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Measles and the importance of maintaining vaccination levels

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Measles is caused by the paramyxovirus which spreads through airborne droplets. The disease has an incubation period of between six and 19 days. People with measles are usually infectious for one to two days before the rash appears but the total period during which an individual is infectious is not known.

Abstract

VOL: 100, ISSUE: 26, PAGE NO: 52

Helen Bedford, PhD, RGN, RHV, FRCPCH, MFPH, is lecturer in child health, Centre for Epidemiology and Biostatistics, Institute of Child Health, London

Measles is caused by the paramyxovirus which spreads through airborne droplets. The disease has an incubation period of between six and 19 days. People with measles are usually infectious for one to two days before the rash appears but the total period during which an individual is infectious is not known.

In the prodromal period (early stages of the disease), which lasts two to three days, the affected person may have signs and symptoms including;

- Fever with an associated pryexia;

- Cough and cold;

- Conjunctivitis;

- Feeling generally unwell.

In the day or two before the rash develops, some people develop Koplik’s spots. These appear on the buccal mucosa on the inside of the cheek and look like grains of salt on a red background (Fig 1).

The rash appears on the fourth day of the illness and is red and blotchy. It starts at the hairline and travels down the body over a period of about three days. The rash occurs mainly on the face and upper body (Fig 2). After three to four days it becomes a brownish colour and gradually fades. The fever usually subsides before the rash disappears.

Measles has an immunosuppressive effect, which may leave people at greater risk of infections for a period of months after an attack (Strebel et al, 2004). Immunity after natural infection is believed to be lifelong and exposure to further measles infection may boost this immunity (Strebel et al, 2004; Davies et al, 2001; Richardson et al, 2001).

Complications

Measles remains a significant cause of death among children globally. There are about 40 million cases of measles each year and 800,000 deaths worldwide, with half these deaths occurring in Africa alone (De Quadros, 2004).

Most of the evidence concerning the complications of measles has been gathered from the period before the introduction of measles vaccines when large epidemics occurred. Latterly, data has been available from outbreaks among unvaccinated people in Europe and the US.

One of the largest sources of information is a study of the complications of measles among 55,589 cases in England and Wales in 1963. The overall complication rate was 6.7 per cent, and risks were higher in children less than one year old and in adults.

Complications included:

- Encephalitis affecting one in 1,000 cases;

- Respiratory complications affecting 38 per 1,000 cases;

- Twelve deaths (Miller, 1964);

- Convulsions (febrile and non-febrile) at a rate of about one in 200 (Miller, 1978).

Rarer complications include subacute sclerosing panencephalitis and idiopathic thrombocytic purpura.

Subacute sclerosing panencephalitis (SSPE)

SSPE occurs some years after a measles infection. It is a progressive degenerative disorder of the central nervous system caused by reactivation of a defective form of the measles virus that lies dormant in brain tissue. The effects of this condition are similar to new variant Creutzfeld-Jacob disease (Miller, 2002).

The risk of developing SSPE following measles is about four per 100,000 cases. It is 18 times more likely in children who had measles under the age of one year compared with those over the age of five years (Farrington, 1991). It is also about three times more likely in boys.

Idiopathic thrombocytic purpura (ITP) 

ITP is a disorder in which the patient has a low platelet count that results in problems with clotting. The exact incidence of ITP is not known although it is thought to affect about one in 5,000 cases (Strebel et al, 2004).

Malnourished and immunocompromised patients

Measles can have serious consequences for people who are either malnourished or have a compromised immune system. Reports from four UK cancer centres between 1974 and 1984 identified that measles was associated with 15 out of 51 deaths in children in their first remission from leukaemia (Gray et al, 1987).

More recently, a London hospital reported that two children aged eight and 13 years who had renal transplants at the age of two years experienced measles-associated encephalitis. Both children had received one dose of MMR before their transplants but neither had been able to have a second dose (Kidd et al, 2003). It was reported in the news that both these children had been left with brain damage and physical impairments (The Sunday Times, 4 April, 2004). 

Management

Little can be done to alter the course of a measles infection once it is established, and treatment is essentially symptomatic. 

After contact with an infected person the disease may be prevented by the administration of a vaccine that contains measles. This must be given within three days.

Human normal immunoglobulin (antibodies) may also prevent infection following contact with the disease. It should be given within six days, but may have some benefit if given later.

Sources of information on measles

Information about measles in England and Wales is gathered routinely from a number of sources:

- Statutory notifications of clinically diagnosed cases to the Office of National Statistics (ONS);

- Reports of laboratory-confirmed cases from the Health Protection Agency (HPA); 

- Since 1994, follow-up of notified cases with testing of oral fluid for measles immunoglobulin M (IgM) (antibodies). 

It has been a statutory requirement for nearly 100 years for doctors to notify a proper officer of the local authority of cases of certain infectious diseases. The proper officer is usually the consultant in communicable disease control (CCDC). This notification ensures that there is a local investigation and action to control the disease.

Measles became a notifiable disease in 1940. The CCDC is required to report the numbers of cases of disease each week to the registrar general at the ONS. This whole process allows local as well as national disease surveillance to occur.

Data is published in various forms (McCormick,1993). One of the main limitations of notification data is that some diseases are under-reported and it has been estimated that only 40 to 60 per cent of cases of measles were notified in the past (Clarkson and Fine, 1985). Notifications still provide very useful information on disease patterns over time.

Confirming measles

When a measles case is notified, a sample of oral fluid should be tested for measles IgM to confirm the disease. The sample should be collected within six weeks of the onset of the infection. It is returned to the specialist Enteric, Respiratory and Neurological Virus Laboratory (ERNVL) at the HPA. 

All confirmed measles infections (whether by saliva testing or other method) are reported by laboratories in England and Wales to the Communicable Disease Surveillance Centre of the HPA (Ramsay et al, 2003).

Incidence of measles

Before the introduction of a vaccine, epidemics of measles occurred every two to three years. Fig 3 shows measles notifications from 1950 to 2002. In an average epidemic year there were more than 500,000 notified cases in England and Wales, with a peak of 763,531 notifications and 152 deaths in 1961.

Measles is highly infectious and in communities where immunisation is not available almost all children acquire the infection before the age of 15 years.

Impact of vaccination

The introduction and widespread use of measles vaccine has had a significant impact on the incidence of measles. The measles vaccine was first introduced in the UK in 1968 when it was recommended for children aged between one and two years. Throughout the 1970s and 1980s, uptake of the vaccine remained below 80 per cent (Ramsay et al, 2003). Even at this level the number of measles cases declined (Box 1).

Following the introduction of the combined measles, mumps and rubella (MMR) vaccine in 1988, uptake improved and reached over 90 per cent for the first time in the UK.

Notifications declined to very low levels but in 1994 a measles epidemic was predicted. One explanation for this was that a large proportion of school-aged children who were eligible for the measles vaccination before the MMR was introduced had never been vaccinated (Ramsay et al,1994).

Efficacy of the MMR

A single dose of a vaccine against measles is about 90-95 per cent effective. Statistics from other countries have shown that if a single dose of vaccine is used, there will be a period that is relatively free of disease, and then epidemics occur.

The spread of the disease results from gradual accumulation of susceptible individuals in the population. This susceptible group is made up of a combination of those who have never been vaccinated and those who have had only one dose of vaccine but who have not developed adequate immunity (Miller, 2002).

In the US, a second dose of vaccine was introduced in 1989 to combat this problem. To avert a large epidemic in the UK in 1994-1995, a mass immunisation campaign with a measles rubella vaccine (MR) was organised. The campaign was targeted at children aged 5-16 years. The campaign proved very successful and no measles epidemic occurred (Gay et al, 1997).

Following the campaign, a second dose of MMR was added to the routine immunisation schedule. This is given before children start school. The aim of the MMR vaccination programme is to eliminate measles (and mumps and rubella) and two doses of vaccine are needed to achieve this.

In countries such as the US and Finland where a two-dose programme of MMR has been in place for some years and high uptake has been achieved, very low levels of the three infections occur. In Finland all three diseases were eliminated in 1996 (Peltola et al, 2000).

A decreasing number of measles cases have been notified in England and Wales each year since 1995, with 2,500 in 2003. However, as measles have become less common, the accuracy of diagnosis has also decreased and in 1998-2001 fewer than 100 cases per year were actually confirmed as measles (Health Protection Agency, 2004).

Herd immunity

Because measles is so infectious, a high level of immunity is needed before herd immunity can be attained. Herd immunity occurs when a certain percentage of a population is vaccinated and the spread of the disease is effectively stopped. To reach this level of protection, about 85 per cent of preschool children should be immune (for this to happen 90-95 per cent need to be immunised with at least one dose of vaccine). The figures for immunisation of primary and secondary school children are 90 per cent and 95 per cent respectively. The current rates in the UK, and particularly in London, are well below this, with some areas only achieving between 60 and 70 per cent.

Recent outbreaks of measles

Since 1999 there have been outbreaks of measles in Europe, including Italy (2002), The Netherlands (1999-2000), the Republic of Ireland (2000) and England. These have all been associated with low vaccine coverage that:

- Never reached optimum levels (Italy and the Republic of Ireland);

- Was related to a specific population group (The Netherlands);

- Has declined because of adverse publicity over the safety of MMR vaccine (England).

These outbreaks serve as a potent reminder both of the need for sustained high vaccine coverage and how serious an outbreak of measles can be, even in industrialised countries (Box 1).

Outbreaks of measles in the UK

Since 2000, measles outbreaks in England have been reported. These have been the result of the low uptake of the measles vaccine in some communities (Morgan et al, 2003; Hanratty et al, 2000). Uptake overall has fallen from 92 per cent in 1995 to 80 per cent in 2003, with lower uptake in some areas, notably London. Mathematical modelling has shown that if the current low level of MMR coverage persists in the UK, measles will re-establish itself as a frequently occurring (endemic) disease (Jansen et al, 2003). 

The decline in the uptake of the vaccine is the result of publicity surrounding a paper that suggested an association between the MMR vaccine and the development of autism and bowel problems in children (Wakefield, 1998). Research has since been conducted to explore this link and there is convincing evidence that the MMR vaccine does not cause autism (DeStefano and Thompson, 2004; McCormick et al, 2004).

Public health initiatives

NHS Immunisation Information, part of the Department of Health’s communicable disease team, is responsible for promoting and providing information about the childhood immunisation programme.

This includes: placing advertisements in a variety of media including TV; leaflets translated into different languages; and factsheets. 

Additional resources have been developed specifically focusing on the vaccine in response to the negative publicity over the triple vaccine. An MMR website has been set up that provides the public with clear factual information and a facility for asking questions (www.mmrthefacts.nhs.uk).

NHS Immunisation Information also provides central support for the training of health professions. This national service has been augmented by local developments.

Since 1991, HPE has conducted regular surveys of parental knowledge and attitudes to immunisation. This information shows that most mothers seek advice from health professionals when deciding whether or not to have their children immunised (Ramsay et al, 2002).

Local initiatives

In Wales an initiative has been developed to assist health professionals in advising parents. It is recognised that parents place value on the advice of health professionals. It is also acknowledged that it can be difficult in a busy clinic to get all the relevant facts and present them to parents in a professional manner.

It was felt that existing resources are not easy to use in this situation and a tool was developed to facilitate discussion. The MMR mythbuster pack examines the 10 most common myths in an easy to digest form. The pack was distributed to all practices in Wales early in 2001 (Roberts, 2001)

In 2002, the 20 health authorities with the lowest uptake of MMR vaccine were asked by the Department of Health to produce an action plan for increasing vaccine uptake locally. Central funding was provided to cover the costs of the proposed initiatives. These included training health professionals, providing them with local information on vaccine uptake and disease prevalence, providing events for parents, and working with local media.

Conclusion

Measles is a potentially serious illness, even in industrialised countries. It is important that high levels of vaccination are achieved and sustained. Health professionals, in particular nurses, have an important role to play in this and it is essential that they keep up to date with the evidence. This will enable them to advise parents effectively when they request information about MMR vaccine and to offer reassurance to allay fears over the most recent scare story.

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