select search filters
briefings
roundups & rapid reactions
Fiona fox's blog
Scientists comment on a Nipah virus outbreak in India.
Prof Piero Olliaro, Professor of Poverty Related Infectious Diseases, University of Oxford, said:
What is Nipah virus?
“Nipah virus is a zoonotic (infecting animals) virus. It can occasionally infect humans, in which case it is highly lethal, with mortality averaging 70% (see our paper https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247(25)00223-X/fulltext) Nipah virus outbreaks are typically small and localised.
How is it spread?
“Nipah virus spreads to humans through several routes. The virus is naturally carried by fruit bats (Pteropus species), and transmission can occur when people consume food contaminated with bat saliva or urine, such as raw date palm sap, or have direct contact with infected bats. In some outbreaks, domestic animals, most notably pigs, have acted as intermediate hosts, transmitting the virus to humans through close contact. Nipah virus can also spread from person to person, particularly through close physical contact and exposure to respiratory secretions or other bodily fluids of an infected individual, most often within households or healthcare settings. However, the virus does not transmit easily between people, and sustained community-wide spread has not been observed, resulting in outbreaks that are typically small and localized.
Should we be especially worried about this outbreak?
“Based on available information, the current outbreak does not appear larger or more severe than previous Nipah outbreaks. Similar past outbreaks have involved small clusters with limited human-to-human transmission. Rapid public-health responses have so far helped contain spread.
“Based on what we currently know, there is a very low likelihood that this outbreak will cause a large international epidemic. It does not spread easily between people. Most transmission has been linked to close contact with infected bodily fluids, such as in households or healthcare settings, rather than sustained community spread.
“That said, Nipah remains a serious global health concern and is listed by the World Health Organization as a priority pathogen for research because of its wide natural host range (fruit bats), high mortality in humans, and lack of approved vaccines or treatments. These features, especially the absence of medical countermeasures and the potential for spillover from animals, mean that we must continue investing in surveillance, rapid diagnostics, and countermeasure development even though the virus does not currently exhibit the transmissibility needed to cause a pandemic.
What measures are being taken to contain the current outbreak?
“The best protection is avoiding known sources of infection. People should not consume raw date palm sap, avoid half-eaten or bat-bitten fruit, wash and peel fruit before eating, and avoid contact with bats or sick animals. Good hand hygiene and avoiding close contact with infected individuals are also important.
In healthcare settings, strict infection-control measures, including patient isolation and appropriate use of personal protective equipment, are essential to limit human-to-human transmission.
“There is currently no specific cure for Nipah virus infection. Outbreaks are rare and unpredictable, making it challenging to conduct the clinical trials that are commonly needed to prove that a treatment works. Development is also slowed by operational challenges, limited high-containment laboratory capacity, no business case for industry, and delayed diagnosis due to the lack of rapid tests – so for now, treatment remains supportive (see our paper: (https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(23)00707-7/abstract ).
“However, progress has been made: several vaccine candidates have advanced through early testing, and the University of Oxford’s ChAdOx1 NipahB vaccine has entered Phase II trials in an at-risk region, with multiple other candidates progressing toward human testing. Additionally, a monoclonal antibody (MBP1F5) funded by CEPI is planned to begin clinical evaluation as a potential immediate protective tool, reflecting growing investment in medical countermeasures against this priority pathogen.”
Dr Kaja Abbas, Associate Professor of Infectious Disease Epidemiology and Dynamics at the London School of Hygiene & Tropical Medicine and Nagasaki University:
What is Nipah virus?
“Nipah virus is a zoonotic RNA virus first identified in 1999 that causes severe respiratory and neurological disease in humans, potentially progressing from fever and headache to acute encephalitis. Since 2001, sporadic but recurring outbreaks have occurred, especially in Bangladesh and India. In addition to zoonotic transmission from animals such as fruit bats to humans, human-to-human transmission and transmission from contaminated fruit products (such as date palm juice) to humans also occur.
What is the current situation regarding the outbreak?
“India’s health ministry has confirmed two cases in West Bengal, India, since December 2025 among healthcare workers, and traced contacts have tested negative for Nipah infection.
What measures are being taken to contain the current outbreak?
“To prevent international spread, countries such as Thailand and Nepal has initiated screening passengers from India at the point of entry through air or land, and other countries such as Kazakhstan has issued guidance through their health ministries to follow medical observation for 14 days upon arrival. General prevention focuses on good hygiene, proper ventilation, avoiding crowds and sick contacts, staying home when ill, seeking timely medical advice, and maintaining a healthy lifestyle to support immunity.
How unprecedented/precedented was this outbreak?
“Since 2001, sporadic but recurring outbreaks have occurred, especially in Bangladesh and India. In addition to zoonotic transmission from animals such as fruit bats to humans, human-to-human transmission, and transmission from contaminated fruit products (such as date palm juice) to humans also occur.
What is the risk to the public?
“The basic reproduction number of the Nipah virus is typically below 1, suggesting limited human-to-human transmission and a low likelihood of widespread pandemic spread.”
Prof Ian Jones, Professor of Virology, University of Reading, said:
“Nipah is a bat virus that causes occasional zoonotic outbreaks, most of which are associated with the seasonal consumption of foodstuffs contaminated by bat urine. Like other zoonotics such as Avian flu or Ebola, the case fatality rate is high, but the virus does not transmit effectively person to person. The at-risk groups are therefore close family members and the healthcare workers who treat the primary cases. The risk to the general public from Nipah is essentially nil as the virus has never shown any evidence of general spread. “
Dr Efstathios Giotis, Lecturer in Molecular Virology at University of Essex, said:
What is Nipah virus?
“Nipah virus is a relatively rare zoonotic infection that primarily originates in fruit bats and can occasionally pass to pigs and humans, either directly or through contaminated food. In some circumstances, it can spread between people, particularly during close contact in healthcare settings. Infection can be severe, affecting the lungs and brain, and there is currently no licensed vaccine or specific treatment.
What is the current situation regarding the outbreak?
“In West Bengal, health authorities have confirmed two Nipah cases following investigations at a private hospital in Barasat. Initial reports suggested a higher number, but further testing narrowed this to two primary cases. Some suspected infections involved healthcare workers, raising concerns about possible hospital-related transmission. There is no indication of wider community spread at this time.
What measures are being taken to contain the outbreak?
“Patients have been isolated in specialist infectious disease facilities, and stringent infection-control protocols have been reinforced in hospitals. Nearly 200 close contacts have been identified for monitoring, and surveillance has been expanded statewide to ensure rapid detection of any new cases.
How unprecedented is this outbreak?
“This event is not unusual in the context of Nipah virus. Similar, small-scale outbreaks have occurred previously in India, including in West Bengal and Kerala. As in past incidents, the number of cases remains limited, and the public-health response has been swift and targeted.
What is the risk to the public?
“For the general population, the risk remains low. Nipah virus does not spread easily and typically requires close, prolonged exposure to an infected person or specific animal-related routes. While vigilance is warranted, there is no evidence to suggest a broader public health threat at this stage.”
Prof Paul Hunter, Professor in Medicine, University of East Anglia (UEA), said:
“Nipah virus infection is a rare infectious disease but one that can pose a significant risk of death. The death rates vary between and have been as low as 9% or as high as 90% of known cases. However, up to about half of infections may not cause any symptoms. So, the mortality rates per infection may be lower than reported. The incubation period is usually about one to two weeks but can be longer.
“The infection usually spread from animals to humans either through direct contact or consumption of contaminated food. The primary source of infection is bats and people have been infected from consumption of fruit or fruit products – such as raw date palm juice – contaminated with urine or saliva from infected fruit bats. However, the first outbreak was associated with contact with infected pigs. Those pigs probably got infected from bats.
“Person-to-person spread does occur but less commonly. Though, spread from infected patients to their health professionals is a particular concern.
“Outbreaks have been most years in Southeast Asia since the first one was identified in Malaysia in 1998/99. Most outbreaks have been reported from Bangladesh. This is not the first time that outbreaks have been identified in West Bengal.
“It is not clear to me how many cases have been linked to the current outbreak. Recent reports suggest only two confirmed cases, both in health care workers. So, the assumption is that they contacted their infection from an infected but undiagnosed patient. However, this has not been proven.
“Although Nipah is a very serious infection, it is unlikely to pose a significant risk of global spread as the risk of person-to-person transmission is low, The R0 is less than 1.0. Nevertheless, we cannot be complacent as we have seen recently, some virus can mutate to increased infectivity. Also the long incubation period makes detection at borders very difficult.”
Declared interests
Prof Piero Olliaro: “I have nothing to declare – no funding whether direct or indirect.”
Dr Kaja Abbas: “Principal investigator: LSHTM has received grant funding from Gates Foundation for the research project “Health and economic impact of integrated nutritional activities to increase vaccination coverage in Chad and Niger”.
“Principal investigator:LSHTM has received grant funding from Gavi, the Vaccine Alliance through the Vaccine Impact Modelling Consortium for the research project “Vaccine impact modelling of HPV and measles”.
“Co-investigator:LSHTM has received grant funding from Save the Children for the research project “Barriers and solutions to reaching zero-dose and under vaccinated children in Ethiopia and Nigeria and to conduct an evaluation of Save the Children’s innovation incubator programmes in these respective countries”. Save the Children has received funding from GSK for their innovation incubator programmes in Ethiopia and Nigeria, which includes funding for the academic partner (LSHTM) for their research contribution.
“Collaborator: Nagasaki University has received grant funding from Japan Agency for Medical Research and Development for the research project, “SCARDA – Strategic Center of Biomedical Advanced Vaccine Research and Development for Preparedness and Response”.
“Supported by the International Vaccine Institute for serving as faculty in “GTH-B – Global Training Hub for Biomanufacturing”.
“Member of the UK JCVI (Joint Committee on Vaccination and Immunisation).”
Prof Ian Jones: “I declare no conflicts”
Dr Efstathios Giotis: “no conflict of interests”
For all other experts, no reply to our request for DOIs was received.