SARS-CoV-2 Vaccination-Induced Transverse Myelitis

Central nervous system manifestations following vaccination against COVID-19

Coronavirus disease 2019 (COVID-19) vaccination has become the most effective countermeasure in the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. However, vaccination is associated with side effects. This narrative review focuses on central nervous system (CNS) manifestations following COVID-19 vaccination and provides a summary of the potential underlying mechanisms and methods of diagnosis and management of the vaccination-related CNS manifestations. Headache, myalgia, optic neuritis, seizure, multiple sclerosis, acute disseminated encephalomyelitis and encephalitis, delirium, acute transverse myelitis, and stroke have been reported after COVID-19 vaccination. Constant headache and myalgia are common manifestations that may necessitate further clinical investigation for stroke. To limit consequences, it is imperative to follow standard treatment protocols for each neurological disorder following COVID-19 vaccination. Immunosuppressive medication can be helpful in the treatment of seizures following vaccination since the immune response is involved in their etiology. Clinicians should be aware of the manifestations after COVID-19 vaccination to respond promptly and effectively. Clinical guidelines for the management of CNS manifestations following COVID-19 vaccination are in high demand and would be useful in each new SARS-CoV-2 variant pandemic.

A report on neurogenic bladder in COVID-19 vaccine-associated acute transverse myelitis

INTRODUCTION

Acute transverse myelitis (ATM) is a rare neurological complication of Coronavirus disease (COVID-19) vaccines. Various vaccines have been linked to ATM, such as non-replicating viral vectors, ribonucleic acid, and inactivated vaccines. An ATM case is presented here involving the BNT162b2 vaccine leading to asymmetrical incomplete paraplegia and neurogenic bladder.

CASE PRESENTATION

A 66-year-old male developed urinary retention one day after his second dose of the BNT162b2 vaccine, followed by rapidly progressing lower limb weakness. Clinical examination showed asymmetrical paraparesis, reduced sensation below the T8 level, including perianal sensation, and loss of ankle and anal reflexes. Laboratory tests were largely unremarkable, while the spine MRI revealed thickened conus medullaris with a mild increase in T2/STIR signal intensity and subtle enhancement post gadolinium. Following treatment with methylprednisolone, plasmapheresis, and immunoglobulin, and a rehabilitation program, the patient achieved good motor and sensory recovery, but the bladder dysfunction persisted. Single-channel cystometry indicated neurogenic detrusor underactivity and reduced bladder sensation, as evidenced by low-pressure and compliant bladder. The urethral sphincter appeared intact or overactive. The post-void residual urine was significant, necessitating prolonged intermittent catheterisation.

DISCUSSION

Bladder dysfunction due to the COVID-19 vaccine-associated ATM is not as commonly reported as motor or sensory deficits. To our knowledge, this is the first case to highlight a neurogenic bladder that necessitates prolonged intermittent catheterisation as a consequence of COVID-19 vaccine-associated ATM. This report highlights the rare complication of the neurogenic bladder resulting from the BNT162b2 vaccine. Early detection and treatment are crucial to prevent long-term complications.

COVID-19-induced gastrointestinal autonomic dysfunction: A systematic review

In recent years, because of the growing desire to improve the noninvasiveness and safety of tumor treatments, sonodynamic therapy has gradually become a popular research topic. However, due to the complexity of the therapeutic process, the relevant mechanisms have not yet been fully elucidated. One of the widely accepted possibilities involves the effect of reactive oxygen species. In this review, the mechanism of reactive oxygen species production by sonodynamic therapy (SDT) and ways to enhance the sonodynamic production of reactive oxygen species are reviewed. Then, the clinical application and limitations of SDT are discussed. In conclusion, current research on sonodynamic therapy should focus on the development of sonosensitizers that efficiently produce active oxygen, exhibit biological safety, and promote the clinical transformation of sonodynamic therapy.

COVID-19-induced gastrointestinal autonomic dysfunction: A systematic review

BACKGROUND

It is common for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection to occur in the gastrointestinal tract, which can present itself as an initial symptom. The severity of coronavirus disease 2019 (COVID-19) is often reflected in the prevalence of gastrointestinal symptoms. COVID-19 can damage the nerve supply to the digestive system, leading to gastrointestinal autonomic dysfunction. There is still much to learn about how COVID-19 affects the autonomic nervous system and the gastrointestinal tract.

AIM

To thoroughly explore the epidemiology and clinical aspects of COVID-19-induced gastrointestinal autonomic dysfunction, including its manifestations, potential mechanisms, diagnosis, differential diagnosis, impact on quality of life, prognosis, and management and prevention strategies.

METHODS

We conducted a thorough systematic search across various databases and performed an extensive literature review. Our review encompassed 113 studies published in English from January 2000 to April 18, 2023.

RESULTS

According to most of the literature, gastrointestinal autonomic dysfunction can seriously affect a patient's quality of life and ultimate prognosis. Numerous factors can influence gastrointestinal autonomic nervous functions. Studies have shown that SARS-CoV-2 has a well-documented affinity for both neural and gastrointestinal tissues, and the virus can produce various gastrointestinal symptoms by reaching neural tissues through different pathways. These symptoms include anorexia, dysgeusia, heartburn, belching, chest pain, regurgitation, vomiting, epigastric burn, diarrhea, abdominal pain, bloating, irregular bowel movements, and constipation. Diarrhea is the most prevalent symptom, followed by anorexia, nausea, vomiting, and abdominal pain. Although COVID-19 vaccination may rarely induce autonomic dysfunction and gastrointestinal symptoms, COVID-19-induced autonomic effects significantly impact the patient's condition, general health, prognosis, and quality of life. Early diagnosis and proper recognition are crucial for improving outcomes. It is important to consider the differential diagnosis, as these symptoms may be induced by diseases other than COVID-19-induced autonomic dysfunction. Treating this dysfunction can be a challenging task.

CONCLUSION

To ensure the best possible outcomes for COVID-19 patients, it is essential to take a multidisciplinary approach involving providing supportive care, treating the underlying infection, managing dysfunction, monitoring for complications, and offering nutritional support. Close monitoring of the patient's condition is crucial, and prompt intervention should be taken if necessary. Furthermore, conducting thorough research on the gastrointestinal autonomic dysfunction caused by COVID-19 is vital to manage it effectively.

A review of neurological side effects of COVID-19 vaccination

Following the COVID-19 virus epidemic, extensive, coordinated international research has led to the rapid development of effective vaccines. Although vaccines are now considered the best way to achieve collective safety and control mortality, due to the critical situation, these vaccines have been issued the emergency use licenses and some of their potential subsequence side effects have been overlooked. At the same time, there are many reports of side effects after getting a COVID-19 vaccine. According to these reports, vaccination can have an adverse event, especially on nervous system. The most important and common complications are cerebrovascular disorders including cerebral venous sinus thrombosis, transient ischemic attack, intracerebral hemorrhage, ischemic stroke, and demyelinating disorders including transverse myelitis, first manifestation of MS, and neuromyelitis optica. These effects are often acute and transient, but they can be severe and even fatal in a few cases. Herein, we have provided a comprehensive review of documents reporting neurological side effects of COVID-19 vaccines in international databases from 2020 to 2022 and discussed neurological disorders possibly caused by vaccination.

Cervical Transverse Myelitis Following COVID-19 Vaccination

Various COVID-19 vaccines are associated with numerous adverse side effects. Associations between vaccinations and neurological disorders, such as transverse myelitis, stroke, Bell's palsy, acute disseminated encephalomyelitis, and Guillain-Barré syndrome, have been reported. A 27-year-old Japanese woman presented with paresthesia four days after receiving a second dose of the COVID-19 vaccine. One month after vaccination, she started to feel left lower limb weakness, and her symptoms almost improved after two steroid pulse therapies. Spinal cord tumor biopsy could potentially help make a definitive diagnosis in clinical situations. However, it is very important to review the patient's medical history, including vaccinations received, before performing a direct spinal cord biopsy, which is invasive and does not guarantee a definitive diagnosis.

Longitudinally extensive transverse myelitis after Covid-19 vaccination: case report and review of literature

Mass vaccination has been the main policy to overcome the Covid-19 pandemic. Several vaccines have been approved by the World Health Organization. With growing vaccination, safety concerns and adverse events that need prompt evaluation are also emerging. Herein, we report a case of a healthy woman with longitudinally extensive transverse myelitis after vaccination with the AstraZeneca vaccine. The patient was successfully treated after ruling out all the possible causes.

CNS inflammatory demyelinating events after COVID-19 vaccines: A case series and systematic review

BACKGROUND

Vaccinations provided the most effective tool to fight the SARS-CoV-2 pandemic. It is now well established that COVID-19 vaccines are safe for the general population; however, some cases of rare adverse events following immunization have been described, including CNS Inflammatory Demyelinating Events (CIDEs). Although observational studies are showing that these events are rare and vaccines' benefits highly outweigh the risks, collecting and characterizing post-COVID-19 vaccine CIDEs might be relevant to single out potential risk factors and suggest possible underlying mechanisms.

METHODS

Here we describe six CIDEs, including two acute transverse myelitis (ATM), three multiple sclerosis (MS), and one neuromyelitis optica spectrum disorder (NMOSD), occurring between 8 and 35 days from a COVID-19 vaccine. Moreover, we performed a systematic literature search of post-COVID-19 vaccines CIDEs, including ATM, ADEM, MS, and NMOSD/MOGAD, published worldwide between December 2020 and December 2021, during 1 year of the vaccination campaign. Clinical/MRI and CSF/serum characteristics were extracted from reviewed studies and pooled-analyzed.

RESULTS

Forty-nine studies were included in the systematic review, reporting a total amount of 85 CIDEs. Considering our additional six cases, 91 CIDEs were summarized, including 24 ATM, 11 ADEM, 47 MS, and nine NMOSD/MOGAD. Overall, CIDEs occurred after both mRNA (n = 46), adenoviral-vectored (n = 37), and inactivated vaccines (n = 8). Adenoviral-vectored vaccines accounted for the majority of ADEM (55%) and NMOSD/MOGAD (56%), while mRNA vaccines were more frequent in MS new diagnoses (87%) and relapses (56%). Age was heterogeneous (19-88) and the female sex was prevalent. Time from vaccine to symptoms onset was notably variable: ADEM and NMOSD/MOGAD had a longer median time of onset (12.5 and 10 days) compared to ATM and MS (6 and 7 days) and further timing differences were observed between events following different vaccine types, with ATM and MS after mRNA-vaccines occurring earlier than those following adenoviral-vectored ones.

CONCLUSION

Both the prevalence of vaccine types for certain CIDEs and the heterogeneity in time of onset suggest that different mechanisms-with distinct dynamic/kinetic-might underly these events. While epidemiological studies have assessed the safety of COVID-19 vaccines, descriptions and pooled analyses of sporadic cases may still be valuable to gain insights into CIDE's pathophysiology.

Do we miss rare adverse events induced by COVID-19 vaccination?

Although severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has caused many complications, the invention of coronavirus disease 2019 (COVID-19) vaccines has also brought about several adverse events, from common side effects to unexpected and rare ones. Common vaccine-related adverse reactions manifest locally or systematically following any vaccine, including COVID-19 vaccines. Specific side effects, known as adverse events of particular interest (AESI), are unusual and need more evaluation. Here, we discuss some of the most critical rare adverse events of COVID-19 vaccines.

Transverse myelitis following SARS-CoV-2 vaccination: a pharmacoepidemiological study in the World Health Organization's database

Background

Transverse myelitis (TM) has recently been associated by health authorities with Ad26.COV2.S (Janssen/Johnson & Johnson), one of the 5 US Food and Drug Administration (FDA) or European Medicines Agency (EMA) labeled severe acute respiratory syndrome‐coronavirus 2 (SARS‐CoV‐2) vaccines. It is unknown whether a similar association exists for the other FDA or EMA labeled SARS‐CoV‐2 vaccines (BNT162b2 [Pfizer/BioNTech], mRNA‐1273 [Moderna], ChAdOx1nCov‐19 [Oxford–AstraZeneca], and NVX‐CoV2373 [Novavax]). This study aimed to evaluate the association between SARS‐CoV‐2 vaccine class and TM.

Methods

This observational, cross‐sectional, pharmacovigilance cohort study examined individual case safety reports from VigiBase, the World Health Organization's pharmacovigilance database. We first conducted a disproportionality analysis with the information component (IC) using the reports of TM that occurred within 28 days following exposure to the FDA or EMA labeled SARS‐CoV‐2 vaccines, from December 1, 2020 (first adverse event related to a SARS‐CoV‐2 vaccine) to March 27, 2022. Second, we analyzed the clinical features of SARS‐CoV‐2 vaccine‐associated TM cases reported in VigiBase.

Results

TM was significantly associated both with the messenger ribonucleic acid (mRNA)‐based (n = 364; IC₀₂₅ = 0.62) and vector‐based (n = 136; IC₀₂₅ = 0.52) SARS‐CoV‐2 vaccines that are authorized by the FDA or the EMA.

Conclusions

Findings from this observational, cross‐sectional pharmacovigilance study showed that mRNA‐based and vector‐based FDA/EMA labeled SARS‐CoV‐2 vaccines can be associated with TM. However, because TM remains a rare event, with a previously reported rate of 0.28 cases per 1 million vaccine doses, the risk–benefit ratio in favor of vaccination against SARS‐CoV‐2 virus remains unchallenged. Rather, this study suggests that clinicians should consider the diagnosis of TM in patients presenting with early signs of spinal cord dysfunction after SARS‐CoV‐2 vaccination. ANN NEUROL 2022

Safety of COVID-19 Vaccines: Spotlight on Neurological Complications

The COVID-19 pandemic has led to unprecedented demand on the global healthcare system. Remarkably, at the end of 2021, COVID-19 vaccines received approvals for human use in several countries worldwide. Since then, a solid base for response in the fight against the virus has been placed. COVID-19 vaccines have been shown to be safe and effective drugs. Nevertheless, all kinds of vaccines may be associated with the possible appearance of neurological complications, and COVID-19 vaccines are not free from neurological side effects. Neurological complications of COVID-19 vaccination are usually mild, short-duration, and self-limiting. However, severe and unexpected post-vaccination complications are rare but possible events. They include the Guillain-Barré syndrome, facial palsy, other neuropathies, encephalitis, meningitis, myelitis, autoimmune disorders, and cerebrovascular events. The fear of severe or fatal neurological complications fed the "vaccine hesitancy" phenomenon, posing a vital communication challenge between the scientific community and public opinion. This review aims to collect and discuss the frequency, management, and outcome of reported neurological complications of COVID-19 vaccines after eighteen months of the World Health Organization's approval of COVID-19 vaccination, providing an overview of safety and concerns related to the most potent weapon against the SARS-CoV-2.

Extensive Longitudinal Transverse Myelitis Temporally Related to the Use of AZD1222, AstraZeneca COVID-19 Vaccine: Cerebrospinal Fluid Analysis and Recent Data Review

While mass immunization against coronavirus disease 2019 (COVID-19) rolls out around the globe, safety concerns and adverse events that need prompt evaluation are also emerging. Neurological complications such as transverse myelitis raise concerns as cases were observed in clinical trials. Cerebrospinal fluid analysis is routine in these cases and the characteristics of the abnormalities found are of great help not only in establishing the diagnosis but also in understanding this rare condition. We present a case of extensive longitudinal transverse myelitis after vaccination with AZD1222, AstraZeneca COVID-19 vaccine, which was the first case reported in Brazil. The abnormalities found in the study of the cerebrospinal fluid in our case are reported and discussed using data from recent publications.

Refractory Longitudinally Extensive Transverse Myelitis after Severe Acute Respiratory Syndrome Coronavirus 2 Vaccination in a Japanese Man

Vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been developed and administered worldwide. There have been reports of neurological adverse events following immunization (AEFIs). We herein report a case of refractory longitudinally extensive transverse myelitis in a 75-year-old Japanese man following the first dose of the BNT162b2 vaccine. The patient developed total sensory loss below the umbilicus and complete paralysis in both legs. Although he was treated with steroid therapy and plasma exchange, his recovery was limited, and severe sequelae remained. Further studies, including large epidemiological studies, are required to understand the association between SARS-CoV-2 vaccines and neurological AEFI.

Interstitial Lung Disease and Transverse Myelitis: A Possible Complication of COVID-19 Vaccine

The clinical impact of the severe acute respiratory syndrome 2 (SARS-CoV-2) pandemic is growing, and vaccine-associated complications are becoming more evident. Although global vaccination against coronavirus disease 19 (COVID-19) is an outstanding accomplishment, safety concerns and adverse outcomes are also emerging that need to be addressed promptly. The most reported side effects of the COVID-19 vaccine include fever, myalgia, headache, and injection site reactions. Acute transverse myelitis (ATM) and interstitial lung disease (ILD) following the CoronaVac vaccine are rarely reported. We report a case of ILD followed by acute myelopathy in a female who presented with dyspnea, cough, and fever after the second dose of the COVID-19 vaccine. On the third day of admission, she developed paresthesia and bilateral upper and lower limb weakness. She was diagnosed with ILD and ATM due to the COVID-19 vaccine based on imaging and detailed investigations after ruling out all possible causes. Her neurological and respiratory manifestations improved gradually after starting intravenous methylprednisolone.

Reversible radiculomyelitis after ChAdOx1 nCoV-19 vaccination

Adverse events occurring after SARS-CoV-2 vaccination have been reported and are the subject of ongoing research. We present the case of a young woman with fully reversible radiculomyelitis, which happened after the first dose of the ChAdOx1 nCOVID-19 vaccine. A previously healthy woman in her 20s presented with a subacute onset of legs’ weakness and sensory disturbances, urinary dysfunction and cramping pain after receiving the first dose of the ChAdOx1 nCoV-19 vaccine. A diagnostic workup led to the diagnosis of inflammatory radiculomyelitis. Her clinical status improved, with complete recovery after a few months. The case described a reversible radiculomyelitis associated with the ChAdOx1 nCOVID-19 vaccine. The clinical picture and evolution supported the diagnosis. No other identifiable causes of myelopathy were found. Our patient showed clinically moderate symptoms and signs, showing good recovery. The post-vaccine inflammatory radiculomyelitis is a rare side effect of the anti-COVID-19 vaccination, and it should not discourage the SARS-CoV-2 vaccination programme.

Neurological side effects of SARS-CoV-2 vaccinations

SARS-CoV-2 and adverse reactions to SARS-CoV-2 vaccinations show a tropism for neuronal structures and tissues. This narrative review was conducted to collect and discuss published data about neurological side effects of SARS-CoV-2 vaccines in order to discover type, frequency, treatment, and outcome of these side effects. The most frequent neurological side effects of SARS-CoV-2 vaccines are headache, Guillain-Barre syndrome (GBS), venous sinus thrombosis (VST), and transverse myelitis. Other neurological side effects occur in a much lower frequency. Neurological side effects occur with any of the approved vaccines but VST particularly occurs after vaccination with vector-based vaccines. Treatment of these side effects is not at variance from similar conditions due to other causes. The worst outcome of these side effects is associated with VST, why it should not be missed and treated appropriately in due time. In conclusion, safety concerns against SARS-CoV-2 vaccines are backed by an increasing number of studies reporting neurological side effects. The most frequent of them are headache, GBS, VST, and transverse myelitis. Healthcare professionals, particularly neurologists involved in the management of patients having undergone SARS-CoV-2 vaccinations, should be aware of these side effects and should stay vigilant to recognize them early and treat them adequately.

Spectrum of neurological complications following COVID-19 vaccination

COVID-19 vaccines have brought us a ray of hope to effectively fight against deadly pandemic of COVID-19 and hope to save lives. Many vaccines have been granted emergency use authorizations by many countries. Post-authorization, a wide spectrum of neurological complications is continuously being reported following COVID-19 vaccination. Neurological adverse events following vaccination are generally mild and transient, like fever and chills, headache, fatigue, myalgia and arthralgia, or local injection site effects like swelling, redness, or pain. The most devastating neurological post-vaccination complication is cerebral venous sinus thrombosis. Cerebral venous sinus is frequently reported in females of childbearing age, generally following adenovector-based vaccination. Another major neurological complication of concern is Bell's palsy that was reported dominantly following mRNA vaccine administration. Acute transverse myelitis, acute disseminated encephalomyelitis, and acute demyelinating polyneuropathy are other unexpected neurological adverse events that occur as result of phenomenon of molecular mimicry. Reactivation of herpes zoster in many persons, following administration of mRNA vaccines, has been also recorded. Considering the enormity of recent COVID-19-vaccinated population, the number of serious neurological events is miniscule. Large collaborative prospective studies are needed to prove or disprove causal association between vaccine and neurological adverse events occurring vaccination.

Longitudinally extensive transverse myelitis following ChAdOx1 nCoV-19 vaccine

Transverse myelitis (TM) has been reported in association with various vaccinations. Herein we describe a case of longitudinally extensive transverse myelitis (LETM) associated with vaccination with ChAdOx1 nCoV-19 (COVISHIELD) vaccine. A 59-year-old woman with no prior co-morbidities presented with lower extremity numbness, weakness, acute urinary retention, and constipation. Numbness gradually extended up to the lower costal margin with band like sensation. She had received the vaccine 5 days prior to the onset of the symptoms. Extensive diagnostic evaluation effectively ruled out causes other than vaccination-associated transverse myelitis. Following treatment with intravenous methylprednisolone, the patient made a significant recovery. TM may be associated with vaccination against the novel ChAdOx1 nCoV-19 vaccine and we believe this to be the first report from India of LETM associated with this vaccine.

Acute autoimmune transverse myelitis following COVID-19 vaccination: A case report

RATIONALE

Transverse myelitis is an infectious or noninfectious inflammatory spinal cord syndrome. We report a rare case of transverse myelitis following vaccination against COVID-19.

PATIENT CONCERNS

A 70-year-old male presented with progressive sensorimotor dysfunction of the bilateral lower limbs 7 days after receiving the mRNA-1273 vaccine against COVID-19. Spinal magnetic resonance imaging revealed intramedullary lesions with gadolinium enhancement on the Th1/2 and Th5/6 vertebral levels. Cerebrospinal fluid (CSF) testing showed a mildly increased level of total protein and positive oligoclonal bands (OCB).

DIAGNOSIS

The patient was diagnosed with acute transverse myelitis.

INTERVENTION

The patient received 5 days of intravenous methylprednisolone pulse (1000 mg/day) followed by oral prednisolone (30 mg/day with gradual tapering).

OUTCOMES

The patient fully recovered from muscle weakness of the lower limbs. He was discharged from our hospital and able to independently walk without unsteadiness.

LESSON

This is a rare case of transverse myelitis following COVID-19 vaccination. Positive OCB in CSF in the present case highlights the possibility of autoimmune processes, including polyclonal activation of B lymphocytes, following vaccination.

Coronavirus disease 2019 (Covid-19) vaccination recommendations in special populations and patients with existing comorbidities

Vaccination against severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) is a crucial step in ending the current worldwide pandemic. However, several particularly vulnerable groups in the population were not included in sufficient numbers in coronavirus disease 2019 (Covid‐19) vaccine trials. Therefore, as science advances, the advice for vaccinating these special populations against Covid‐19 will continue to evolve. This focused review provides the latest recommendations and considerations for these special populations (i.e., patients with rheumatologic and autoimmune disorders, cancer, transplant recipients, chronic liver diseases, end‐stage renal disease, neurologic disorders, psychiatric disorders, diabetes mellitus, obesity, cardiovascular diseases, chronic obstructive pulmonary disease, human immunodeficiency virus, current smokers, pregnant and breastfeeding women, the elderly, children, and patients with allergic reactions) using the currently available research evidence.

Acute Transverse Myelitis after COVID-19 Vaccination

The adverse effects of the COVID-19 vaccine have been discovered as the rapid application of the vaccines continues. Neurological complications such as transverse myelitis raise concerns as cases were observed in clinical trials. Transverse myelitis is a rare immune-mediated disease with spinal cord neural injury, resulting in neurological deficits in the motor, sensory, and autonomic system. Vaccine-related transverse myelitis is even rarer. We present a case of acute transverse myelitis after vaccination against COVID-19 with the ChAdOx1 nCOV-19 vaccine (AZD1222), which was the first case reported in Taiwan. Although it rarely occurs, post-vaccination neurological complications should not be ignored. As the pandemic of SARS-CoV-2 continues to spread and concern about vaccination efficacy and safety rises, heterologous vaccination were implemented in health public policy in several countries. A literature review of several clinical trials shows promising effects of mix-and-match vaccination. Further study on different combinations of vaccines can be expected.