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Scientists comment on news that the first case of Clade Ib Mpox has been detected in the UK.
Prof Michael Marks, Professor of Medicine at the London School of Hygiene & Tropical Medicine (LSHTM); and Honorary Consultant in Infectious Diseases at the Hospital for Tropical Diseases, University College London Hospital, said:
“The mpox virus itself isn’t that transmissible as it relies predominantly on direct skin-to-skin contact with a person who is currently unwell with mpox. By contrast, the COVID-19 virus transmits through the air and a lot of transmission occurs from individuals who have mild symptoms or are asymptomatic, which is why it can spread so widely. By comparison the mpox virus is much less transmissible.
“Wherever there are a large number of cases occurring in a part of the world people are traveling to and from, there is always some risk of a small number of mpox cases being introduced into other countries. We need to make a distinction between the risk of one or two cases being imported into other parts of the world, as we’re currently seeing, versus this leading to onwards transmission and widespread outbreaks in that country.
“Sweden has not had further cases arising from its imported case and in the UK, the risk that there will be lots of other cases arising from this imported case is again low. So, although there is, and I anticipate will continue to be, a large number of cases occurring in Africa, the likelihood overall that there will be an epidemic on the scale of the COVID-19 pandemic is extremely low.
“Although the clade I mpox viruses appear to cause slightly more serious illness, overall, outcomes for most people are good and patients typically have a mild or self-limiting illness from which they will fully recover. The healthcare system in the UK is ready to respond to mpox cases and has excellent access to infectious diseases teams, specialist care and vaccines.
“The priority must continue to be on supporting the countries most affected with the release of adequate funding or vaccination to control this mpox outbreak. The teams in DRC are very experienced, and with the right resources, they can handle it. But what’s required is vaccine access.”
Prof Azra Ghani, Director, MRC Centre for Global Infectious Disease Analysis, and Dr Lilith Whittles, Lecturer, MRC Centre for Global Infectious Disease Analysis, both Imperial College London, said:
“Clade 1b mpox is a newly emerged strain of the mpox virus that has been circulating in central Africa for several months. At present, sustained transmission via human-to-human contact is only occurring in this region, with international efforts underway to end this outbreak through prompt case isolation, contact tracing and vaccination of close contacts and high-risk populations such as health workers. Epidemiological characterisation of the virus is ongoing. While infections with the ancestral clade 1 have been more severe than seen in the 2022-23 global outbreak of clade IIb, severity of the current clade 1b remains unclear. Severity likely depends on age, underlying co-morbidities such as immunocompromising conditions, and availability of supportive healthcare.
“Vaccination against clade 1b has only just begun, so clade-specific vaccine effectiveness has not yet been precisely measured, however given the high protective efficacy of vaccination observed against clade IIb during the global 2022-23 outbreak, it is highly likely that current vaccines will offer strong protection.
“Given continued circulation of the virus, it is not unexpected that isolated cases will arise in non-endemic regions, as indicated by recent cases in Sweden and India. Given that infection only occurs through close physical contact, the risk of onward transmission is low. However, the case acts as a timely reminder that it is essential that support continues to be provided to end the ongoing epidemics in the central African region.”
Dr Jonas Albarnaz, Institute Fellow, The Pirbright Institute, said:
“An outbreak of clade 1 mpox virus is ongoing in DRC since 2023, with thousands of cases suggesting sustained human-to-human transmission there. The emergence of the new clade 1b variant changed this picture as it spread to other African countries (e.g., Burundi, Kenya, Rwanda), driven mostly by sexual networks involving young adults. Since then, sustained community transmission of this variant has been seen in Burundi as well. However, there is no evidence that clade 1b virus transmits better or cause a more severe disease than clade 1a. Clade 1 mpox virus is known for causing more severe disease in young children, pregnant women, and immunocompromised people.
“Since the emergence of clade 1b mpox, countries implemented surveillance and contact-tracing strategies to detect possible importations early on following WHO recommendations. These measures enabled the detection of imported clade 1b cases in Sweden, Thailand, India, and Germany in individuals with recent travel history to affected countries in Africa. However, further transmission to close contacts has not been reported in neither of these countries outside Africa.
“Sporadic cases outside Africa are expected to happen whilst the outbreak in Africa is not brought under control. Vaccination remains the best strategy to prevent mpox and is recommended to individuals at higher risk of infection, which include contacts of mpox cases, healthcare workers, and people with multiple sexual partners. Two vaccines are approved against mpox: MVA-BN and LC16. These vaccines are based on weakened versions of a related orthopoxvirus (vaccinia) and were developed against smallpox (now eradicated). However, availability of these vaccines is very limited, representing a major bottleneck for the control strategies.”
Prof Paul Hunter, Professor in Medicine, UEA, said:
Is this surprising or expected?
“This is not at all surprising, we were bound to see clade 1b infections arriving in the UK at some point. It is actually surprising to me that it has taken so long after the first reports of clade 1b spreading in Africa.
Are there other European countries which have had imported cases from returning travellers and what has happened there?
“As far as I am aware there have been reports from Sweden and from Germany. However, I am not aware of the outcomes of these cases. So far at least there do not appear to have been any secondary cases in contacts of these, although it is early days from the German case which was only reported about a week ago. But just because none have been reported from other countries does not necessarily mean that there have been none. Mpox clade 2b is still circulating throughout Europe and it is very difficult to distinguish the two. Not all such infections will be diagnosed, particularly in people who were previously vaccinated due to being at risk of clade 2b. Even when diagnosed it is very difficult to distinguish the two clades other than by gene sequencing which may not always be done in all European countries.
What do we know about clade 1b mpox and how it is transmitted?
“Clade 1b mpox arose in the Democratic Republic of Congo (DRC) just over a year ago. Both clades 1a and 1b are focussed in the DRC. Clade 1a predominantly affects children and it is believed that many of these infections are acquired from contact with infected animals. Clade 1b is mostly spreading between adults through intimate and sexual contact. Recently, however, clade 1b does seem to be affecting children more at least within the DRC.
Is this a concern for the general public?
“Probably not. Mpox is not that infectious unless with very close contact. Early reports were that clade 1 infections are more severe than clade 2 infections and this caused particular concern. However, it is not clear how much of that difference in severity was driven by the poorer health care facilities in DRC compared to West Africa or by the intrinsic virulence of the virus.
“It is likely that if mpox clade 1b does spread in Europe, it would spread predominantly in the same sexual networks that clade 2b spreads in. It is unlikely that we will see a similar epidemic with clade 1b as we saw with clade 2b. The reason for this is that vaccine given for 2b is also effective against 1b and people who have had an infection with 2b will also have reasonable protection against 1b, though not 100%.
What are the measured being used to try to minimise the chance of transmission?
“The primary control measure is vaccination, though encouraging people, especially those at risk of more serious disease, to reduce the number of different sexual partners they have is also important. Where a case is identified their sexual and household contacts would be traced and offered advice and vaccination if appropriate. Vaccination still has value even if only given after exposure.
Any other comments about this development?
“No but here is the latest sitrep report, the section for clade 1b on page 6 is worth reading: https://www.who.int/publications/m/item/multi-country-outbreak-of-mpox–external-situation-report–41–26-october-2024.”
Dr Brian Ferguson, Associate Professor of Immunology, University of Cambridge, said:
“The UK Health Security Agency (UKHSA) announced today that it has detected a single confirmed human case of Clade Ib mpox in the UK. This case is from an individual who has recently returned from travelling in countries in Africa where there are currently cases of Clade 1b mpox being found in the community. This is an unsurprising event and likely will not be the only time this happens in the UK. It follows discovery of similar imported cases in Germany and Sweden and other countries globally. The close contacts of this individual are being sought and should be offered testing and vaccines in line with current policy to help reduce the chances of onward transmission. The UK government recently purchased 150,000 doses of mpox vaccine from Bavarian Nordic to help with such efforts, although the longevity of the protection afforded by this vaccine has recently been called into question. The clade 1b mpox is more virulent than clade 2 virus that caused the outbreak in 2022 and is causing more cases of disease in younger people than the clade 2 virus in Africa. As such continued surveillance and early diagnosis and treatment is very important to minimise the chances of onward transmission of imported cases.”
Prof Jonathan Ball, Deputy Vice-Chancellor, and Professor of Molecular Virology, Liverpool School of Tropical Medicine, said:
“This is not unexpected. There are active human to human transmission chains of Clade 1b monkeypox infections in several countries in sub-Saharan Africa, and therefore people coming into close contact with anyone infected is at risk.
“WHO previously announced the Mpox outbreak a public health emergency of international concern in recognition of its potential for continued and potentially accelerated spread if the global community did not come together in a concerted effort to stamp out the current outbreak. This was more recently backed up by the announcement yesterday of activation of the Global Health Emergency Corps to strengthen the response.
“The number of cases reported outside of Africa remains low, but the ability of Clade 1b virus to spread by human to human transmission means that this issue can not be ignored. It is unlikely that we will see extensive outbreaks in countries with well developed public health and surveillance systems, but it is a reminder that we need to do more to remove health inequalities around the world.”
https://www.gov.uk/government/news/ukhsa-detects-first-case-of-clade-ib-mpox
Declared interests
Prof Michael Marks: “No conflicts.”
Prof Azra Ghani:
“- Institutional research funding from: Medical Research Council, Community Jameel, NIHR, the Wellcome Trust, NIH, Bill and Melinda Gates Foundation, WHO, The Global Fund, Gavi, Coalition for Epidemic Preparedness (CEPI), Integrated Vector Control Consortium (IVCC), Medicines for Malaria Venture, Asian Development Bank, PATH;
– Student project funding from AstraZeneca related to COVID work;
– Personal consultancy: GSK, Sanofi, HSBC, Pacific Life Re related to COVID webinar participation; AstraZeneca related to RSV, The Global Fund related to malaria;
– Non-renumerated advisory: IMF (COVID), Moderna (COVID vaccines), CEPI (scientific advisory board), Gavi (Vaccine Investment Strategy), WHO (Malaria policy);
– Trustee for Science Media Centre;
– Former trustee and special advisor, Malaria No More UK;
– Visiting Professor, Lee Kong Chian School of Medicine, Nanyang Technical University, Singapore.”
Dr Lilith Whittles:
“- Institutional research funding from: Medical Research Council, Community Jameel, NIHR, the Wellcome Trust, NIH;
– Personal consultancy: Pacific Life Re related to COVID webinar participation; WHO-EURO modelling report on mpox clade IIb in Europe;
– Non-renumerated advisory: WHO R&D Expert Working Group on modelling for epidemic and pandemic threats; Wellcome Research Steering Group for “Seroepidemiology in Africa for iNTS vaccines (SAiNTS)”;
– I hold an honorary mathematical modeller position at UKHSA, advising on Group A Strep and mpox.”
Dr Jonas Albarnaz: “No conflict of interest to declare.”
Prof Paul Hunter: “None.”
Dr Brian Ferguson: “I don’t have any conflicts of interest.”
Prof Jonathan Ball: “None.”
For all other experts, no reply to our request for DOIs was received.