General Principles
Vaccine against smallpox contains a live virus, vaccinia, which produces cross immunity against variola major and minor.
Targeted vaccination and monitoring of contacts, together with isolation of cases, is the mainstay of containment. The efficacy of vaccination in preventing spread of the disease depends on early detection of cases and identification and tracing of contacts. This strategy of
ring vaccination is compatible with WHO recommendations.
Smallpox vaccination carries a risk of complications, which occurred at a higher frequency than that now acceptable for a modern vaccine. These complications occurred more frequently in people who were immunosuppressed, people with eczema and pregnant women. Because of this, mass vaccination of the population is not a first line option either prior to or in the event of an outbreak.
There is a need to consider protection of close contacts of people who have been vaccinated in view of shedding of vaccinia virus (eg. children with eczema should not share a house with someone who has been vaccinated until their vaccination site has completely healed).
Efficacy and take rate
Successful vaccination produces a
characteristic papule after 3 days. This evolves into a vesicle at 4 to 5 days and a pustule at 6 to 7 days. The pustule is a reliable indication that protective antibody levels have developed - ie. there has been a successful "take". A more rapid response is seen in persons who have had previous vaccination.
Take rates depend, amongst other things, on potency of vaccine, age of vaccinee, past vaccination history and vaccination technique.
For primary vaccination, take rates have historically varied from 85% to 99.9%. The primary take rate of an appropriately potent (10
8 pock-forming unit/ml) and properly administered vaccine is likely to be greater than 99%.
For revaccination, take rates have been lower, from 54% to 93% with a mean of about 70%. With the cessation of routine vaccination so long ago now, residual immunity is likely to be negligible, and any vaccination now is likely to resemble the primary vaccinations of the past.
For pre-exposure vaccination, a successful "take" provides full protection against smallpox. Post-exposure vaccination given up to 3 days after exposure also provides protection, although it may not completely prevent infection, and patients may develop mild modified disease.
Contraindications and complications
Contraindications to vaccination include eczema, immunosuppression and pregnancy, among others. Full details can be found in
Appendix 9.
Serious adverse effects associated with vaccination include inadvertent inoculation at other sites, generalized vaccinia, eczema vaccinatum
, progressive vaccinia and post-vaccination encephalitis. Full details can be found in
Appendix 10.
Surveys from the US have found that the overall risk of serious adverse events was between 50 and 1000 per million vaccinees, with inadvertent inoculation and generalised vaccinia the most common complications (
http://www.bt.cdc.gov/agent/smallpox/vaccine-safety/adverse-events-chart.asp).
However, this data may not be directly applicable to the current situation in Scotland and the rest of the UK:
Additional RSDRTs and SDEs.
Front-line clinical staff including designated ambulance workers.
Medical, nursing and support staff (porters, cooks, cleaners, laundry etc) who might be required to work at Smallpox Care Centres.
All laboratory staff who might be required to receive diagnostic clinical specimens (for EM and/or PCR).
Epidemiological staff who might be involved in contact tracing.
Mortuary staff who might be required to handle infected bodies.
Environmental health officers who may be required to decontaminate premises.
Individuals who might be required to join SSOCC or RSOCCs or the UK-NSOCC.
Additional vaccinators.
RSDRGs should identify these personnel within their Region at Alert Level 0. If possible, individuals should have received smallpox vaccine in the past, as they will have a faster immune response and a lower incidence of side effects.
Vaccination strategy at Alert Levels 2 and 3
In the event of confirmed smallpox in the UK, healthcare, emergency, laboratory and other essential personnel will be vaccinated as at Alert Level 1. The household contacts of these personnel will also be vaccinated.
In addition, other key workers (such as police and fire service personnel) may be vaccinated. These will be defined as required by the SEHD, and then identified by RSOCCs who will be responsible for arranging vaccination.
Smallpox Vaccination Centres will be activated on confirmation of the first confirmed case for vaccination of contacts of cases. Vaccination will be provided by nurses trained as vaccinators.
Clinicians should resist offering vaccination to individuals who demand vaccination without an epidemiological indication - ie. they do not fall into the groups of category A and B contacts.
Vaccination may be considered for travellers from Scotland or elsewhere in the UK to infected countries, or from Scotland or elsewhere in the UK in the event of an outbreak to countries that remain smallpox free. However this may be a major undertaking given the volume of travellers, and would be a low priority for use of vaccination resources.
Vaccination strategy at Alert Level 4
Circumstances may arise when mass vaccination may be required to raise the level of immunity to smallpox:
It is planned that sufficient stocks will be available to vaccinate the entire population of Scotland and the rest of the UK should this be necessary. Mass vaccination in Scotland and the rest of the UK will only be implemented at the direction of the SEHD in close collaboration with DH.
Vaccination strategy at Alert Level 5
Following an outbreak, at Alert Level 5, identified healthcare, emergency, laboratory and other essential personnel should be revaccinated annually, and in addition if they are re-exposed if this is more than 6 months since their last vaccination. Provided there are no contra-indications, the household contacts of these individuals should be encouraged to accept revaccination every three years.
Vaccination of essential personnel
Vaccination of essential personnel will be carried out by NHS occupational health nurses who have been trained as vaccinators and have themselves been immunised.
Essential personnel will be screened to ensure that neither they nor their household contacts has any contraindications to smallpox vaccine.
A central register of vaccinees will be maintained, and they may be asked to participate in research programmes to evaluate the vaccine.
An immune response will be verified before essential personnel are allowed to become involved in smallpox diagnosis, patient care, analysis of specimens or public health action.
Essential personnel will be revaccinated every 3 years at Alert Level 0 in order to guarantee immunity.