The elimination of measles by 2010 is part of the strategic plan for measles and congenital rubella infection in the European Region of the World Health Organization (WHO Euro). Many European Union (EU) countries are on the right track to reach this goal, but some problems still need to be solved; according to the data reported to EUVAC.NET, there are still several thousand measles cases reported in the EU annually . Public health experts are well aware that the hardest efforts towards elimination of a disease usually have to be performed in the end phase of elimination programmes, when new and often unexpected issues arise and need to be faced in a short time.
A two-dose schedule of the combined measles, mumps and rubella vaccine (MMR1 + MMR2) is nowadays included in all EU immunisation programmes. In nine Member States, catch-up campaigns are also carried out . However, several European countries only recently implemented the second dose of MMR and the vaccination coverage in a number of EU countries is well below the >95% needed for achieving herd immunity.
To avoid interference with maternal antibodies passively transmitted to the infant it is common knowledge that the MMR1 should not be administered too early in life. On the other hand there is a window of susceptibility to measles infection between the decay of passively acquired maternal antibodies and the start of the immune response elicited by vaccination. The right timing for administration of the MMR1 is determined by balancing the need to minimise the length of this window period to the development of an optimal immune response to the vaccine.
So far, providing the first MMR dose to children aged >=12 months has been the golden standard. In EU countries, MMR1 is offered between 12 -18 months of age. In certain situations, as in France an early start is recommended for children attending day-care (MMR1 at 9 months of age followed by MMR2 at 12-15 months) or as in most countries before travelling to countries with wild-type measles circulating (MMR1 provided from 9 months of age). The MMR2 is usually offered after the 3rd year of life, with the exception of Austria and Germany where the MMR2 recently was recommended before the age of two.
In this issue, Cilla and colleagues compare the levels of measles-specific antibodies in two groups of parturient women in Spain who gave birth in 1990 (end of the epidemic period) and in 2006 (after eight years without virus circulation), respectively. The results from this survey are in line with similar studies recently carried out in Europe [2-4]: in the post-vaccination era the antibody levels in young adults are lower than those in the same age groups when the wild-type measles virus was widely circulating.
The issue of waning immunity after measles vaccination has been largely debated [5-8], especially in relation to the possibility of increasing number of measles cases in young adults. According to observations in settings where measles has almost been eliminated, such as in Scandinavia and the Americas, high vaccination coverage and active outbreak control may limit the effect of imported measles cases.
In the present situation, with wild virus still circulating in Europe and observed waning immunity, a discussion on a possible policy change with the first MMR dose provided at an earlier age may be warranted . Scientific evidence could support such a change, including the research reported by Cilla and colleagues.
However, several issues have to be taken into account in the EU actual scenario. Anticipating the MMR1 before 12 months of age can definitively lead to the risk of development of a lower immune response to the vaccine in many children (especially those who received sufficient passive immunity from their mother). In such a situation the introduction of a policy change could add more interferences than real benefits. Changing the MMR vaccination schedule should be a public health decision taken after a thorough analysis not only of the available scientific evidence but also of many practicalities. At present, a general agreement on offering the MMR1 at 12 months of age in all EU countries would be a good compromise.
In addition, other health care measurements, besides those already implemented, may prove useful. Many of the recently measles infected individuals in Europe including in those countries close to elimination were in the age groups 25-50 years, too old to be offered measles vaccination, too young to be infected by natural measles and catch-up campaigns were never performed. To reach elimination for a disease like measles in our modern mobile societies close to all susceptible individuals need to be immunised. To obtain this goal and reach all the age groups that are susceptible, several alternative strategies could be tried such as; continue high vaccination coverage of all children with the two-dose schedule, offer measles vaccination to all age groups without a history of natural disease, offer all age groups who received one dose of measles a second dose to avoid breakthrough infections, offer measles vaccine to travellers to countries with endemic measles; offer measles vaccine to women planning to become pregnant with no history of natural measles or vaccination and include measles in the antenatal screening of pregnant women with no history of measles infection and vaccinate after delivery against measles.
Moreover, we actually do not know very well which level of protection is obtained long-term following the two doses of MMR vaccine, including the role of cellular immunity . Many children are born to mothers in their third or fourth decade of life, and the long-term immunological memory after the varying vaccination schedules now in use within the EU ought to be evaluated. A third dose of MMR later in life may prove to be necessary in the future, especially in those countries with a well implemented measles immunization program and with steadily high coverage levels.
At present, however, the priority should be to strengthen existing measles elimination programmes and assure high vaccination coverage for two doses of MMR: it is important to keep in mind that most of the problems linked to waning immunity could be solved once the elimination goal has been reached.