RELEVANCE OF COMBINED MEASLES-MUMPS-RUBELLA VACCINATION

Heikki Peltola, MD

HUCH, Hospital for Children and Adolescents

E-mail: heikki.peltola@hus.fi

Measles, mumps and rubella (MMR) are extremely contagious and potentially

dangerous infections of childhood for which mono-, bi- and trivalent live

virus vaccines are available. Measles is a recognized global killer (³1

million deaths a year), but what about mumps and rubella - should these

infections also be taken seriously?

The severity of mumps has been realized rather late. Meningitis and

orchitis are well-known entities, but there are many more. In general,

clinical mumps can be divided in those involving the central nervous system

(meningoencephalitis with or without EEG changes), the reproductive organs

(orchitis, mastitis, oophoritis), manifestations of the hearing organ

(transient or permanent hearing loss), and other manifestations such as

thyroiditis, pancreatitis and myocarditis. The incidence rates are difficult

to estimate because the diagnostic facilities are usually not there where

most of mumps currently occurs. From the military recruits - a special risk

group - in Finland (in the 1950s) derives the information that the incidence

mumps was as high as 3100 per 100,000. In the civil population, the rate was

lower. If an estimation for the mumps incidence of 2000 cases per 100,000

per year - derived from an old but prospective community-based study in the

USA (Am J Med Sci 1949;218:88) - is applied to the world's population, no

less than 120 million cases of mumps would occur annually. The true number

might be somewhat (but not much) lower since many countries have included

the mumps component in their immunization programs.

For nonpregnant woman and her fetus, rubella is a mild and benign

maculopapular rash disease which, becomes more prominent after hot bath.

Virus excretion from the nasopharynx may last for more than 2 weeks, but

viremia ends when rash abrupts. Curiously enough, rubella is not invariably

benign in non-pregnant individuals either; even deaths due to encephalitis

have been recorded. Those are, however, extremely rare. Somewhat more common

are various chronic and bizarre disorders due to rubella.

The problem is indeed in congenital rubella syndrome (CRS). If mother

contracts rubella in pregnancy, the risk of CRS might be up to 90% if

infection occurs during the first 10 weeks. Thereafter, the risk declines so

that it is almost nil after the 4th month. Global data are not available,

but when an epidemic swept over the USA in 1964-65, 20,000 cases of CRS

developed. All this tragedy is not yet over.

Since rubella poses a risk essentially to unborn children, it would be

logic to vaccinate only girls before they reach the childbearing age. This

selective vaccination was initially the accepted policy, until it was

realized that the incidence of CRS did not much decline; the male population

was responsible for continuous virus circulation in the community. Once

immunization was extended to males also, CRS became rare in countries which

launched extensively enough vaccinations. How sensitive this issue is, was

demonstrated in Greece a few years ago: Rubella immunization was started,

but because high enough vaccination coverage was not reached, an outbreak

developed. A few months later, the highest ever recorded incidence in Greece

of CRS followed.

In principle, it would be possible to immunize people against MMR diseases

one disease by one. It would, however, become very costly, risky, and slow

way to get rid of these serious infections. The recent experience from

Finland shows that countrywide elimination is well possible when a combined

MMR vaccine is used

- provided the following conditions are fulfilled: First, all vaccine

components must be immunogenic and safe. Second, at least two doses should

be administered because up to 5% of recipients do not respond to all three

components ("primary failures"), a two-dose regimen is likely to reach more

children, and waning immunity (slow decrease of antibody below protective

level, "secondary failures") seems a reality. Third, the vaccination

coverage - in a range of 95% - must be reached and maintained for years,

otherwise measles, mumps, or rubella will be brought back from abroad. This

has occurred in Finland also, but thanks to the high coverage, outbreaks

have not followed. We are, however, aware of that this possibility exists.

Therefore, serological cohort studies are running to disclose if alarmingly

low antibody levels will be observed. If so, an additional vaccine dose might

one day become necessary.