Post-vaccination myositis and myocarditis in a previously healthy male

Acute Bilateral Orbital Myositis Following Covid 19 Vaccination

The authors present a case of acute bilateral orbital myositis occurring 24 hours after the administration of the mRNA1273 vaccination for COVID 19. The patient was presented with right proptosis, with orbital imaging demonstrating bilateral enlargement of all the extraocular muscles. Serological investigation did not reveal a precipitating cause or underlying disease process. The presenting features resolved entirely following treatment with methylprednisolone and the patient remains asymptomatic.

Comparison of COVID-19 Vaccine-Associated Myocarditis and Viral Myocarditis Pathology

The COVID-19 pandemic has led to significant loss of life and severe disability, justifying the expedited testing and approval of messenger RNA (mRNA) vaccines. While found to be safe and effective, there have been increasing reports of myocarditis after COVID-19 mRNA vaccine administration. The acute events have been severe enough to require admission to the intensive care unit in some, but most patients fully recover with only rare deaths reported. The pathways involved in the development of vaccine-associated myocarditis are highly dependent on the specific vaccine. COVID-19 vaccine-associated myocarditis is believed to be primarily caused by uncontrolled cytokine-mediated inflammation with possible genetic components in the interleukin-6 signaling pathway. There is also a potential autoimmune component via molecular mimicry. Many of these pathways are similar to those seen in viral myocarditis, indicating a common pathophysiology. There is concern for residual cardiac fibrosis and increased risk for the development of cardiomyopathies later in life. This is of particular interest for patients with congenital heart defects who are already at increased risk for fibrotic cardiomyopathies. Though the risk for vaccine-associated myocarditis is important to consider, the risk of viral myocarditis and other injury is far greater with COVID-19 infection. Considering these relative risks, it is still recommended that the general public receive vaccination against COVID-19, and it is particularly important for congenital heart defect patients to receive vaccination for COVID-19.

The Incidence of Myocarditis Following an Influenza Vaccination: A Population-Based Observational Study

BACKGROUND AND OBJECTIVE

Recently, studies have pointed to a link between coronavirus disease 2019 vaccinations and myocarditis. Myocarditis following an influenza vaccine has been sporadically reported. However, it is not known whether this adverse event occurs among elderly individuals who have received influenza vaccines. We used a population-based database and a self-controlled case-series design to estimate the incidence of myocarditis following an influenza vaccination.

METHODS

Data were extracted from Taiwan's National Health Insurance Research Database. The study population consisted of elderly people aged ≥ 65 years who had de novo myocarditis, which required hospitalization, within 6 months after receiving an influenza vaccination between 2003 and 2017. The first 1-7, 1-14, and 1-42 days after vaccination were defined as risk intervals, and the other periods were defined as control intervals. Poisson regression was used to calculate the incidence rate ratio for myocarditis between the risk and control periods.

RESULTS

Within 180 days following a vaccination, 191 people were hospitalized for myocarditis among 19,678,904 people. In comparison with control intervals, the incidence rate ratios of an admission for myocarditis for days 1-7, 1-14, and 1-42 were 0.80 (95% confidence interval 0.36-1.81), 0.72 (95% confidence interval 0.39-1.32), and 0.73 (95% confidence interval 0.50-1.05), respectively. Subgroup analyses by sex, age, Charlson Comorbidity Index scores, and comorbidities did not yield significant differences in the incidence rate ratio.

CONCLUSIONS

Regardless of the post-vaccination time and underlying baseline characteristics, the incidence risk of myocarditis is not significantly increased in the elderly following an influenza vaccination.

Uncommon Side Effects of COVID-19 Vaccination in the Pediatric Population

Introduction

The rapid development of vaccines followed the Coronavirus disease 2019 (COVID-19) pandemic. There is still significant vaccine hesitancy, especially among parents. Large-scale pediatric population-based studies or reviews about vaccine side effects are limited.

Data sources and methods

The Centers for Disease Control and Prevention (CDC) recommends recipients or their providers notify possible adverse events to the Vaccine Adverse Event Reporting System (VAERS). We evaluated Delaware state data from the VAERS system for the pediatric age group.

Results

A total of 111 reports were reviewed, with summaries of the reported key side effects discussed, including seizures, myocarditis, stroke, multisystem inflammatory syndrome in children (MIS-C), chest pain, hematuria, menstrual disorder, appendicitis, behavioral and otological side effects, etc.

Conclusions

We noted the approximate prevalence of reported adverse events to be <0.2%. Further studies with larger sample sizes or those focused on each key side effect are needed to evaluate these side effects in detail. An open discussion about the possible side effects and reinforcing the individual, family, and community benefits are key to promoting COVID-19 vaccine acceptance.

COVID ‐19 vaccine‐associated myositis – a case report

Myositis is one of the uncommon adverse events following COVID‐19 vaccination, and its mechanism is still unclear. A strong clinical suspicion and further evaluation are important not only for early diagnosis and management but also for better understanding of the unprecedented effects of this novel vaccine. We present a case of myositis following the first dose of the ChAdOx1 nCoV‐19 Corona Virus Vaccine, evidenced by serology and MRI.

Recurring Weakness in Rhabdomyolysis Following Pfizer-BioNTech Coronavirus Disease 2019 mRNA Vaccination

Rhabdomyolysis is a well-known clinical syndrome of muscle injury. Rhabdomyolysis following coronavirus disease 2019 (COVID-19) vaccination has recently been reported. The patients’ weakness gradually subsided and did not recur. Rhabdomyolysis associated with COVID-19 vaccination has not been assessed by repeated magnetic resonance imaging (MRI) within a short time. We report a rare case of an older woman who developed recurring weakness with rhabdomyolysis after COVID-19 vaccination. A 76-year-old woman presented with myalgia 2 days after receiving a third dose of the COVID-19 vaccine. A physical examination showed weakness of the bilateral iliopsoas muscles. Her creatine kinase concentration was 9816 U/L. MRI showed hyperintensity of multiple limb muscles. She was treated with intravenous normal saline. Her symptoms disappeared within 3 days. However, MRI on day 4 of hospitalization showed exacerbation of the hyperintensity in the left upper limb muscles. On day 5 of hospitalization, weakness of the left supraspinatus and deltoid muscles appeared. MRI on day 8 of hospitalization showed attenuation of the hyperintensity in all muscles. Her weakness and elevated creatine kinase concentration disappeared by day 10. Repeated MRI over a short time may be useful to predict potential weakness and monitor the course of COVID-19 vaccine-induced rhabdomyolysis.

A case of myocarditis after COVID-19 vaccination: incidental or consequential?

Vaccination represents one of the fundamentals in the fight against SARS-CoV-2. Myocarditis has been reported as a rare but possible adverse consequence of different vaccines, and its clinical presentation can range from mild symptoms to acute heart failure. We report a case of a 29-year-old man who presented with fever and retrosternal pain after receiving SARS-CoV-2 vaccine. Cardiac magnetic resonance imaging and laboratory data revealed typical findings of acute myocarditis.

Cardiac Adverse Events after Vaccination—A Systematic Review

The Vaccine Adverse Event Reporting System database has been used to report adverse events following several vaccines. We studied the patient population predisposed to such reactions and how these reactions differ with respect to the vaccine type. We searched the electronic databases PubMed, EMBASE, and Scopus up to 9 July 2021 for any study describing cardiac adverse events attributed to the vaccination. A total of 56 studies met the criteria comprising 340 patients. There were 20 studies describing cardiac adverse events following smallpox vaccination, 11 studies describing adverse events after influenza vaccination, and 18 studies describing adverse events after COVID-19 vaccination. There was a total of six studies describing cardiac adverse events after the pneumococcal vaccine, tetanus toxoid, cholera vaccine, and rabies vaccine. Adverse events following influenza vaccination occurred more commonly in older females within an average duration of four days from vaccination. Pericardial involvement was the most reported adverse event. Adverse events following COVID-19 vaccination happened at a mean age of 42.7 years, more commonly in males, and mostly after a second dose. Adverse events following smallpox vaccination occurred more commonly in younger males, with an average onset of symptoms from vaccination around 16.6 days. Adverse events were mostly myopericarditis; however, the acute coronary syndrome has been reported with some vaccines.

Hemophagocytic Lymphohistiocytosis After Inactivated Influenza Vaccination in a Young Man Complicated by Severe Rhabdomyolysis

Hemophagocytic lymphohistiocytosis (HLH) is an immune response disorder that is usually fatal despite treatment. It is characterized by a dysregulation in natural killer (NK) T-cell function, causing activation of lymphocytes and histiocytes, resulting in a cytokine storm, end-organ damage, and eventually death. In this report, we describe the case of a previously healthy 38-year-old Caucasian man who presented with fever, nausea, vomiting, abdominal pain, myalgias, and weight loss for one week after inactivated influenza vaccination. The initial evaluation showed leukocytosis, lactic acidosis, and a severely elevated creatine kinase level (19,639 IU/L). The presentation was consistent with a diagnosis of sepsis, likely secondary to viral etiology and rhabdomyolysis. Subsequently, he rapidly deteriorated, requiring mechanical ventilation and developed refractory shock requiring pressor support and continuous veno-venous hemofiltration for acute kidney injury due to rhabdomyolysis. Later, he developed bicytopenia, hyperferritinemia, hypertriglyceridemia, and elevated inflammatory markers, raising the possibility of underlying HLH. Further tests showed low NK cell cytotoxicity and elevated sCD25. The H-score, which is a clinical tool to estimate the probability of HLH, showed an 88-93% probability of that potentially fatal disorder.

The patient was treated with pulse-dose corticosteroids, intravenous immunoglobulins (IVIGs), and anakinra. He had a prolonged and complicated hospital stay for about two months. However, he was able to slowly recover. We believe that he developed secondary HLH in the setting of vaccination. Although rare, an early suspicion of HLH leads to the early initiation of directed therapy with immunosuppressant that would limit morbidity and mortality.

Immunogenicity mechanism of mRNA vaccines and their limitations in promoting adaptive protection against SARS-CoV-2

Since the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19) in late 2019, hundreds of millions of people have been infected worldwide. There have been unprecedented efforts in acquiring effective vaccines to confer protection against the disease. mRNA vaccines have emerged as promising alternatives to conventional vaccines due to their high potency with the capacity for rapid development and low manufacturing costs. In this review, we summarize the currently available vaccines against SARS-CoV-2 in development, with the focus on the concepts of mRNA vaccines, their antigen selection, delivery and optimization to increase the immunostimulatory capability of mRNA as well as its stability and translatability. We also discuss the host immune responses to the SARS-CoV-2 infection and expound in detail, the adaptive immune response upon immunization with mRNA vaccines, in which high levels of spike-specific IgG and neutralizing antibodies were detected after two-dose vaccination. mRNA vaccines have been shown to induce a robust CD8⁺T cell response, with a balanced CD4⁺ T_H1/T_H2 response. We further discuss the challenges and limitations of COVID-19 mRNA vaccines, where newly emerging variants of SARS-CoV-2 may render currently deployed vaccines less effective. Imbalanced and inappropriate inflammatory responses, resulting from hyper-activation of pro-inflammatory cytokines, which may lead to vaccine-associated enhanced respiratory disease (VAERD) and rare cases of myocarditis and pericarditis also are discussed.

Myocarditis following rAd26 and rAd5 vector-based COVID-19 vaccine: case report

SARS‐CoV‐2 vaccines provide a safe solution with a major impact on reducing the spread of the virus and mild side effects. Research has shown rare cases of myocarditis after mRNA vaccines. This study presents a 29‐year‐old male with chest pain after 48 h of receiving rAd26 and rAd5 vector‐based COVID‐19 vaccine (Sputnik V vaccine). The electrocardiogram revealed ST‐segment elevation. Also, the laboratory screening was remarkable for elevated cardiac Troponin‐I level, and leukocytosis; and echocardiography depicted severe left ventricular systolic dysfunction. Overall, endomyocardial biopsy proved lymphocytic myocarditis such that the patient was successfully treated with immunosuppressive and guideline‐directed medical treatment.

COVID-19 Vaccine-Induced Pneumonitis, Myositis and Myopericarditis

A 63-year-old male, with no significant past history and not on any regular medications previously, had mild respiratory symptoms post the first dose of the AstraZeneca (Cambridge, England) coronavirus disease 2019 (COVID-19) vaccine, which were self-limiting. Following the second dose of the vaccine, he arrived at the emergency department (ED) with worsening shortness of breath.

During this admission, he was assumed to have interstitial lung disease due to a possible past history of occupational exposure. He responded to a short-term course of corticosteroids and antibiotics and was discharged home.

However, he reported again to the emergency department three weeks later, with persistent dyspnoea along with myalgia. His blood tests and imaging from scans suggested myositis, pneumonitis, and myopericarditis. Since he recently had the COVID-19 AstraZeneca vaccine, it was postulated as the most likely cause of the symptoms. He was managed with intravenous (IV) corticosteroids followed by oral corticosteroids with symptom resolution.

Cardiac Manifestations of Multisystem Inflammatory Syndrome in Children (MIS-C) Following COVID-19

Purpose of Review

To review the spectrum of cardiac manifestations and treatments of multisystem inflammatory syndrome in children (MIS-C) associated with coronavirus disease 2019 (COVID-19).

Recent Findings

Studies demonstrate that up to 80% of children with MIS-C may have cardiac involvement on a spectrum of severity. Cardiac manifestations include myocarditis, coronary artery aneurysms, conduction abnormalities, and arrhythmias. Current treatments, including inotropic support, immunomodulatory therapy, and anti-coagulation, have been effective at resolving these cardiac findings in the majority of patients. COVID-19 can also cause myocarditis in the acute stage of illness and recent descriptions of COVID-19 vaccine myocarditis have occurred.

Summary

Cardiac manifestations are common in MIS-C and should be assessed for at presentation and during the clinical course as indicated.

Case report: acute myocarditis following the second dose of mRNA-1273 SARS-CoV-2 vaccine

BACKGROUND

The SARS-CoV-2 pandemic has led to the development of the first mRNA vaccines used in humans. The vaccines are well tolerated, safe, and highly efficacious; however, post-marketing surveillance is revealing potential rare adverse effects. We report a case of symptomatic acute myocarditis following administration of the second dose of mRNA-1273 SARS-CoV-2 vaccine.

CASE SUMMARY

A 44-year-old man presented with chest pain and ST-segment elevation 4 days after receiving the second dose of mRNA-1273 SARS-CoV-2 Vaccine. Emergent coronary angiogram showed minimal coronary artery disease. Cardiac magnetic resonance imaging confirmed acute myocarditis. Diagnosis of vaccine-associated myocarditis was made given the temporal relationship and supportive treatment initiated. Follow-up at 1 month confirmed complete symptomatic recovery and echocardiogram demonstrated normalization of cardiac function.

DISCUSSION

Acute myocarditis should be considered in patients who present with chest pain or dyspnoea within days of receiving mRNA-1273 SARS-CoV-2 vaccination, especially after the second dose. This may be managed successfully with supportive therapies with complete recovery of cardiac function and symptoms. Further research is warranted to determine the mechanisms by which mRNA vaccines may cause myocarditis and for potential long-term cardiovascular injury.

Patients With Acute Myocarditis Following mRNA COVID-19 Vaccination

Importance

Vaccine-associated myocarditis is an unusual entity that has been described for the smallpox vaccine, but only anecdotal case reports have been described for other vaccines. Whether COVID-19 vaccination may be linked to the occurrence of myocarditis is unknown.

Objective

To describe a group of 7 patients with acute myocarditis over 3 months, 4 of whom had recent messenger RNA (mRNA) COVID-19 vaccination.

Design, Setting, and Participants

All patients referred for cardiovascular magnetic resonance imaging at Duke University Medical Center were asked to participate in a prospective outcomes registry. Two searches of the registry database were performed: first, to identify patients with acute myocarditis for the 3-month period between February 1 and April 30 for 2017 through 2021, and second, to identify all patients with possible vaccine-associated myocarditis for the past 20 years. Once patients with possible vaccine-associated myocarditis were identified, data available in the registry were supplemented by additional data collection from the electronic health record and a telephone interview.

Exposures

mRNA COVID-19 vaccine.

Main Outcomes and Measures

Occurrence of acute myocarditis by cardiovascular magnetic resonance imaging.

Results

In the 3-month period between February 1 and April 30, 2021, 7 patients with acute myocarditis were identified, of which 4 occurred within 5 days of COVID-19 vaccination. Three were younger male individuals (age, 23-36 years) and 1 was a 70-year-old female individual. All 4 had received the second dose of an mRNA vaccine (2 received mRNA-1273 [Moderna], and 2 received BNT162b2 [Pfizer]). All presented with severe chest pain, had biomarker evidence of myocardial injury, and were hospitalized. Coincident testing for COVID-19 and respiratory viruses provided no alternative explanation. Cardiac magnetic resonance imaging findings were typical for myocarditis, including regional dysfunction, late gadolinium enhancement, and elevated native T1 and T2.

Conclusions and Relevance

In this study, magnetic resonance imaging findings were found to be consistent with acute myocarditis in 7 patients; 4 of whom had preceding COVID-19 vaccination. Further investigation is needed to determine associations of COVID-19 vaccination and myocarditis.

Acute myocarditis associated with anti-COVID-19 vaccination

Novel anti-coronavirus disease 2019 mRNA vaccines are rapidly implemented worldwide. Therefore, attention should be given to potentially life-threatening adverse reactions. We report on three young male patients, who developed acute myocarditis 2 days after receiving the second dose of the BNT162b2 vaccine. Primary acute myocarditis was not previously reported in association with vaccines that do not include adjuvants. A high index of suspicion should be maintained in order to diagnose and treat patients who develop auto-inflammatory vaccine-related complications in a timely manner. Further research is required in order to explore the significance of this phenomenon and its underlying molecular mechanism.

Vaccination as a possible trigger for immune-mediated necrotising myopathy

Immune-mediated necrotising myopathy is a rare autoimmune myopathy characterised by severe progressive muscle weakness, elevated levels of creatine kinase (CK), and necrosis with minimal inflammatory cell infiltration on muscle biopsy. We report a case of a previously healthy 42-year-old woman who presented with progressive muscle weakness 2 weeks after immunisation for yellow fever, tetanus/diphtheria and hepatitis B. Her symptoms started from the lower limbs and progressed to the upper limbs and cervical region associated with dysphagia, making her wheelchair bound. Electromyography showed a myopathic pattern, with a CK level of 12.177 U/L (reference value: 26-190 U/L), and biceps brachial muscle biopsy confirmed necrosis and regeneration fibres. The immunoblot test was positive for antisignal recognition particle. She was successfully treated with prednisone (1 mg/kg/day). Although considered safe, vaccines may cause allergic reactions or trigger autoimmune disorders. Currently, a causal relationship between them cannot be established.

Rhabdomyolysis after recombinant zoster vaccination: a rare adverse reaction

We present a case report describing a potential rare adverse reaction of the recombinant zoster vaccination. This patient is a 60-year-old female who was admitted for severe rhabdomyolysis after receiving the vaccine. The patient’s symptoms and CPK improved with aggressive hydration over several days. The patient did not have any known or reported common risk factors for rhabdomyolysis and the Naranjo Score was used to determine the likelihood of an adverse drug reaction. This is a relevant case to discuss in order to make physicians aware of a possible rare and lethal adverse effect due to a common vaccination.

Influenza Vaccine-related Subacromial/Subdeltoid Bursitis: A Case Report

Serious side effects of vaccinations are not common, though rare complications can occur. We present a case of one such uncommon side effect, influenza vaccine-related subacromial/subdeltoid bursitis. A 72-year-old female presented with severe shoulder pain following influenza vaccination. The pain persisted for up to two months despite conservative measures, and MRI demonstrated moderate subacromial/subdeltoid bursitis. Vaccine-related shoulder dysfunction includes a range of pathology, from osteonecrosis to bursitis, which will be reviewed in this report. Recognition of infrequent vaccine-related musculoskeletal pathology is important to prevent delay of diagnosis.

Acute Fulminant Myocarditis Following Influenza Vaccination Requiring Extracorporeal Membrane Oxygenation

The inactivated influenza vaccination is generally safe with mostly mild side effects. We report a rare but fatal adverse event following influenza vaccination. A previously healthy 27-year-old woman who received the influenza vaccination 3 days before presenting to the emergency department had rapidly aggravating dyspnea and mental deterioration. She was diagnosed as having acute fulminant myocarditis with refractory cardiogenic shock, which was successfully managed with veno-arterial extracorporeal membrane oxygenation. The cardiac function of the patient recovered in 3 weeks.

A Young Male with Severe Myocarditis and Skeletal Muscle Myositis

A 34-year-old male presented with retrosternal chest pain, fatigue, shortness of breath, and a history of a previous episode of myocarditis four years prior. He had elevated troponin T, normal skeletal muscle enzymes, and negative inflammatory markers. Cardiac magnetic resonance imaging (MRI) confirmed active myocarditis with extensive myocardial fibrosis and normal left ventricular ejection fraction (LVEF). His myocarditis symptoms resolved with steroids and anti-inflammatory treatment, but on closer questioning, he reported a vague history of long-standing calf discomfort associated with episodes of stiffness, fatigue, and flu-like symptoms. MRI of the lower legs consequently demonstrated active myositis in the calf muscles. Immunomodulatory therapy was commenced with good effect. The patient is undergoing regular follow-up in both cardiology and rheumatology outpatient departments. Repeated MRI of the legs showed significant interval improvement in his skeletal muscle myositis, and repeat cardiac MRI demonstrated the resolution of myocarditis along with persistent stable extensive myocardial fibrosis and preserved LVEF. The patient has returned to full-time work.

Preclinical evaluation of the safety and pathogenicity of a live attenuated recombinant influenza A/H7N9 seed strain and corresponding MF59-adjuvanted split vaccine

Developing a safe and effective H7N9 influenza vaccine was initiated in early spring 2013, following human infections with a novel avian influenza A (H7N9) virus. In this study, a candidate H7N9 vaccine seed strain is produced using reverse genetics, with HA and NA derived from a human H7N9 virus and the remaining genes from the PR8 backbone virus which grows well in eggs. We verified that the virulence and transmissibility of the recombinant H7N9 vaccine seed strain were decreased as compared to wild-type H7N9 virus, to levels comparable with PR8. Using the seed virus, we produced a monovalent split influenza A (H7N9) MF59-adjuvanted vaccine that was immunogenic in mice. Our H7N9 vaccine is selected for clinical investigation and potential human use. To assess the safety of our H7N9 vaccine, we performed acute toxicity, repeated dose toxicity and active systemic anaphylaxis tests. Our results showed that, under the conditions used in this study, the NOEAL (no obvious adverse effect level) was 30 μg/0.5 mL.

Myocarditis: A Clinical Overview

PURPOSE OF REVIEW

In this paper we will review the modern diagnostic approach to patients with clinically suspected myocarditis as well as the treatment modalities and strategy in light of up-to-date clinical experience and scientific evidence.

RECENT FINDINGS

Rapidly expanding evidence suggests that myocardial inflammation is frequently underdiagnosed or overlooked in clinical practice, although new therapeutic options have been validated. Moreover, the available evidence suggests that subclinical cardiac involvement has negative prognostic impact on morbidity and mortality and should be actively investigated and adequately treated. Myocarditis represents a growing challenge for physicians, due to increased referral of patients for endomyocardial biopsy (EMB) or cardiac magnetic resonance (CMR), and requires a highly integrated management by a team of caring physicians.

Analysis of the immunogenicity and bioactivities of a split influenza A/H7N9 vaccine mixed with MF59 adjuvant in BALB/c mice

The H7N9 influenza virus caused significant mortality and morbidity in humans during an outbreak in China in 2013. A recombinant H7N9 influenza seed with hemagglutinin (HA) and neuraminidase (NA) gene segments from A/Zhejiang/DTID-ZJU01/2013(H7N9) and six internal protein gene segments from A/Puerto Rico/8/34(H1N1; PR8) were generated using reverse genetics. We sought to determine the immunogenic, protective properties, and mechanisms of a split avian influenza A/H7N9 vaccine mixed with MF59 adjuvant in comparison to vaccines that included other adjuvant. BALB/c mice were vaccinated with two doses of different amounts and combinations of this novel A/ZJU01/PR8/2013 split vaccine with adjuvant. Mice were subsequently challenged with A/Zhejiang/DTID-ZJU01/2013(H7N9) by intranasal inoculation. We verified that MF59 enhanced the HI, MN, and IgG antibody titers to influenza antigens. Compared with alum, MF59 could more potentially induce humoral immune responses and Th2 cytokine production after virus infection, while both MF59 and alum can slightly increase NK cell activity. This split H7N9 influenza vaccine with MF59 adjuvant could effectively induce antibody production and protect mice from H7N9 virus challenge. We have selected this vaccine for manufacture and future clinical studies to protect humans from H7N9 virus infection.