between March 5 and 25, 2020. Information on influenza vaccination was extracted from electronic medical records. We used a multivariate logistic regression to explore the association between influenza vaccination and mortality from COVID and other risk factors.

Results

410 patients were included. Influenza vaccine had no effect among COVID-19 hospitalized patients [OR: 1.55 (95%CI: 0.96–2.48; p = 0.071)]. Increasing hospital mortality was associated with older age [OR: 1.05 (95% CI 1.02–1.07), per year increase; p < 0.001)], Charlson ≥3 [OR: 1.84 (95%CI: 1.07–3.15, p = 0.027)] and heart failure on admission [OR: 6 (IC95%: 1.6–21.7; p = 0.007)].

Conclusions

Influenza vaccine had no effect among COVID-19 hospitalized patients. The risk factors identified were older age, higher comorbidity and heart failure on admission.

Estimating the impact of influenza on the epidemiological dynamics of SARS-CoV-2

As in past pandemics, co-circulating pathogens may play a role in the epidemiology of coronavirus disease 2019 (COVID-19), caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In particular, experimental evidence indicates that influenza infection can up-regulate the expression of ACE2-the receptor of SARS-CoV-2 in human cells-and facilitate SARS-CoV-2 infection. Here we hypothesized that influenza impacted the epidemiology of SARS-CoV-2 during the early 2020 epidemic of COVID-19 in Europe. To test this hypothesis, we developed a population-based model of SARS-CoV-2 transmission and of COVID-19 mortality, which simultaneously incorporated the impact of non-pharmaceutical control measures and of influenza on the epidemiological dynamics of SARS-CoV-2. Using statistical inference methods based on iterated filtering, we confronted this model with mortality incidence data in four European countries (Belgium, Italy, Norway, and Spain) to systematically test a range of assumptions about the impact of influenza. We found consistent evidence for a 1.8-3.4-fold (uncertainty range across countries: 1.1 to 5.0) average population-level increase in SARS-CoV-2 transmission associated with influenza during the period of co-circulation. These estimates remained robust to a variety of alternative assumptions regarding the epidemiological traits of SARS-CoV-2 and the modeled impact of control measures. Although further confirmatory evidence is required, our results suggest that influenza could facilitate the spread and hamper effective control of SARS-CoV-2. More generally, they highlight the possible role of co-circulating pathogens in the epidemiology of COVID-19.

The Effect of Influenza Vaccination on COVID-19 Morbidity, Severity and Mortality: Systematic Review and Meta-Analysis

Coronavirus disease 2019 (COVID-19) pandemic is rapidly developing worldwide with a high mortality rate. In this meta-analysis study, the effect of influenza vaccination on the prevention of COVID-19 and its consequences in patients were investigated. The systematic search for this study was performed from November 2019 to 25 November 2020, in the databases of Medline, PubMed, Scopus, Web of Science, Embase, Ebsco, Cochrane and medRxiv. Search terms used included COVID-19, coronavirus, SARS-CoV-2, covid, influenza, flu, grippe and vaccine. The present study examined the association between influenza vaccination and COVID-19 including COVID-19 infection, mortality, hospitalisation and intensive care unit (ICU) admission. Finally, the pooled estimates for different outcomes were calculated by the software for statistics and data science (STATA) version 15 and I2 was used to determine the heterogeneity. By analysing the data of articles, the pooled estimates of these data indicated that influenza vaccination could lower probability of COVID-19 infection up to 24% (OR = 0.77; 95% CI: 0.65, 0.91), of death up to 32% (OR = 0.68; 95% CI: 0.42, 1.11), of the hospitalisation up to 25% (OR = 0.75; 95% CI: 0.46; 1.23) and of admission to ICU up to 29% (OR = 0.71; 95% CI: 0.40, 1.27). Influenza vaccination can help decrease the COVID-19 infection and reduce hospitalisation and the need for ICU and mortality rates.

Risk of symptomatic severe acute respiratory syndrome coronavirus 2 infection not associated with influenza vaccination in the 2019-2020 season

The association of influenza vaccine and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection was assessed by test-negative design using data collected for a study of outpatient COVID-19-like illness with onset dates from June to September 2020. Multivariable logistic regression models examined the association between receipt of 2019-2020 influenza vaccine and PCR-confirmed SARS-CoV-2 with adjustment for potential confounders. Receipt of influenza vaccine during the 2019-2020 influenza season was not associated with increased odds of SARS-CoV-2 infection in adults (aOR 0.83, 95% CI 0.63 to 1.10) or children (aOR 0.92, 95% CI 0.47 to 1.80).

Attitudes toward the SARS-CoV-2 and Influenza Vaccination in the Metropolitan Cities of Bologna and Palermo, Italy

Vaccine hesitancy (VH) is known to play a relevant role in thwarting the efforts toward reaching satisfactory influenza vaccination coverage, and has caused similar difficulties during the COVID-19 pandemic. This study aims to describe the phenomenon and produce insights on the reasons behind VH. A survey was administered between December 2020 and February 2021 to adults living in the cities of Bologna and Palermo. Of the 443 subjects enrolled, 47.3% were likely to get the influenza vaccination, while 75.6% were willing to receive the COVID-19 vaccination. The most frequent determinants that motivated the willingness to get the COVID-19 vaccine were trust in the safety of vaccines and belief that the vaccine is an effective tool. As for people’s unwillingness to be vaccinated, being exposed to information that produced doubts about the vaccine and lack of trust in a newly developed vaccine were the most frequently involved determinants. Statistically significant positive associations were found between the willingness to be vaccinated and postgraduate education and the propensity towards influenza vaccination. A negative association with being over 40 years old and of female gender was also found. These results might have an impact in better understanding individual reasons behind VH, identifying which categories are more exposed to it and which strategies should be implemented.

Influenza vaccine during the 2019-2020 season and COVID-19 risk: A case-control study in Québec

Background

We carried out a case-control study that examined whether receipt of the inactivated influenza vaccine during the 2019-2020 season impacted on the risk of coronavirus disease 2019 (COVID-19), as there was a concern that the vaccine could be detrimental through viral interference.

Methods

A total of 920 cases with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (diagnosed between March and October 2020) and 2,123 uninfected controls were recruited from those who were born in Québec between 1956 and 1976 and who had received diagnostic services at two hospitals (Montréal and Sherbrooke, Québec). After obtaining consent, a questionnaire was administered by phone. Data were analyzed by logistic regression.

Results

Among healthcare workers, inactivated influenza vaccine received during the previous influenza season was not associated with increased COVID-19 risk (AOR: 0.99, 95% CI: 0.69-1.41). Among participants who were not healthcare workers, influenza vaccination was associated with lower odds of COVID-19 (AOR: 0.73, 95% CI 0.56-0.96).

Conclusion

We found no evidence that seasonal influenza vaccine increased the risk of developing COVID-19.

HIV self-testing in Ottawa, Canada used by persons at risk for HIV: The GetaKit study

Background

The Public Health Agency of Canada estimates that about 87% of persons living with human immunodeficiency virus (HIV) in Canada have been diagnosed, which is well below the Joint United Nations Programme on HIV/AIDS target to have 95% of HIV-positive persons diagnosed. Research has shown that HIV self-testing may help increase such diagnoses, especially among the populations who are most affected by HIV. The objective of the study was to determine the uptake and diagnosis outcomes associated with free HIV self-testing.

Methods

We developed the first online mailout free HIV self-testing program in Canada and implemented it in Ottawa. This project ran through the website, www.GetaKit.ca. We intended to recruit 150-400 participants over a 6-12-month period, estimating that this number would yield between 0-1 positive test results (expected positivity rate of 0.08%).

Results

Between July 20, 2020 and April 1, 2021, 1,268 people accessed the GetaKit website and verified their eligibility. In total, 600 persons were eligible and 405 ordered an HIV kit. Of those who ordered a kit, 399 completed a baseline survey. Overall, 71% of these participants were members of HIV priority groups. For test results, 228 persons reported test results, with one being positive, for a positivity rate of 0.24% overall and 0.44% of reported results. These rates exceed that normally observed in Ottawa.

Conclusion

Self-testing of HIV can be effectively delivered through a website. Such an intervention will also be used by persons with undiagnosed infections and appears to do so at a rate higher than that observed by other means of testing. Self-testing of HIV may therefore help Canada achieve the United Nations 95-95-95 targets.

Impact that the COVID-19 pandemic on routine childhood vaccinations and challenges ahead: A narrative review

Aim

To document the decline in vaccination coverage in the first months of 2020 as an indirect effect of the COVID‐19 pandemic.

Methods

We performed a literature review in medical databases. Overall, 143 articles were initially retrieved, out of which 48 were selected and included in the review.

Results

Our review retrieved similar data in many countries worldwide, and, globally, preliminary data from the first 4 months of 2020 indicate a decline in diphtheria‐tetanus‐pertussis coverage, generally considered the marker of vaccination coverage across countries. World Health Organization recommends maintaining vaccination services, prioritising primary series vaccinations especially for measles‐rubella or poliomyelitis, but it also lets each country decide whether to maintain the immunisation services evaluating the current epidemiology of vaccine‐preventable diseases and the COVID‐19 local transmission scenario. Successively, recovering of vaccinations should be planned. Moreover, during the pandemic, influenza vaccination should be promoted as a central public health measure.

Conclusion

Future challenges will be to maintain the vaccination programmes, especially in children younger than 2 years old and adolescents, to plan the recovery of vaccinations for subjects who postponed them during the lockdown, and to early identify any vaccine‐preventable disease outbreak.

Association of Influenza Vaccination and Prognosis in Patients Testing Positive to SARS-CoV-2 Swab Test: A Large-Scale Italian Multi-Database Cohort Study

To investigate the association of the 2019-2020 influenza vaccine with prognosis of patients positive for SARS-CoV-2A, a large multi-database cohort study was conducted in four Italian regions (i.e., Lazio, Lombardy, Veneto, and Tuscany) and the Reggio Emilia province (Emilia-Romagna). More than 21 million adults were residing in the study area (42% of the population). We included 115,945 COVID-19 cases diagnosed during the first wave of the pandemic (February-May, 2020); 34.6% of these had been vaccinated against influenza. Three outcomes were considered: hospitalization, death, and intensive care unit (ICU) admission/death. The adjusted relative risk (RR) of being hospitalized in the vaccinated group when compared with the non-vaccinated group was 0.87 (95% CI: 0.86-0.88). This reduction in risk was not confirmed for death (RR = 1.04; 95% CI: 1.01-1.06), or for the combined outcome of ICU admission or death. In conclusion, our study, conducted on the vast majority of the population during the first wave of the pandemic in Italy, showed a 13% statistically significant reduction in the risk of hospitalization in some geographical areas and in the younger population. No impact of seasonal influenza vaccination on COVID-19 prognosis in terms of death and death or ICU admission was estimated.

Influence of influenza vaccine and comorbidity on the evolution of hospitalized COVID-19 patients

Antecedentes y objetivo

El brote de la enfermedad COVID-19 está evolucionando en todo el mundo. El objetivo del estudio es evaluar la asociación entre la vacunación antigripal y el riesgo de mortalidad en pacientes con COVID-19 hospitalizados, así como otros factores de riesgo.

Materiales y métodos

Estudio observacional retrospectivo. Se realizó entre pacientes hospitalizados con COVID-19 del Hospital La Mancha Centro entre el 5 y el 25 de marzo de 2020. Utilizamos una regresión logística multivariable para explorar la asociación entre la vacunación antigripal y la mortalidad por COVID y otros factores de riesgo.

Resultados

Se incluyeron 410 pacientes. La vacunación antigripal no tuvo efecto entre los pacientes hospitalizados por COVID-19 (OR: 1,55 [IC 95%; 0,96-2,48; p = 0,071]). El aumento de la mortalidad intrahospitalaria se asoció con edad avanzada (OR: 1,05 [IC 95%; 1,02-1,07]), por cada aumento de año; p < 0,001, Charlson ≥ 3 (OR: 1,84 [IC 95%; 1,07-3,15, p = 0,027]) e insuficiencia cardíaca al ingreso (OR: 6 [IC 95%; 1,6-21,7; p = 0,007]).

Conclusiones

La vacuna antigripal no tuvo efecto en la evolución de pacientes hospitalizados por COVID-19. Los factores de riesgo identificados fueron la edad avanzada, mayor comorbilidad e insuficiencia cardíaca al ingreso.

The Association between Influenza Vaccination and COVID-19 and Its Outcomes: A Systematic Review and Meta-Analysis of Observational Studies

Influenza could circulate in parallel with COVID-19. In the context of COVID-19, some studies observed inverse associations between influenza vaccination and SARS-CoV-2 infection and clinical outcomes, while others did not. We conducted a meta-analysis to assess the association between influenza vaccination and SARS-CoV-2 infection and clinical outcomes, aiming to provide evidence for COVID-19 prevention and vaccination promotion. We searched four databases from inception to 10 March, 2021. Random effects and fixed effects models were used to pool odds ratios (ORs) and adjusted estimates with 95% confidence intervals (CIs). We used funnel plots to evaluate the publication bias, I2 statistics to evaluate the heterogeneity, and conducted subgroup analyses. Sixteen observational studies involving 290,327 participants were included. Influenza vaccination was associated with a lower risk of SARS-CoV-2 infection (pooled adjusted OR: 0.86, 95%CI: 0.81–0.91), while not significantly associated with adverse outcomes (intensive care: adjusted OR 0.63, 95%CI: 0.22–1.81; hospitalization: adjusted OR 0.74, 95%CI: 0.51–1.06; mortality: adjusted OR 0.89, 95%CI: 0.73–1.09). Our findings suggest that influenza vaccination is associated with a lower risk of SARS-CoV-2 infection. It is crucial for policy makers to implement strategies on influenza vaccination, for it may also have benefits for COVID-19 prevention.

Influenza and pneumococcal vaccinations are not associated to COVID-19 outcomes among patients admitted to a university hospital

In order to reduce the burden on healthcare systems and to support differential diagnosis with COVID-19, influenza and pneumococcal vaccinations were strongly recommended during the COVID-19 pandemic, especially in vulnerable groups. However, no univocal and conclusive evidence on the relationship between influenza and pneumococcal vaccinations and COVID‐19 outcomes exists. We evaluated the association between such vaccinations, COVID-19 hospitalization, intensive care unit admissions and deaths in a cohort (N = 741) of COVID-19 patients who had access to the emergency room of a large Italian University hospital between March 1, 2020 and June 1, 2020. Results show that influenza and pneumococcal vaccinations did not affect hospitalization, intensive care unit admission and deaths in COVID-19 patients in the overall sample and in those ≥65 years. The same pattern of results was confirmed considering timing of influenza vaccine administration, vaccination type, and number of uptakes in the last five vaccination campaigns. In conclusion, our study does not support an impact of influenza and pneumococcal vaccinations on COVID-19 outcomes.

Pneumococcal and Influenza Vaccination Rates and Pneumococcal Invasive Disease Rates Set Geographical and Ethnic Population Susceptibility to Serious COVID-19 Cases and Deaths

This study examines the relationship of pneumococcal vaccination rates, influenza, measles-mumps-rubella (MMR) diphtheria-tetanus-pertussis vaccinations (DTP), polio, Haemophilus influenzae type B (Hib), and Bacillus Calmette-Guerin (tuberculosis) vaccination rates to COVID-19 case and death rates for 51 nations that have high rates of COVID-19 testing and for which nearly complete childhood, at-risk adult and elderly pneumococcal vaccination data were available. The study is unique in a large number of nations examined, the range of vaccine controls, in testing effects of combinations of vaccinations, and in examining the relationship of COVID-19 and vaccination rates to invasive pneumococcal disease (IPD). Analysis of Italian regions and the states of the United States were also performed. Significant positive correlations were found between IPD (but not lower respiratory infections) and COVID-19 rates, while significant negative correlations were found between pneumococcal vaccination and COVID-19 rates. Influenza and MMR vaccination rates were negatively correlated with lower respiratory infection (LRI) rates and may synergize with pneumococcal vaccination rates to protect against COVID-19. Pneumococcal and influenza vaccination rates were independent of other vaccination rates. These results suggest that endemic rates of bacterial pneumonias, for which pneumococci are a sentinel, may set regional and national susceptibility to severe COVID-19 disease and death.

Association between Influenza Vaccination and Positive SARS-CoV-2 IgG and IgM Tests in the General Population of Katowice Region, Poland

The explanation of the potential interaction between the influenza vaccine and SARS-CoV-2 infection is urgently needed in the public health. The objective of the study is to compare the occurrence of positive SARS-CoV-2 IgG and IgM tests in subjects with and without recent (last year) seasonal influenza vaccinations. In a cross-sectional study located in three large towns of Silesian Voivodeship (Poland), we studied 5479 subjects in which 1253 (22.9%) had a positive anti-SARS-CoV-2 IgG test and 400 (7.3%) had a positive anti-SARS-CoV-2 IgM test. Seasonal influenza vaccination remains an independent factor protecting against positive IgG tests (OR = 0.68; 0.55–0.83). The effect is not apparent with IgM antibodies. The obtained results confirmed that the serological status of SARS-CoV-2 infection depends on vaccination against seasonal influenza.

Association between Influenza Vaccination and Positive SARS-CoV-2 IgG and IgM Tests in the General Population of Katowice Region, Poland

The explanation of the potential interaction between the influenza vaccine and SARS-CoV-2 infection is urgently needed in the public health. The objective of the study is to compare the occurrence of positive SARS-CoV-2 IgG and IgM tests in subjects with and without recent (last year) seasonal influenza vaccinations. In a cross-sectional study located in three large towns of Silesian Voivodeship (Poland), we studied 5479 subjects in which 1253 (22.9%) had a positive anti-SARS-CoV-2 IgG test and 400 (7.3%) had a positive anti-SARS-CoV-2 IgM test. Seasonal influenza vaccination remains an independent factor protecting against positive IgG tests (OR = 0.68; 0.55-0.83). The effect is not apparent with IgM antibodies. The obtained results confirmed that the serological status of SARS-CoV-2 infection depends on vaccination against seasonal influenza.

Association between Influenza Vaccination and Positive SARS-CoV-2 IgG and IgM Tests in the General Population of Katowice Region, Poland

The explanation of the potential interaction between the influenza vaccine and SARS-CoV-2 infection is urgently needed in the public health. The objective of the study is to compare the occurrence of positive SARS-CoV-2 IgG and IgM tests in subjects with and without recent (last year) seasonal influenza vaccinations. In a cross-sectional study located in three large towns of Silesian Voivodeship (Poland), we studied 5479 subjects in which 1253 (22.9%) had a positive anti-SARS-CoV-2 IgG test and 400 (7.3%) had a positive anti-SARS-CoV-2 IgM test. Seasonal influenza vaccination remains an independent factor protecting against positive IgG tests (OR = 0.68; 0.55-0.83). The effect is not apparent with IgM antibodies. The obtained results confirmed that the serological status of SARS-CoV-2 infection depends on vaccination against seasonal influenza.

Seroprevalence of Anti-SARS-CoV-2 Antibodies in a Random Sample of Inhabitants of the Katowice Region, Poland

Lack of knowledge around seroprevalence levels of COVID-19 in Poland was the reason for the implementation of a seroepidemiological study in the Katowice Region (2,100,000 inhabitants). In October-November 2020, a questionnaire examination and measurement of anti-SARS-CoV-2 IgG and IgM antibodies were performed in a random sample of the general population (n = 1167). The objectives of the study were to estimate the prevalence of IgG and IgM antibodies and to assess their host-related correlates. The prevalence of IgG seropositivity was 11.4% (95% CI: 9.5-13.2%) and IgM seropositivity was 4.6% (95% CI: 3.5-5.8%). Diagnosis of COVID-19 was found in 4.8% of subjects. A positive IgG test was statistically significantly associated with age (inverse relationship), a person's contact with a COVID-19 patient, quarantine, and two symptoms in the past: fever and loss of smell/taste. Positive IgG tests were less prevalent in subjects who had diagnoses of arterial hypertension, diabetes, or rheumatologic disorders. IgM test positivity was associated with quarantine and loss of smell/taste only with no effect of chronic diseases found. In Poland, in the period October-November 2020, the prevalence of SARS-CoV-2 infection was larger than earlier estimates obtained in other European countries, probably reflecting the measurements obtained during the "second wave" of the epidemic.

Absence of association between 2019-20 influenza vaccination and COVID-19: Results of the European I-MOVE-COVID-19 primary care project, March-August 2020

BACKGROUND

Claims of influenza vaccination increasing COVID-19 risk are circulating. Within the I-MOVE-COVID-19 primary care multicentre study, we measured the association between 2019-20 influenza vaccination and COVID-19.

METHODS

We conducted a multicentre test-negative case-control study at primary care level, in study sites in five European countries, from March to August 2020. Patients presenting with acute respiratory infection were swabbed, with demographic, 2019-20 influenza vaccination and clinical information documented. Using logistic regression, we measured the adjusted odds ratio (aOR), adjusting for study site and age, sex, calendar time, presence of chronic conditions. The main analysis included patients swabbed ≤7 days after onset from the three countries with <15% of missing influenza vaccination. In secondary analyses, we included five countries, using multiple imputation with chained equations to account for missing data.

RESULTS

We included 257 COVID-19 cases and 1631 controls in the main analysis (three countries). The overall aOR between influenza vaccination and COVID-19 was 0.93 (95% CI: 0.66-1.32). The aOR was 0.92 (95% CI: 0.58-1.46) and 0.92 (95% CI: 0.51-1.67) among those aged 20-59 and ≥60 years, respectively. In secondary analyses, we included 6457 cases and 69 272 controls. The imputed aOR was 0.87 (95% CI: 0.79-0.95) among all ages and any delay between swab and symptom onset.

CONCLUSIONS

There was no evidence that COVID-19 cases were more likely to be vaccinated against influenza than controls. Influenza vaccination should be encouraged among target groups for vaccination. I-MOVE-COVID-19 will continue documenting influenza vaccination status in 2020-21, in order to learn about effects of recent influenza vaccination.

Value of Immunizations during the COVID-19 Emergency

Recent estimates by World Health Organization (WHO, Geneva, Switzerland) and United Nations International Children's Emergency Fund (UNICEF) show a significant decline in vaccinal coverage rates in both pediatric and adult populations. The interruption of vaccination services is reported in at least 68 countries, with the involvement of about 80 million children worldwide. The situation is alarming if we consider that already in the period preceding the pandemic, immunization programs slowed down in various areas of the world. For these reasons, there is the risk of overloading health systems, already under pressure from the pandemic emergency, by employing human and economic resources for the management of epidemic outbreaks from vaccine-preventable diseases. The restoration and integration of vaccination services, the immunization of susceptible individuals as well as the adoption of adequate monitoring and surveillance measures are the main activities adopted by different countries to address the current global health emergency.

Influenza Vaccination and Myo-Pericarditis in Patients Receiving Immune Checkpoint Inhibitors: Investigating the Likelihood of Interaction through the Vaccine Adverse Event Reporting System and VigiBase

Background: Evidence on whether the influenza vaccine could exacerbate immune-related adverse events, including myopericarditis (MP), in patients treated with immune checkpoint inhibitors (ICIs), is still conflicting. We explored this issue through a global real-world approach. Methods: We queried the Vaccine Adverse Event Reporting System (VAERS) and VigiBase to retrieve cases of MP in which the influenza vaccine and ICIs were recorded as suspect and were concomitantly reported. For the included cases, causality assessment and Drug Interaction Probability Scale (DIPS) algorithms were applied. Results: There were 191 and 399 reports of MP with the influenza vaccine that were retrieved (VAERS and VigiBase, respectively). No case of MP reporting the concomitant use of ICIs and the influenza vaccine was found in VAERS, while three cases of myocarditis were retrieved in VigiBase. All of the cases were unclassifiable for a causality assessment because of the lack of data concerning latency. According to the DIPS, one report was categorized as possible and two as doubtful. Conclusion: The paucity of cases coupled with the doubtful causality assessment make the potential interaction between influenza vaccines and ICIs in cancer patients negligible from clinical and epidemiological standpoints. These findings support the cardiovascular safety of the influenza vaccination, which remains strongly recommended in cancer patients, especially in the current COVID-19 era.

Influenza vaccination strategies for 2020-21 in the context of COVID-19

BACKGROUND

Influenza vaccination prevents people from influenza-related diseases and thereby mitigates the burden on national health systems when COVID-19 circulates and public health measures controlling respiratory viral infections are relaxed. However, it is challenging to maintain influenza vaccine services as the COVID-19 pandemic has the potential to disrupt vaccination programmes in many countries during the 2020/21 winter. We summarise available recommendations and strategies on influenza vaccination, specifically the changes in the context of the COVID-19 pandemic.

METHODS

We searched websites and databases of national and international public health agencies (focusing on Europe, North and South America, Australia, New Zealand, and South Africa). We also contacted key influenza immunization focal points and experts in respective countries and organizations including WHO and ECDC.

RESULTS

Available global and regional guidance emphasises the control of COVID-19 infection in immunisation settings by implementing multiple measures, such as physical distancing, hand hygiene practice, appropriate use of personal protective equipment by health care workers and establishing separate vaccination sessions for medically vulnerable people. The guidance also emphasises using alternative models or settings (eg, outdoor areas and pharmacies) for vaccine delivery, communication strategies and developing registry and catch-up programmes to achieve high coverage. Several novel national strategies have been adopted, such as combining influenza vaccination with other medical visits and setting up outdoor and drive through vaccination clinics. Several Southern Hemisphere countries have increased influenza vaccine coverage substantially for the 2020 influenza season. Most of the countries included in our review have planned a universal or near universal influenza vaccination for health care workers, or have made influenza vaccination for health care workers mandatory. Australia has requested that all workers and visitors in long term care facilities receive influenza vaccine. The UK has planned to expand the influenza programme to provide free influenza vaccine for the first time to all adults 50-64 years of age, people on the shielded patient list and their household members and children in the first year of secondary school. South Africa has additionally prioritised people with hypertension for influenza vaccination.

CONCLUSIONS

This review of influenza vaccination guidance and strategies should support strategy development on influenza vaccination in the context of COVID-19.