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An outbreak of measles in Canterbury has prompted huge demand for vaccinations, but what is the disease and how serious is it really?
This Q&A explainer lays out the facts ...
What is measles?
Measles is one of the most infectious contagious disease known, infecting children as well as adults via coughing, sneezing or talking. It is not known to affect any other species.
People who come into contact with the disease who are not immune through vaccination or previous infection are about 90 percent likely to become infected.
Before vaccines, 90 percent of people over 20 had been infected at some point in their lives.
About one in 10 people who contract measles need hospital treatment. The virus can live in the air for hours after a person has been coughing and sneezing in the area.
Symptoms - of fever, cough, runny nose and watery 'pink' eyes, and sometimes small white spots on the back inner cheek - start 7-18 days after exposure.
Another 3-7 days later, usually about 14 days after exposure, a blotchy rash which can last up to a week tends to start on the face and head before spreading down the body.
Symptoms can last for about two weeks total.
People with the disease become infectious about five days before and after the rash appears.
Spread by contact with respiratory secretions through coughing and sneezing.
Infected persons should stay in isolation - staying home from school or work
The best protection from measles is to have two MMR vaccinations. MMR is available from your family practice and is free to eligible persons
People are considered immune if they have received two doses of MMR vaccine, have had a measles illness previously, or were born before 1969
Anyone believing they have been exposed to measles or exhibiting symptoms, should not go to the ED or after hours' clinic or general practitioner. Instead, call the GP first.
Measles can also lead to complications.
Up to 30 percent of people infected can develop complications including ear infections with the potential to cause deafness (7%), diarrhoea (6%), pneumonia (6%), seizures and - in one in 1000 cases - swelling of the brain which leads to permanent brain damage about a third of the time.
There is also a longer term risk of subacute sclerosing panencephalitis, a rare fatal disease developing seven to 10 years after contracting measles despite seeming to fully recover.
SSPE is thought to occur in about four to 11 of every 100,000 people who contract measles. The risk may be higher for those who contract it when they are younger than two.
How deadly is measles?
Measles can kill.
The highly contagious nature of the disease means individuals' overall risk of death from an outbreak is higher than for other diseases simply because they are more likely to contract it.
CDC reports death in 0.1 to 0.2 percent (one or two in every thousand people infected) between 1985 and 1992 in the US.
New Zealand last had a large epidemic in 1991, with about 7000 cases and 7 deaths.
However, measles has a 50 percent death rate for New Zealand children with low immunity, the Ministry of Health says.
The World Health Organisation reports that before the introduction of measles vaccine in 1963, major epidemics occurred every two or three years, causing an estimated 2.6 million deaths a year.
Pneumonia accounts for 60 percent of measles deaths, while swelling of the brain from measles is 15 percent fatal.
The likelihood of death in people with malnutrition is also comparatively high, about 10 percent, particularly for those with a vitamin A deficiency.
Adults and children aged under five are also more at risk than older children.
Is measles still common?
Measles still occurs throughout the world but particularly in Africa and Asia where vaccination rates are lower.
It is the world's most common vaccine-preventable cause of death among children.
In New Zealand, two separate outbreaks caused 595 people to contract the disease in 2011, mostly in Auckland.
Outbreaks have been reported in the Philippines, parts of Europe and New Zealand this year.
New Zealand is one of just seven countries to have officially wiped out home-grown cases of measles and rubella, according to the World Health Organisation. Since 2012 all cases have originated overseas.
In total this year, 40 people in New Zealand are recorded as having measles between 1 January and 10 March.
That combines 25 people affected by the outbreak in Canterbury, 10 affected in an earlier outbreak in Waikato, and scattered individual cases in other regions.
The World Health Organization has targets to eradicate measles worldwide.
An outbreak in Papua New Guinea last year killed 72 children.
What should I do if I think I have measles?
Because of the risk of contagion, people who have measles are being advised they should not visit their GP, emergency department or after hours clinic.
Instead they should remain isolated, call their GP or free Healthline on 0800 611 116 for advice and wait at home. They should not go to school, childhood centres, work, sports events, social activities, shopping malls or use public transport.
Doctors have said calls made to GPs after hours will be answered by a nurse who will advise what to do and where to go.
There is no specific treatment for measles, but pain relief, drinking plenty of water, avoiding bright light and treating sore eyes by wiping crusted eyelids and lashes using cotton wool and water can help relieve some of the symptoms.
GPs and other health professionals are advised not to wait for confirmation of measles, but to advise the Medical Officer of Health as soon as it is suspected.
If a person with measles has any of these symptoms, their doctor should be contacted:
a stiff neck
feels drowsy or cannot be woken
coughing up green or yellow thick mucous
having a fit (seizure)
not passing urine for 10 hours
People with measles should remain in isolation until 14 days after symptoms end.
Is the vaccine effective? How common is vaccination?
The MMR vaccine is cheap and hugely effective in preventing measles.
Two doses of the vaccine prevents the disease in 95 percent of people aged over one year old, and 98 percent of people aged over 18 months.
A single dose is still quite effective, providing 90 to 95 percent protection, but some people do not respond to it. A second dose is required to ensure success.
Doses must be at least a month apart.
In New Zealand between 1969 and 1990, it was standard practice for doctors to give just one vaccine. People born during this time should confirm that they have had two MMR vaccines.
The vaccine might not be effective in people who have only been vaccinated within the past two weeks, as they may be already infected. The vaccine is not a cure, but it can still provide protection if given within 72 hours of exposure.
The Health Ministry's director of public health, Dr Caroline McElnay, last year said 95 percent of eligible children and infants had received their first dose, and 90 percent the full vaccine.
About 110,000 people are estimated to have died worldwide from measles in 2017.
About 85 percent of children globally are vaccinated, the WHO estimates.
Global measles deaths have decreased by 80 percent from an estimated 545,000 in 2000 to 110,000 in 2017. The WHO estimates measles vaccination prevented 21.1 million deaths in that time.
However, cases in Europe in 2018 were their most numerous of the decade, with infections largely affecting clusters of unimmunised people.
In New Zealand, children should be vaccinated at 12 months and four years of age.
It is important for a majority of a population to be vaccinated to prevent outbreaks, which can afflict the unvaccinated, those with weakened immune systems and a very small minority (about 2 percent) of vaccinated people.
A rate of 95 percent immunity across the population is advised to prevent the disease from circulating, the WHO advises.
Who can get the vaccine?
In New Zealand, the MMR vaccine - which also prevents Mumps and Rubella (also known as German measles) - is free to anyone born after 1969.
People born before then are believed to be at lower risk because they were likley exposed as a child.
During an outbreak, additional vaccines can be given for those aged over six months.
Pregnant women should not get immunised. Women are advised to avoid pregnancy within 28 days of receiving the vaccine. Pregnant women who contract measles are at risk of miscarriage, premature labour, and low birthweight. It is fine to get the vaccine if you are breastfeeding.
Babies under 12 months usually do not receive the vaccine, but this limit is reduced to 6 months during an outbreak.
Those who have experienced a severe allergic reaction (anaphlaxis or hypersensitivity) to a previous dose of any measles vaccine or vaccine components should seek medical advice. Egg allergy does not affect the vaccine.
People who have had a blood transfusion within the past year should seek medical advice.
People who have compromised immune systems from treatments or disease should not receive the vaccine. In particular, chemotherapy erases the body's memory of the virus. People taking medication to suppress their immune system should seek medical advice.
Cancer patients who have finished chemotherapy can be reimmunised after six months, for free.
How do I check if I'm vaccinated?
People who are not sure whether they are vaccinated should check their Well Child Tamariki Ora or Plunket book, or contact their GP.
People who cannot find their records are recommended to get a (free) vaccine.
Getting more than the recommended two vaccines is not harmful.
The National Immunisation Register rolled out in 2015 only had MMR added recently, so people are unlikely to find their records there, especially those born before 2005.
New immunisations during the Canterbury outbreak are being added to the register.
What's the situation in Canterbury?
At least 25 people have contracted the disease in Canterbury in the latest outbreak which began about two weeks ago.
Vaccines have largely run out in the region, but are being resupplied today with an extra 18,000 doses expected in practices from Wednesday.
That followed 3000 extra vaccines being brought in the previous week.
GP teams have been asked to prioritise the following groups for MMR immunisation:
People who are not up-to-date according to the schedule for their age-group
Children and young adults (age range 5 years to 28 years) who are either not immunised or who have only received one MMR dose to date.
Children 12 months to 5 years who have never received any doses of MMR.
Adults aged 29 to 50 (this group only received one dose of measles vaccine).
In an outbreak, an additional dose of measles vaccine can be given to people aged over six months. Infants given a vaccine before the age of 12 months should still get two more scheduled doses.
Are there risks to getting the vaccine?
Getting the MMR vaccine is considerably safer than the risks from contracting measles.
Within 12 days, up to 15 percent of children who receive the vaccine experience a fever, and 5 percent experience a rash. This is mild and not as dangerous as measles.
This fever or rash is not measles, and people who have had the vaccine are not infectious.
About 1 in 800,000 doses can lead to a (recoverable) inflamed meninges. Acute brain inflammation occurs in about one in a million people, though this is unlikely to be caused by the vaccine.
An allergic reaction is even less likely. However people receiving vaccines, and the guardians of children receiving the vaccine, are asked to stay 15 minutes after it is administered in case anaphylaxis occurs.
This compares to a death rate of one in 1000 people infected by measles, which has a 90 percent chance of infected those who have not been immunised. The risks of measles are far greater, not to mention the risks of Mumps or Rubella.
A now debunked study suggested a link between MMR vaccines and autism. The author was found to have falsified his results and scientists have since been unable to find any support for such a link despite hundreds of studies.
Is this outbreak all the fault of anti-vaxxers?
Canterbury health officials have said vaccine mistrust is "only one piece of the puzzle" regarding the outbreak.
The former practice of only administering one vaccination and people aged under four who had not yet had their second dose were also being affected.
However, doctors have also warned that the rise of anti-immunisation sentiment has caused a reduction in children being vaccinated, with an estimated 5 percent drop in Northland.