Could a measles epidemic return to New Zealand?

Low measles vaccination rate concerns experts

Measles is a highly contagious disease which can only be prevented by immunisation. Low immunisation rates and travel between areas/countries where measles is circulating can allow the disease to spread. Most recently, outbreaks of measles have been occurring in New Zealand in 2011, particularly in the Auckland region.

As at 22 November 2011, the Auckland Regional Public Health Service (ARPHS) advised there were 346 confirmed or probable measles cases in the Auckland region (since 30 May 2011). Of these, 63 cases have required hospital treatment.

Two doses MMR vaccine in childhood
The measles vaccine is given as part of the combined measles-mumps-rubella (MMR) vaccine. On the childhood Immunisation Schedule, one dose of MMR is given at age 15 months and one dose of MMR at four years. The two doses are required to provide more effective protection against measles.

Auckland immunisation rates low
The ARPHS says (July 2011) that immunisation rates in Auckland region are low, with only 78% of children aged 18 months having received one dose of MMR vaccine, and for 18-month-old Maori children in Auckland region only 67% have received one dose.

Measles epidemics in New Zealand 
Statistics given by the New Zealand Ministry of Health, in its ‘Immunisation Handbook 2011’, state that large scale outbreaks (epidemics) of measles occurred in New Zealand in 1997, 1991, and 1984/85. In the 1997 epidemic, 2169 cases of measles were notified.

Hospital admissions due to measles numbered 400 in 1984/85, and 943 during the 1991 and 1997 epidemics. During the 1991 epidemic, seven cases died from measles, four of whom were unimmunised children.

More recently, in 2009, 248 cases of measles were notified, with most of these attributed to three outbreaks, the largest of which was in the Canterbury Health District (170 cases).

UK statistics
In the UK, measles made a comeback in 2008, with 1000 cases reported; among them two deaths. This is nearly 13 times the number reported for the UK in 2007.

Should we be worried about a resurgence of the disease in New Zealand? Yes we should, according to Dr Nikki Turner, Director of the Immunisation Advisory Centre (IMAC).

The upsurge of cases in the UK has been linked to a decline in vaccination levels there. Here, too, vaccination rates are well below the optimum level needed and Dr Turner (interviewed in 2009) makes the same connection: “Because measles is so infectious, it will spread very easily if the immunisation rates are low enough.”

What is measles?
In most people, measles causes moderate symptoms but, in a few, it can lead to serious complications and even death. For more information see our health topic on measles.

Vaccination against measles was first introduced in New Zealand in 1969, and it has evolved over time, bringing a greatly reduced rate of infection and death. With the current low vaccination levels, however, this may not always be true.

How vaccination works

Immunisation programmes for infectious diseases like measles only prevent epidemics if there are enough immunised people in the population to prevent the spread of the illness; a state known as herd immunity. “Measles is so infectious,” explains Dr Turner, “that if someone in a room sneezes it’s like an aerosol spray; everyone gets exposed. If you are not vaccinated [or have not already had the disease], you will get measles.”

For measles, herd immunity is said to be reached when at least 90% - and preferably 95% - of the population is immunised. Current estimates put the New Zealand MMR (measles-mumps-rubella) immunisation rate at around 80% [can be lower in some regions], well below that needed to give herd immunity.

Dramatic fall in measles following vaccine introduction

Up until the late 1950s, the number of people who died of measles reached 20-40 people every three to four years. This number dropped in the 1960s to around 15-20 deaths every three or four years, and the introduction of a vaccine in 1969 saw a further decline in deaths but not an end to measles epidemics, with the most recent epidemic in 1997.

It was during this 1997 epidemic that the Ministry of Health implemented an intensified campaign to immunise children against the disease. Despite the fact the vaccination programme began when the epidemic was already established, it is estimated the number of new cases was reduced by 90-95% as a result. Perhaps most important was the fact no one died during this epidemic, compared with seven deaths in the 1991 epidemic.

Changes to the timing of vaccination

Back in 1990, the measles vaccine was replaced by the combined measles-mumps-rubella (MMR) vaccine. It was recommended the first vaccination take place at 15 months, with a repeat at 11 years.

In 2001, the Ministry of Health changed the recommended schedule for the MMR vaccination after research suggested a new regimen would prevent the epidemics that were continuing to occur every five to seven years.

The MMR vaccine is now scheduled for 15 months and four years.

Reason for vaccination decline

In 1998, a single, small case-based study of 12 children proposed a possible link between MMR and autism. Several very large-scale studies using hundreds of thousands of people have since refuted that link but, despite this, ongoing discussion in the media has had a major impact on vaccination rates in several countries.

Thiomersal: a bit of a red herring

Just to complicate matters, a separate issue has become mixed-up with the MMR vaccine; that of the use of thiomersal (also known as thimerosal) as a preservative in some vaccines. Thiomersal contains mercury. It used to be used in some childhood vaccines and some people have suggested a link between this and autism. However, thiomersal has never been used in the MMR vaccine. In fact, no childhood vaccine in New Zealand contains thiomersal.

Public health and immunisation experts are very concerned about a possible return to the measles epidemics of the past. Governments around the world continue to assure the public that the MMR vaccine is safe and effective in minimising the threat of measles, as well as mumps and rubella (or German measles).

Further information

For more information on childhood vaccination visit the Immunisation Advisory Centre. To get your child vaccinated, contact your Plunket nurse or your GP. Discuss any concerns about vaccination or possible side effects with your nurse or doctor before vaccination.

Related topics

Also see: Childhood immunisation and Measles and Vaccination - how it works

Original material provided by everybody. Reviewed by Dr Helen Petoussis-Harris of the Immunisation Advisory Centre (IMAC), April 2009. Photos of children with measles courtesy of Centers for Disease Control and Prevention. Updated by everybody, July and November, 2011.