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Mpox (monkeypox) is a rare disease that is caused by infection with mpox virus, a DNA virus. With the eradication of smallpox in 1980 and subsequent cessation of smallpox vaccination, it has emerged as the most important orthopoxvirus. Mpox occurs sporadically in central and western parts of Africa’s tropical rainforest.
There are two distinct viral clades; one found in the Congo basin of central Africa, and the other in west Africa.
As mpox is related to the virus causing smallpox, vaccines designed for smallpox will provide a level of protection. Previous data from Africa suggests that previous vaccines against smallpox may be up to 85% effective in preventing mpox infection.
Mpox is included in the national list of High Consequence Infectious Diseases (HCID) in England and is a notifiable disease.
Human-to-human transmission occurs through close physical contact by two main routes:
It can also be transmitted from mother to child, and from contact with an infected animal or through eating the meat of an infected animal.
Typically, mpox has an incubation period of between 5 and 21 days.
The Smallpox vaccine available is a Modified Vaccinia Ankara – Bavarian Nordic (MVA-BN). It is currently distributed under two brand names, although it is the same vaccine.
The brand names are
The vaccine can be administered by the deep sub-cutaneous or intramuscular route (see Immunisation procedures: Green Book chapter 4). The preferred site is the deltoid region of the upper arm.
In August 2022, following the emergency use approval by the US Food and Drug Administration, the Joint Committee on Vaccination and Immunisation (JCVI) endorsed the use of a fractional dose (0.1ml) of MVA-BN given by intradermal injection during periods of supply constraints. The approach has also been advised by the European Medicines Agency Emergency Task Force. EMA’s Emergency Task Force advises on intradermal use of Imvanex / Jynneos against monkeypox | European Medicines Agency (europa.eu). A fractional dose intradermal injection for MVA-BN may be administered on the deltoid (the same site recommended for BCG - see Green Book chapters 29, 32 and 4) or on the volar aspect (palm side) of the forearm around 2-4 inches below the ante-cubital fossa (the same site as normally used for Mantoux testing).
The virus used in the vaccine is an attenuated strain that cannot replicate in mammalian cells. It should be considered an inactivated vaccine.
While MVA-BN (Imvanex®) efficacy studies were aimed at understanding its protective efficacy against smallpox, many of the licensing studies have used challenge with mpox virus.
The vaccine has recently been authorised for active immunisation against mpox in adults in the UK by the Medicines and Healthcare Products Regulatory Agency (MHRA) (https://products.mhra.gov.uk/search/?search=IMVANEX)
In 2022 Welsh Government confirmed that areas with localised outbreaks were to be prioritised in the distribution of UK-wide supplies of the mpox vaccine. As more stock of vaccine became available health boards were able to recommence offering pre-exposure vaccination.
Currently health boards invite individuals who have received a first dose for a second dose, at the frequency prescribed by the clinical advice. The intradermal dose sparing technique continues to be used for both first and second doses, given the pan-Wales pilot undertaken did not raise any clinical concerns.
Any individuals who have not received their primary dose will still have access to vaccination through the ‘Nobody left behind’ principle. It is recommended that everyone who is eligible for the vaccine to take up their offer as soon as possible.
The initial priority was to deliver first doses to as many in the highest risks group as possible. In September 2022, due to the number of vaccines already given, the reducing incidence and the current vaccine supply the JCVI agreed that the next priority is to offer a second dose to GBMSM at highest risk from around 2-3 months after their first dose. Offering second doses to the existing high-risk eligible group completes their primary course, thus maximising their direct protection and indirect protection via their contribution to current and future transmission. This approach would likely result in some vaccine doses remaining available for use in outbreaks.
JCVI proposed that vaccination should be offered as soon as feasible to gay, bisexual and other men who have sex with men (GBMSM) at highest risk due to a large number of contacts.
The committee agreed that GBMSM at highest risk could be identified amongst those who attend sexual health services, using markers of high-risk behaviour similar to those used to assess eligibility for HIV pre-exposure prophylaxis (PrEP), but applied regardless of HIV status. These risk criteria would include a recent history of multiple partners, participating in group sex, attending sex on premises venues or a proxy marker such as recent bacterial sexually transmitted infection (in the past year).
In view of the current epidemiology and vaccine supply available, wider vaccination in low risk GBMSM individuals or the general population is not advised at this time.
Individuals who are identified through contact tracing of confirmed cases will continue to be prioritised and offered post-exposure vaccination where this is indicated.
There is very limited evidence on the effectiveness of post-exposure vaccination using MVA-BN, and therefore vaccine should be prioritised and individuals be risk assessed for those most likely to benefit. This would be based on timeliness of vaccination following exposure and for individuals at higher risk of severe disease following infection.
It is recommended that post-exposure vaccination of high-risk community or occupational contacts is offered ideally within 4 days of exposure, although may be offered up to 14 days in those at ongoing risk, or those who are at higher risk of the complications of mpox.
The JCVI has also recommended that during periods of supply constraint, post exposure vaccination offers should be prioritised. Post exposure vaccination for contacts will be prioritised for those at greater risk of severe disease, including children under the age of five, pregnant women and people who are severely immunosuppressed. In addition, people eligible for pre-exposure vaccination, for example high risk gay and bisexual men, may be offered post-exposure vaccination. See Pre-Exposure Vaccination section above.
Like all medicines, the vaccine can cause side effects, but not everybody gets them. The common side effects are:
The most common side effects reported are at the site of injection. Most are mild to moderate in nature and cleared without any treatment within 7 days. Intradermal (ID) injection was associated with a higher rate of itchiness and local reactions such as erythema and induration when compared to subcutaneous injection, although pain at the injection site was less common than after subcutaneous administration.
Other reactions are rare. For more information on common and rare side effects, see:
(These are external pages and are not monitored by Public Health Wales.)
Vaccination programme recommendations from the Joint Committee on Vaccination and Immunisation (JCVI) and Welsh Government policy can be found at the links below.
Joint Committee on Vaccination and Immunisation - GOV.UK (read JCVI publications and statements; search e.g. Mpox)
Intradermal injection technique training video:
Administration of the MVA-BN Vaccine Using an Intradermal Injection Technique | Turas | Learn (nhs.scot) This short video resource produced by NHS Education for Scotland (NES) demonstrates the correct administration of MVA-BN vaccines using an intradermal injection technique. [NES Version 1 December 2022].
Wales Monkeypox Training Addendum 31 October 2022 - These slides are an addendum to current training packages and should be used only in conjunction with “Vaccination against monkeypox using the MVA-BN vaccine: training for healthcare practitioners” 20 October 2022, published by the UKHSA
UKHSA Monkeypox vaccination training slide set 20 October 2022.
Clinical resources and information
Smallpox vaccination against Monkeypox checklist v1 Bilingual
What you need to know Intradermal monkeypox vaccination Billingual
Patient Specific Direction (PSD) Template for mpox vaccination available on the Welsh Medicines Information Centre (WMIC) available at: Monkeypox - Welsh Medicines Information Centre (wales.nhs.uk)