MMR vaccine

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MMR is a mixture of three live viral vaccines. They protect against measles, mumps, and rubella.

People born in the UK prior to 1980 are likely to have natural immunity to these three diseases. All those born since should be offered two doses of MMR, separated by at least four weeks, with the first dose given after the age of 12 months, and the second dose after the age of 18 months.

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Early Immunisation

  • In the event of an outbreak or exposure to a case MMR may be given to infants from the age of 9 months, and a second dose may be given 4 weeks after the first.
  • Any doses given before the age of 12 months do not count as the "first dose"; and any doses given before the age of 18 months do not count as the second dose required for long-term protection.[1][2][3]
  • This is because maternal antibodies may destroy the vaccine viruses before the body has had a chance to mount a new immune response to it.
  • (This advice has since been amended to bring it in line with practice, and possibly with new evidence - the second dose in some parts of the UK is given three months after the first, and policy is now as described below.)

Immunocompromised people, non-immune pregnant women, and infants under the age of 9 months who are exposed to measles cases may also be offered immunoglobulin - see measles article for more detail.

There is a cohort of people who may only have been offered a single dose, but who may have received a measles and rubella vaccine (without mumps) - more details are available in the "Questions and answers about mumps and MMR" article.

Useful websites about MMR include:

MMR was introduced into the standard UK immunisation schedule in 1988.

Contents

Epidemiology

Measles fell sharply after immunisation was introduced

Measles fell sharply after immunisation was introduced and now affects no more than one percent of people under the age of 30 in countries with routine childhood vaccination.

The CDC report on the effect of vaccination against measles in African countries in 1996-2002 shows that vaccination markedly reduces the mortality rate due to measles.[4]

Rubella fell sharply when immunisation was introduced.

The MMR vaccine was introduced to induce immunity less painfully than three separate injections at the same time, sooner than at three separate encounters, and more efficiently than either.

By increasing the time until immunised, spacing the components inevitably increases opportunities for infection with at least two of the diseases for the individual and their contacts.

A survey of 1000 patients in the northwest UK by Durham University found 7% of parents had opted for single vaccines, but only 19 out of 72 children had received them all. The overall uptake of MMR there was 85%.[5]

Dose and schedule

The routine schedule in most parts of the UK is to give the first dose of MMR at the age of 12 or 13 months, and a second dose as part of the pre-school booster. In some parts of the UK, where the risk of measles is higher, the second dose is given three months after the first dose. (See the Green Book - pp216-7 of chapter 21 gives chapter and verse.)

Each individual should be offered two doses of MMR that meet the following criteria to count (“qualifying doses”):

  • The first qualifying dose must be given after the age (from birth, regardless of gestational age at birth) of 1 year;
  • The second qualifying dose must be given at least 3 months (90 days) after the first qualifying dose, if given before the age of 18 months; or at least 28 days (but preferably 3 months) after the first qualifying dose, if given after the age of 18 months. ((Previous guidance said that the second dose should be given three months after the first if aged <18 months; and could be given at least 4 weeks after the age of 18 months. This has now been revised to recommend a minimum interval of three months between doses in most cases.)
  • Additional doses of MMR (e.g. before the age of one year, or a second dose too soon to count as the second qualifying dose) will do no harm, and may even be recommended in the event, e.g., of an outbreak; but do they do not count towards the recommended total of two (“qualifying”) doses.

Rationale for additional doses of MMR vaccine

MMR is live virus vaccine. It contains live, attenuated viruses: versions viruses which cause of the measles, mumps, and rubella that have been modified so that they don't cause disease, but still stimulate the body to generate antibodies which will protect you against the disease-causing "wild" viruses.

When the viruses multiply or "replicate", the body's immune system is stimulated to respond. As well as producing antibodies, the immune system will remember the virus, and will be able, very rapidly, to produce further antibody if it encounters the virus again.

If you already have circulating antibodies against any of the diseases, the vaccine viruses won't multiply ("replicate"). This means they don't stimulate the immune system to produce more antibodies, or immune memory. Serious side effects from vaccination are almost entirely due to the viral replication. When vaccine is given to somebody who is already immune there will be no viral replication, so the risk of an adverse reaction is lower. Even in a naive (non-immune) person adverse reactions are uncommon - MMR has been extremely extensively studied, and is one of the safest medical interventions in existence.

During pregnancy antibodies in the mother's bloodstream can pass through the placenta and into the baby. This happens particularly in the last 8 weeks or so of pregancy. Babies (especially those born at term - less so in premature babies) are born with these transplacental antibodies, which provide it with "passive" immunity, protecting the baby against many of the diseases to which their mother had immunity. The babies have no immune memory of their own against these infections. The antibody levels in the baby's bloodstream depends on their mothers' antibody levels. The maternal antibodies gradually disappear from the baby's system.

If there are sufficient maternal antibodies against them, the vaccine viruses in MMR will not replicate and stimulate immunity in the baby. This is why we vaccinate after 12 months, not before; it's because earlier vaccination likely to be ineffective due to maternal antibodies.

Not all babies will have maternal antibodies against all three diseases. Although sufficient levels to prevent vaccination have been documented as late as 15 months of age, in most cases the levels will have dropped sufficiently for vaccination to be effective by the age of 12 months. The levels of antibody required to prevent infection are probably higher than the levels which will prevent the weaker vaccine viruses from replicating, so many babies will be vulnerable to infection before they are vaccinated. This is partly why herd immunity is so important: the baby is unlikely to be exposed to any of the diseases the vaccine prevents.

As a result of vaccination, and the herd immunity it produced, there are mothers who have not been not been vaccinated, or in whom the vaccine did not work, and who have not been exposed to measles, mumps, or rubella, and who will have no immunity at all: their babies will, of course, have no maternal antibodies.

Women who've been vaccinated typically have lower antibody levels than those who had natural infection, and so do their babies, so their immunity doesn't last as long; so an increasing number of babies will be vulnerable from an earlier age.

If a baby is likely to be exposed to disease, it can be vaccinated earlier than 12 months BUT this is an EXTRA dose. Doses given before 12 months may be ineffective, due to maternal antibodies, so an early dose does NOT count towards the 2 doses everybody should have.

Additional doses (before 12 months, or before minimum interval) will do no harm, but may not be effective.

Evidence is mounting that mumps vaccine does not induce immunity for as long as had been hoped. Immunity against mumps wanes over time - including, it would appear, immune memory; and it is thought that the resulting "secondary vaccine failure" may be partly responsible for outbreaks of mumps in young adults (although this is not the full story). There is a possibility that an fourth dose of MMR may be recommended for adolescents - partly as an opportunity to "catch up" individuals who have not had two doses already, and partly to boost immunity against mumps to prevent secondary vaccine failure.

As healthcare workers are at increased risk of exposure to the three viruses their immunity status is important in preventing hospital outbreaks. According there is an argument for determining their immunity status especially if they intend to practice in areas such as paediatrics, and given that they themselves rarely consider the significance of choices their parents may have made on their behalf many years before[6].

Mumps Component

The viral strain is called Jerryl Lynn. These are the names of the daughter of the principal researcher and from whom the precursor of the vaccine strain was isolated and cultured. Later when nucleic acid sequencing became available there turned out to be two minimally different sub-strains.

MMR scare

QuotationMarkLeft.png If I were to suggest that between the Earth and Mars there is a china teapot revolving about the sun in an elliptical orbit, nobody would be able to disprove my assertion provided I were careful to add that the teapot is too small to be revealed even by our most powerful telescopes. But if I were to go on to say that, since my assertion cannot be disproved, it is intolerable presumption on the part of human reason to doubt it, I should rightly be thought to be talking nonsense. If, however, the existence of such a teapot were affirmed in ancient books, taught as the sacred truth every Sunday, and instilled into the minds of children at school, hesitation to believe in its existence would become a mark of eccentricity and entitle the doubter to the attentions of the psychiatrist in an enlightened age or of the Inquisitor in an earlier time. QuotationMarkRight.pngBertrand Russell[7]

There was an unfounded scare about MMR in the late 90s. This had differential impact based on cultural factors such as use of the English language, worldwide. It took 12 years for the research article that started the scare to be retracted by the Lancet, partially because some relevant information only came out after formal investigation by a regulatory body despite other attempts at investigation[8]. The media continued to report this as a controversy, giving anti-vaccinationists a lot of air time and column-inches, incorrectly implying that the profession was split about this issue - whereas in fact the overwhelming majority of those that had studied the issues (and possibly all informed professionals who didn't have an ulterior motive) believed that MMR is very safe indeed. A significant proportion of parents made a conscious decision not to have their children vaccinated.[9]

Evidence from large, well-performed studies, shows that:[10][11][12]

  • People with autism and bowel disease are no more likely to have received MMR than controls.
  • People who are given MMR are no more likely to go on to develop autism or bowel disease than controls.
  • There is no association between changes in the incidence of autism or bowel disease and MMR uptake - indeed, in countries such as Japan, where MMR useage stopped because of problems with vaccine supply, autism rates have continued to rise.

Many people who believe that MMR (and other vaccines) are excessively dangerous, in the face of evidence to the contrary, have a near religious belief, as implied by Brian Deer,[13] citing Russell's teapot. [14]

Coverage

Coverage with MMR dropped from 90.8% in 1997-98 to a trough of 79.9% in 2003-4 and reached 91.2% in 2011-12. The WHO target is 95%. [15]

See also

References

  1. De Serres G, Boulianne N, Meyer F, Ward BJ. Measles vaccine efficacy during an outbreak in a highly vaccinated population: incremental increase in protection with age at vaccination up to 18 months. Epidemiol Infect 1995;115(2):315-23
  2. van den Hof S, Wallinga J, Widdowson MA, Conyn-van Spaendonck MA. Options for improvement of the Dutch measles vaccination schedule. Vaccine 2003;21(7-8):721-4
  3. Redd SC, King GE, Heath JL, Forghani B, Bellini WJ, Markowitz LE. Comparison of vaccination with measles-mumps-rubella vaccine at 9, 12, and 15 months of age. J Infect Dis 2004;189 Suppl 1:S116-22
  4. MMWR Weekly 2004 53(02);28-30 (January 23)
  5. R Casiday, T Cresswell, D Wilson, C Panter-Brick. A survey of UK parental attitudes to the MMR vaccine and trust in medical authority. Vaccine 2006;24:177-84
  6. Loulergue P, Guthmann JP, Fonteneau L, Armengaud JB, Levy-Brühl D, Launay O. Susceptibility of health care students to measles, Paris, France. Emerging infectious diseases. 2011 Sep; 17(9):1766-7.(Link to article – subscription may be required.)
  7. Russell B. Is There a God? (Article commissioned, but not published by Illustrated magazine in 1952.) Text of article available at [1] and at [2].
  8. [Retraction—Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children The Lancet, 2 February 2010 doi:10.1016/S0140-6736(10)60175-7]
  9. Pearce A, Law C, Elliman D, Cole TJ, Bedford H, the Millennium Cohort Study Child Health G. Factors associated with uptake of measles, mumps, and rubella vaccine (MMR) and use of single antigen vaccines in a contemporary UK cohort: prospective cohort study. Br Med J "Online First" 2008:bmj.39489.590671.25
  10. Social Market Foundation. Science, Risk and the Media: Do the front pages reflect reality?. 5th March 2006. ISBN Number: 1-904899-40-4
  11. Eric Fombonne, Rita Zakarian, Andrew Bennett, Linyan Meng, and Diane McLean-Heywood. Pervasive Developmental Disorders in Montreal, Quebec, Canada: Prevalence and Links With Immunizations. Pediatrics 118: e139-e150. (Full text available as pdf here
  12. Ray P et al. Encephalopathy after whole-cell pertussis or measles vaccination: lack of evidence for a causal association in a retrospective case-control study. Pediatr Infect Dis J 2006 Sep 25:768-73
  13. B Deer. Andrew Wakefield: surgeon paid to attack MMR shots faces medical council hearing. Last viewed January 12, 2007
  14. Russell B. Is There a God? (Article commissioned, but not published by Illustrated magazine in 1952.) Text of article available at [3] and at [4].
  15. FIgures from HSCIC reported in BMJ 1 Dec 2012

This article is a work in progress. Please feel free to contribute to it.

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