Tick-Borne Encephalitis Vaccine: Recommendations of the Advisory Committee on Immunization Practices, United States, 2023.

Tick-borne encephalitis (TBE) virus is focally endemic in parts of Europe and Asia. The virus is primarily transmitted to humans by the bites of infected: Ixodes species ticks but can also be acquired less frequently by alimentary transmission. Other rare modes of transmission include through breastfeeding, blood transfusion, solid organ transplantation, and slaughtering of viremic animals. TBE virus can cause acute neurologic disease, which usually results in hospitalization, often permanent neurologic or cognitive sequelae, and sometimes death. TBE virus infection is a risk for certain travelers and for laboratory workers who work with the virus. In August 2021, the Food and Drug Administration approved Ticovac TBE vaccine for use among persons aged ≥1 year. This report summarizes the epidemiology of and risks for infection with TBE virus, provides information on the immunogenicity and safety of TBE vaccine, and summarizes the recommendations of the Advisory Committee on Immunization Practices (ACIP) for use of TBE vaccine among U.S. travelers and laboratory workers.

Fatal Case of Heartland Virus Disease Acquired in the Mid-Atlantic Region, United States.

Heartland virus (HRTV) disease is an emerging tickborne illness in the midwestern and southern United States. We describe a reported fatal case of HRTV infection in the Maryland and Virginia region, states not widely recognized to have human HRTV disease cases. The range of HRTV could be expanding in the United States.

Improving community coverage of Japanese encephalitis vaccination: lessons learned from a mass campaign in Battambang Province, Cambodia.

A mass Japanese encephalitis (JE) immunization campaign for children aged 9 months through 12 years was conducted in 2013 in Battambang province, western Cambodia. Vaccinators working at almost 2,000 immunization posts in approximately 800 villages provided vaccinations to almost 310,000 children using one dose of Chengdu Institute of Biological Products' live, attenuated SA14-14-2 JE vaccine (CD-JEV), achieving a coverage rate of greater than 90%. Lessons learned, in general for mass vaccination campaigns and specifically for vaccination with CD-JEV, are described. These observations will be of benefit for public health officials and to help inform planning for future campaigns for JE or other vaccine-preventable diseases in Cambodia and elsewhere.

Risk Estimation of Sexual Transmission of Zika Virus-United States, 2016-2017.

BACKGROUND: Zika virus (ZIKV) can be transmitted sexually but the risk of sexual transmission remains unknown. Most evidence of sexual transmission is from partners of infected travelers returning from areas with ZIKV circulation. METHODS: We used data from the US national arboviral disease surveillance system on travel- and sexually acquired ZIKV disease cases during 2016-2017 to develop individual-level simulations for estimating risk of male-to-female, male-to-male, and female-to-male sexual transmission of ZIKV via vaginal and/or anal intercourse. We specified parametric distributions to characterize individual-level variability of parameters for ZIKV persistence and sexual behaviors. RESULTS: Using ZIKV RNA persistence in semen/vaginal fluids to approximate infectiousness duration, male-to-male transmission had the highest estimated probability (1.3% [95% confidence interval, CI, .4%-6.0%] per anal sex act), followed by male-to-female and female-to-male transmission (0.4% [95% CI, .3%-.6%] per vaginal/anal sex act and 0.1% [95% CI, 0%-.8%] per vaginal sex act, respectively). Models using viral isolation in semen vs RNA detection to approximate infectiousness duration predicted greater risk of sexual transmission. CONCLUSIONS: While likely insufficient to maintain sustained transmission, the estimated risk of ZIKV transmission through unprotected sex is not trivial and is especially important for pregnant women, as ZIKV infection can cause severe congenital disorders.

Case Series of Laboratory-Associated Zika Virus Disease, United States, 2016-2019.

Zika virus diagnostic testing and laboratory research increased considerably when Zika virus began spreading through the Americas in 2015, increasing the risk for potential Zika virus exposure of laboratory workers and biomedical researchers. We report 4 cases of laboratory-associated Zika virus disease in the United States during 2016-2019. Of these, 2 were associated with needlestick injuries; for the other 2 cases, the route of transmission was undetermined. In laboratories in which work with Zika virus is performed, good laboratory biosafety practices must be implemented and practiced to reduce the risk for infection among laboratory personnel.

Japanese Encephalitis Virus as Cause of Acute Encephalitis, Bhutan.

In 2011, Bhutan's Royal Centre for Disease Control began Japanese encephalitis (JE) surveillance at 5 sentinel hospitals throughout Bhutan. During 2011-2018, a total of 20 JE cases were detected, indicating JE virus causes encephalitis in Bhutan. Maintaining JE surveillance will help improve understanding of JE epidemiology in this country.

Japanese Encephalitis Vaccine: Recommendations of the Advisory Committee on Immunization Practices.

This report updates the 2010 recommendations from the CDC Advisory Committee on Immunization Practices (ACIP) regarding prevention of Japanese encephalitis (JE) among U.S. travelers and laboratory workers (Fischer M, Lindsey N, Staples JE, Hills S. Japanese encephalitis vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep 2010;59[No. RR-1]). The report summarizes the epidemiology of JE, describes the JE vaccine that is licensed and available in the United States, and provides recommendations for its use among travelers and laboratory workers.JE virus, a mosquitoborne flavivirus, is the most common vaccine-preventable cause of encephalitis in Asia. JE occurs throughout most of Asia and parts of the western Pacific. Approximately 20%-30% of patients die, and 30%-50% of survivors have neurologic, cognitive, or behavioral sequelae. No antiviral treatment is available.Inactivated Vero cell culture-derived JE vaccine (Ixiaro [JE-VC]) is the only JE vaccine that is licensed and available in the United States. In 2009, the U.S. Food and Drug Administration (FDA) licensed JE-VC for use in persons aged ≥17 years; in 2013, licensure was extended to include children aged ≥2 months.Most travelers to countries where the disease is endemic are at very low risk for JE. However, some travelers are at increased risk for infection on the basis of their travel plans. Factors that increase the risk for JE virus exposure include 1) traveling for a longer period; 2) travel during the JE virus transmission season; 3) spending time in rural areas; 4) participating in extensive outdoor activities; and 5) staying in accommodations without air conditioning, screens, or bed nets. All travelers to countries where JE is endemic should be advised to take precautions to avoid mosquito bites to reduce the risk for JE and other vectorborne diseases. For some persons who might be at increased risk for JE, the vaccine can further reduce the risk for infection. The decision about whether to vaccinate should be individualized and consider the 1) risks related to the specific travel itinerary, 2) likelihood of future travel to countries where JE is endemic, 3) high morbidity and mortality of JE, 4) availability of an effective vaccine, 5) possibility (but low probability) of serious adverse events after vaccination, and 6) the traveler's personal perception and tolerance of risk.JE vaccine is recommended for persons moving to a JE-endemic country to take up residence, longer-term (e.g., ≥1 month) travelers to JE-endemic areas, and frequent travelers to JE-endemic areas. JE vaccine also should be considered for shorter-term (e.g., <1 month) travelers with an increased risk for JE on the basis of planned travel duration, season, location, activities, and accommodations and for travelers to JE-endemic areas who are uncertain about their specific travel duration, destinations, or activities. JE vaccine is not recommended for travelers with very low-risk itineraries, such as shorter-term travel limited to urban areas or outside of a well-defined JE virus transmission season.

Screening for SARS-CoV-2 Infection Within a Psychiatric Hospital and Considerations for Limiting Transmission Within Residential Psychiatric Facilities - Wyoming, 2020.

In the United States, approximately 180,000 patients receive mental health services each day at approximately 4,000 inpatient and residential psychiatric facilities (1). SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19), can spread rapidly within congregate residential settings (2-4), including psychiatric facilities. On April 13, 2020, two patients were transferred to Wyoming's state psychiatric hospital from a private psychiatric hospital that had confirmed COVID-19 cases among its residents and staff members (5). Although both patients were asymptomatic at the time of transfer and one had a negative test result for SARS-CoV-2 at the originating facility, they were both isolated and received testing upon arrival at the state facility. On April 16, 2020, the test results indicated that both patients had SARS-CoV-2 infection. In response, the state hospital implemented expanded COVID-19 infection prevention and control (IPC) procedures (e.g., enhanced screening, testing, and management of new patient admissions) and adapted some standard IPC measures to facilitate implementation within the psychiatric patient population (e.g., use of modified face coverings). To assess the likely effectiveness of these procedures and determine SARS-CoV-2 infection prevalence among patients and health care personnel (HCP) (6) at the state hospital, a point prevalence survey was conducted. On May 1, 2020, 18 days after the patients' arrival, 46 (61%) of 76 patients and 171 (61%) of 282 HCP had nasopharyngeal swabs collected and tested for SARS-CoV-2 RNA by reverse transcription-polymerase chain reaction. All patients and HCP who received testing had negative test results, suggesting that the hospital's expanded IPC strategies might have been effective in preventing the introduction and spread of SARS-CoV-2 infection within the facility. In congregate residential settings, prompt identification of COVID-19 cases and application of strong IPC procedures are critical to ensuring the protection of other patients and staff members. Although standard guidance exists for other congregate facilities (7) and for HCP in general (8), modifications and nonstandard solutions might be needed to account for the specific needs of psychiatric facilities, their patients, and staff members.

Ability To Serologically Confirm Recent Zika Virus Infection in Areas with Varying Past Incidence of Dengue Virus Infection in the United States and U.S. Territories in 2016.

Cross-reactivity within flavivirus antibody assays, produced by shared epitopes in the envelope proteins, can complicate the serological diagnosis of Zika virus (ZIKAV) infection. We assessed the utility of the plaque reduction neutralization test (PRNT) to confirm recent ZIKAV infections and rule out misleading positive immunoglobulin M (IgM) results in areas with various levels of past dengue virus (DENV) infection incidence. We reviewed PRNT results of sera collected for diagnosis of ZIKAV infection from 1 January through 31 August 2016 with positive ZIKAV IgM results, and ZIKAV and DENV PRNTs were performed. PRNT result interpretations included ZIKAV, unspecified flavivirus, DENV infection, or negative. For this analysis, ZIKAV IgM was considered false positive for samples interpreted as a DENV infection or negative. In U.S. states, 208 (27%) of 759 IgM-positive results were confirmed to be ZIKAV compared to 11 (21%) of 52 in the U.S. Virgin Islands (USVI), 15 (15%) of 103 in American Samoa, and 13 (11%) of 123 in Puerto Rico. In American Samoa and Puerto Rico, more than 80% of IgM-positive results were unspecified flavivirus infections. The false-positivity rate was 27% in U.S. states, 18% in the USVI, 2% in American Samoa, and 6% in Puerto Rico. In U.S. states, the PRNT provided a virus-specific diagnosis or ruled out infection in the majority of IgM-positive samples. Almost a third of ZIKAV IgM-positive results were not confirmed; therefore, providers and patients must understand that IgM results are preliminary. In territories with historically higher rates of DENV transmission, the PRNT usually could not differentiate between ZIKAV and DENV infections.

Zika virus as a sexually transmitted pathogen.

PURPOSE OF REVIEW: Zika virus has recently emerged from an obscure mosquito-borne pathogen to an international public health concern. It is the first viral agent newly demonstrated to cause birth defects in several decades, and it is the only arbovirus now known to be transmitted sexually. The purpose of this review is to provide an overview of current understanding of sexual transmission of Zika virus and its possible clinical and public health consequences. RECENT FINDINGS: Sexual transmission of Zika virus has been reported from at least 13 countries without simultaneous mosquito-borne transmission; it is undoubtedly also occurring in countries with active arthropod transmission. Most published cases involve transmission from symptomatically infected men to women partners. Nevertheless, transmission from a symptomatic man to another man, from a symptomatic woman to a man, and from an asymptomatic man to a woman has also been reported. Sexual transmission has occurred before symptom onset, during illness, and after resolution of the source partner's symptoms. With the exception of a woman who developed symptomatic infection 44 days after onset of her husband's illness, nearly all instances reported to date have occurred within 20 days of the source partner's illness. Zika virus RNA has been detected in semen, saliva, blood, urine, and vaginal and cervical secretions; the length of time during which RNA can be detected varies widely across different body fluids but is especially lengthy in semen. Although semen has been found to contain ZIKV RNA for more than 180 days after illness onset, only a small proportion of samples with detectable RNA yield replicative virus whenever cultured. SUMMARY: Public health agencies have promulgated interim recommendations to prevent sexual transmission of Zika virus; however, much remains unknown regarding the duration of contagiousness and risk factors for transmission. Given the risk for birth defects, the greatest concern is for transmission of the virus to women who are pregnant or attempting to become pregnant. To prevent sexual transmission in general, couples are advised to use condoms or not have sex for at least 6 months from the start of the male partner's symptoms or the date he was diagnosed with Zika or after he has returned from an area with risk of ZIKV infection. Women who have symptomatic ZIKV infection or have traveled to an area of risk are advised to use condoms or avoid sex for 8 weeks from the start of the woman's symptoms or the date she was diagnosed with Zika or after the woman returns from the area of risk.

West Nile Virus and Other Nationally Notifiable Arboviral Diseases - United States, 2017.

Arthropodborne viruses (arboviruses) are transmitted to humans primarily through the bites of infected mosquitoes or ticks. West Nile virus (WNV) is the leading cause of domestically acquired arboviral disease in the continental United States (1). Other arboviruses, including Jamestown Canyon, La Crosse, Powassan, St. Louis encephalitis, and eastern equine encephalitis viruses, cause sporadic cases of disease and occasional outbreaks. This report summarizes surveillance data reported to CDC from U.S. states in 2017 for nationally notifiable arboviruses. It excludes dengue, chikungunya, and Zika viruses because, in the continental United States, these viruses are acquired primarily through travel. In 2017, 48 states and the District of Columbia (DC) reported 2,291 cases of domestic arboviral disease, including 2,097 (92%) WNV disease cases. Among the WNV disease cases, 1,425 (68%) were classified as neuroinvasive disease (e.g., meningitis, encephalitis, or acute flaccid paralysis), for a national rate of 0.44 cases per 100,000 population. More Jamestown Canyon and Powassan virus disease cases were reported in 2017 than in any previous year. Because arboviral diseases continue to cause serious illness, maintaining surveillance is important to direct and promote prevention activities.

Update: Interim Guidance for Preconception Counseling and Prevention of Sexual Transmission of Zika Virus for Men with Possible Zika Virus Exposure - United States, August 2018.

Zika virus infection can occur as a result of mosquitoborne or sexual transmission of the virus. Infection during pregnancy is a cause of fetal brain abnormalities and other serious birth defects (1,2). CDC has updated the interim guidance for men with possible Zika virus exposure who 1) are planning to conceive with their partner, or 2) want to prevent sexual transmission of Zika virus at any time (3). CDC now recommends that men with possible Zika virus exposure who are planning to conceive with their partner wait for at least 3 months after symptom onset (if symptomatic) or their last possible Zika virus exposure (if asymptomatic) before engaging in unprotected sex. CDC now also recommends that for couples who are not trying to conceive, men can consider using condoms or abstaining from sex for at least 3 months after symptom onset (if symptomatic) or their last possible Zika virus exposure (if asymptomatic) to minimize their risk for sexual transmission of Zika virus. All other guidance for Zika virus remains unchanged. The definition of possible Zika virus exposure remains unchanged and includes travel to or residence in an area with risk for Zika virus transmission (https://wwwnc.cdc.gov/travel/page/world-map-areas-with-zika) or sex without a condom with a partner who traveled to or lives in an area with risk for Zika virus transmission. CDC will continue to update recommendations as new information becomes available.

Update: Noncongenital Zika Virus Disease Cases - 50 U.S. States and the District of Columbia, 2016.

Zika virus is a flavivirus primarily transmitted to humans by Aedes aegypti mosquitoes (1). Zika virus infections also have been documented through intrauterine transmission resulting in congenital infection; intrapartum transmission from a viremic mother to her newborn; sexual transmission; blood transfusion; and laboratory exposure (1-3). Most Zika virus infections are asymptomatic or result in mild clinical illness, characterized by acute onset of fever, maculopapular rash, arthralgia, or nonpurulent conjunctivitis; Guillain-Barré syndrome, meningoencephalitis, and severe thrombocytopenia rarely have been associated with Zika virus infection (1). However, congenital Zika virus infection can result in fetal loss, microcephaly, and other birth defects (1,2). In 2016, a total of 5,168 noncongenital Zika virus disease cases were reported from U.S. states and the District of Columbia. Most cases (4,897, 95%) were in travelers returning from Zika virus-affected areas. A total of 224 (4%) cases were acquired through presumed local mosquitoborne transmission, and 47 (1%) were acquired by other routes. It is important that providers in the United States continue to test symptomatic patients who live in or recently traveled to areas with ongoing Zika virus transmission or had unprotected sex with someone who lives in or traveled to those areas. All pregnant women and their partners should take measures to prevent Zika virus infection during pregnancy. A list of affected areas and specific recommendations on how to prevent Zika virus infection during pregnancy are available at https://www.cdc.gov/pregnancy/zika/protect-yourself.html.

Breast milk transmission of flaviviruses in the context of Zika virus: A systematic review.

BACKGROUND: Since the Zika virus epidemic in the Americas began in 2015, Zika virus transmission has occurred throughout the Americas. However, limited information exists regarding possible risks of transmission of Zika virus and other flaviviruses through breast feeding and human milk. We conducted a systematic review of the evidence regarding flaviviruses detection in and transmission through milk, specifically regarding Zika virus, Japanese encephalitis virus, tick-borne encephalitis virus, Powassan virus, West Nile virus, dengue virus, and yellow fever virus. METHODS: Medline, Embase, Global Health, CINAHL, Cochrane Library, Scopus, Popline, Virtual Health Library, and WorldCat were searched through June 2017. Two authors independently screened potential studies for inclusion and extracted data. Human and nonhuman (animal) studies describing: 1) confirmed or suspected cases of mother-to-child transmission through milk; or 2) the presence of flavivirus genomic material in milk. RESULTS: Seventeen studies were included, four animal models and thirteen observational studies. Dengue virus, West Nile virus, and Zika virus viral ribonucleic acid was detected in human milk, including infectious Zika virus and dengue virus viral particles. Human breast-feeding transmission was confirmed for only yellow fever virus. There was evidence of milk-related transmission of dengue virus, Powassan virus, and West Nile virus in animal studies. CONCLUSIONS: Because the health advantages of breast feeding are considered greater than the potential risk of transmission, the World Health Organization recommends that mothers with possible or confirmed Zika virus infection or exposure continue to breast feed. This review did not identify any data that might alter this recommendation.

Epidemiology of Zika Virus Infection.

Long known to be endemic in Africa and Southeast Asia and a rare cause of acute febrile illness, Zika virus (ZIKAV) arose from obscurity when an Asian genotype ZIKAV caused an outbreak of mild febrile illness in 2007 in Yap State, Federated States of Micronesia. Subsequent viral spread in the Pacific led to a large outbreak in French Polynesia commencing in 2013. After its recognition in the Americas through March 2017, the Pan American Health Organization has received reports of >750000 suspected and laboratory-confirmed cases of autochthonous ZIKAV transmission. Outbreaks in most countries in the Americas peaked in early to mid-2016. Increased surveillance in several Southeast Asian counties has led to increased case recognition, including an outbreak in Singapore, and the first reports of birth defects linked to ZIKAV in the region. As of April 2017, the World Health Organization reported 84 countries or territories with current or previous ZIKAV transmission.

Modes of Transmission of Zika Virus.

For >60 years, Zika virus (ZIKV) has been recognized as an arthropod-borne virus with Aedes species mosquitoes as the primary vector. However in the past 10 years, multiple alternative routes of ZIKV transmission have been identified. We review the available data on vector and non-vector-borne modes of transmission and interventions undertaken, to date, to reduce the risk of human infection through these routes. Although much has been learned during the outbreak in the Americas on the underlying mechanisms and pathogenesis of non-vector-borne ZIKV infections, significant gaps remain in our understanding of the relative incidence of, and risk from, these modes compared to mosquito transmission. Additional research is urgently needed on the risk, pathogenesis, and effectiveness of measures to mitigate non-vector-borne ZIKV transmission.

Male-to-Female Sexual Transmission of Zika Virus-United States, January-April 2016.

We report on 9 cases of male-to-female sexual transmission of Zika virus in the United States occurring January-April 2016. This report summarizes new information about both timing of exposure and symptoms of sexually transmitted Zika virus disease, and results of semen testing for Zika virus from 2 male travelers.

Japanese Encephalitis Surveillance and Immunization - Asia and Western Pacific Regions, 2016.

Japanese encephalitis (JE) virus is the most important vaccine-preventable cause of encephalitis in the Asia-Pacific region. The World Health Organization (WHO) recommends integration of JE vaccination into national immunization schedules in all areas where the disease is a public health priority (1). This report updates a previous summary of JE surveillance and immunization programs in Asia and the Western Pacific in 2012 (2). Since 2012, funding for JE immunization has become available through the GAVI Alliance, three JE vaccines have been WHO-prequalified,* and an updated WHO JE vaccine position paper providing guidance on JE vaccines and vaccination strategies has been published (1). Data for this report were obtained from a survey of JE surveillance and immunization practices administered to health officials in countries with JE virus transmission risk, the 2015 WHO/United Nations Children's Fund Joint Reporting Form on Immunization, notes and reports from JE meetings held during 2014-2016, published literature, and websites. In 2016, 22 (92%) of 24 countries with JE virus transmission risk conducted JE surveillance, an increase from 18 (75%) countries in 2012, and 12 (50%) countries had a JE immunization program, compared with 11 (46%) countries in 2012. Strengthened JE surveillance, continued commitment, and adequate resources for JE vaccination should help maintain progress toward prevention and control of JE.

Establishing a Timeline to Discontinue Routine Testing of Asymptomatic Pregnant Women for Zika Virus Infection - American Samoa, 2016-2017.

The first patients with laboratory-confirmed cases of Zika virus disease in American Samoa had symptom onset in January 2016 (1). In response, the American Samoa Department of Health (ASDoH) implemented mosquito control measures (1), strategies to protect pregnant women (1), syndromic surveillance based on electronic health record (EHR) reports (1), Zika virus testing of persons with one or more signs or symptoms of Zika virus disease (fever, rash, arthralgia, or conjunctivitis) (1-3), and routine testing of all asymptomatic pregnant women in accordance with CDC guidance (2,3). All collected blood and urine specimens were shipped to the Hawaii Department of Health Laboratory for Zika virus testing and to CDC for confirmatory testing. Early in the response, collection and testing of specimens from pregnant women was prioritized over the collection from symptomatic nonpregnant patients because of limited testing and shipping capacity. The weekly numbers of suspected Zika virus disease cases declined from an average of six per week in January-February 2016 to one per week in May 2016. By August, the EHR-based syndromic surveillance (1) indicated a return to pre-outbreak levels. The last Zika virus disease case detected by real-time, reverse transcription-polymerase chain reaction (rRT-PCR) occurred in a patient who had symptom onset on June 19, 2016. In August 2016, ASDoH requested CDC support in assessing whether local transmission had been reduced or interrupted and in proposing a timeline for discontinuation of routine testing of asymptomatic pregnant women. An end date (October 15, 2016) was determined for active mosquito-borne transmission of Zika virus and a timeline was developed for discontinuation of routine screening of asymptomatic pregnant women in American Samoa (conception after December 10, 2016, with permissive testing for asymptomatic women who conceive through April 15, 2017).