Public Health Note: Monkeypox

This disease appears to be less infectious than Covid-19. It is less readily spread by airborne transmission., and there is less asymptomatic transmission of monkeypox than of Covid-19. The mode of transmission of monkeypox means it is unlikely to cause the rates of infection seen during the Covid-19 pandemic. 

The period for which a person with monkeypox is currently considered to be infectious is from the first day they show symptoms of the disease until the day their last scab falls off. This can be a period of several weeks.

We do not yet have a good estimate of the R number for monkeypox. Because transmission relies on close contact, the individual behaviours of infected people have more of an impact on how the disease spreads than the baseline infectiousness of the virus. ‘Close contact’ can take these forms:

• Contact with contaminated material, such as handling bedding, clothes or towels used by an infected person. At this stage, we do not believe this extends to any surface touched by an infected person being a risk for others.
• Face to face contact with an infected person via large droplet transmission, while neither party is wearing PPE, including coughs, sneezes, and conversation.
• Direct physical contact with an infected person including hugging, kissing, sexual intercourse.
• Household contact sharing a house with an infected person will generally expose you to all three of the risks above.

Currently, a higher proportion of cases are being reported among men who have sex with men than in other demographic groups. This does not mean that only men who have sex with men are at risk from infection.

Infected animals can transmit monkeypox to humans. Touching an infected animal (living or dead), or eating improperly cooked meat from an infected animal can lead to infection. Animals which can contract monkeypox include squirrels, rats, and primates native to Central and West Africa. It is possible that other animal species, including those native to the UK, can become infected as well. A previous outbreak in the USA was linked to infection spreading to pet prairie dogs.

Monkeypox causes skin lesions similar in appearance to chickenpox. The modes of transmission described above are primarily due to contact with the contents of these lesions. Droplet transmission is possible because these lesions can develop in the mouth, meaning saliva expelled while talking, coughing, or sneezing contains infectious material from those lesions.

The relative proportions of cases which are caused by large droplets as opposed to contact with contaminated surfaces, skin on skin contact, or sexual transmission is not yet known.

People who have a lot of close contact with multiple people, particularly sexual partners, are most likely to be exposed to monkeypox virus in a manner which causes infection.

• In most cases, the virus initially causes flu-like symptoms including headache, fever, chills, sore throat, feeling generally unwell, fatigue, and swollen lymph nodes. Within 1-5 days of the flu-like symptoms appearing, a rash develops which often begins on the face and then spreads across the body. The rash occurs in all cases of the disease. These lesions eventually scab and fall off. The lesions and scabs readily transmit virus to other people. A person is considered infectious from the day of their first symptom until their last scab has fallen off.
• The incubation period for monkeypox (time between infection and onset of symptoms) varies between 5 and 21 days.
• The infection is mild for most people, and symptoms last for 2-3 weeks. However, pregnant women, people who are immunocompromised, and children have a higher risk of developing complications or severe disease than the general population.
• Monkeypox diagnosis must be confirmed by a healthcare professional. PCR testing is available to clinicians making diagnoses, but not to the general public in the way Covid-19 testing has been available.
• Monkeypox lesions can vary in number and size from person to person. They can look similar to chickenpox lesions. In regions where monkeypox is endemic, it is sometimes mistaken for chickenpox. Generally, monkeypox is more likely to come with swollen lymph nodes, fever before the lesions develop, and slower development of lesions than chickenpox. The lesions themselves are generally painful in monkeypox (until they begin to scab), whereas chickenpox lesions are itchy. These are typical differences between the diseases, but not 100% reliable, hence the need for a healthcare professional to confirm.
• Lesions caused by monkeypox infection can lead to permanent scaring.
• People who were vaccinated for smallpox in their childhood may have a milder disease, or be protected from infection. Smallpox vaccination was compulsory until 1971 and then discontinued when that disease was eradicated. Despite the visual similarities, chickenpox and monkeypox are from different virus families, and chickenpox vaccination provides no protection against monkeypox. 
• The number of recorded cases which lead to death, or Case Fatality Ratio (CFR) for this strain of monkeypox may be between 1 and 6%. A previous study in Nigeria estimated the CFR for the West African Strain, which is causing the current outbreaks, as 3.6%. For other strains it has been reported as being as high as 10% for untreated cases. However, some of this data comes from records which had a low rate of follow-up for recorded cases (which is likely to lead to the CFR being overestimated). These rates include instances where the treatments available for the disease in the UK were not provided. As such, we do not yet have a reliable estimate of the CFR for this monkeypox outbreak in the UK.

Monkeypox is generally a mild illness from which people recover without medical treatment.

• Some antiviral treatments appear to reduce the symptoms and severity of monkeypox, and other viruses in the same family. They will not be required for the majority of cases.
• A vaccine for monkeypox and smallpox was authorised in 2019 (called Imvanex in the EU, Jynneos in USA, Imvamune in Canada).
• Being vaccinated after you have become infected with monkeypox is believed to reduce the severity of your infection. The NHS is offering a vaccine to people who have been in close contact with people infected with monkeypox to reduce their risk of developing the disease.  

Although the relative importance of different modes of transmission is different between monkeypox and Covid-19, non-pharmaceutical interventions (NPI) that prevent Covid-19 infection are expected to prevent monkeypox infection. Namely:

• Avoid skin to skin or face to face contact with anyone who has symptoms of monkeypox.
• Seek medical attention if you develop a rash and have close contact with individuals you don’t know, or change sexual partners regularly.
• Practise safe sex.
• Wash your hands with soap and water or alcohol-based sanitizer frequently, and particularly after skin on skin contact with a symptomatic person or a stranger.
• Catch coughs and sneezes in a tissue, elbow or hand, and then dispose of or sanitize the receptacle.
• Stay at home if you feel unwell with flu like symptoms or a rash.
• Infected people should isolate themselves while they are symptomatic. Ideally, infected people should inform any close contacts they have had since the onset of their symptoms. This is so that those people can monitor themselves and isolate if they develop symptoms.
• People who have had a ‘high risk’ close contact (see below) with someone who was symptomatic should isolate for 21 days.

People who have symptoms of monkeypox should be encouraged to report them to the NHS, and supported in the event that they need to isolate.

• When a person has been diagnosed with monkeypox by a healthcare professional, it would be wise for their workplace to inform anyone who has worked closely with them while they were infectious that they may have been exposed. Those people should monitor themselves for symptoms, or if they have been in high risk contact, they may need to isolate (See the UKHSA guidance note below for precautions which should be taken following different types of exposure). Workers who should isolate according to the UKHSA note should be supported in doing so by their employer.
• Follow the recommendations for reducing transmission.
• Stay abreast of new developments and guidance.
• Prepare contingency plans for workplace outbreaks. An outbreak may result in staff who work closely together needing to avoid coming to work for several weeks. Some may be able to work remotely for some of this period, and others may be too ill.

Follow advice from the UKHSA and government, available here and here. At the time of writing these state:

• Anyone with an unusual rash or lesions on any part of their body should contact NHS 111 or a sexual health service.
• If you frequently come into close contact with people you don’t know, or if you change sexual partners regularly and you develop a rash, seek medical advice.
• Contact with an infected person is defined as: within the period between a person’s first symptom, and ending when all their scabs have fallen off, face to face exposure, direct physical contact, or contact with contaminated materials.
• People who have been in contact with an infected person in the manner defined above should be monitored daily for symptoms of infection for a period of 21 days from last contact. Contacts should monitor their temperature twice daily for a fever of 38°C (100.4°F) or more.
• You must isolate for 21 days (including not going to work) if you have been in a ‘high risk’ close contact situation with a person who has been diagnosed with monkeypox and was symptomatic at that time. Note that ‘high risk’ describes the nature of the contact and not a situation where either person is clinically vulnerable. The UKHSA defines high risk close contact as:

“Direct exposure of broken skin or mucous membranes to monkeypox case (once symptomatic), their body fluids or potentially infectious material (including on clothing or bedding) without wearing appropriate PPE1

This includes:

• inhalation of droplets or dust from cleaning contaminated rooms
• mucosal exposure to splashes
• penetrating sharps injury from contaminated device or through contaminated gloves
• people who normally share a residence (either on a permanent or part time basis) with a person who has been diagnosed with monkeypox, and who have spent at least 1 night in the residence during the period when the case is infectious” 

WHO Monkeypox Factsheet WHO, 19/05/22

Monkeypox: background information UKHSA Guidance, Gov,uk, 24/05/22

Conditions: Monkeypox NHS, 24/05/22  

Monkeypox contact tracing classification and vaccination matrix, UKHSA, 20/05/22

European Public Assessment Report: Tecovirimat European Medicines Agency, 28/01/22

IMVAMUNE® and ACAM2000® Provide Different Protection against Disease When Administered

Postexposure in an Intranasal Monkeypox Challenge Prairie Dog Model, Keckler et. al. Vaccines 2020

WHO News: Multi-country monkeypox outbreak in non-endemic countries WHO, 21/05/22

Vaccinating against monkeypox in the Democratic Republic of the Congo, Petersen et. al., Antiviral Research, 2019

The changing epidemiology of human monkeypox—A potential threat? A systematic review Bunge et al., PLOS, 11/02/22

Human monkeypox: confusion with chickenpox, Jezek et. al., Acta Tropica, 1988

Article: A CDC expert answers questions on monkeypox Stat News, 19/05/22

Article: WHO expects more cases of monkeypox to emerge globally, Reuters, 21/05/22 

Article: UK to announce more monkeypox cases as efforts ramp up to contain outbreak Guardian, 22/05/22 

Monkeypox: What do we know about the outbreaks in Europe and North America? BMJ News, 20/05/22