By Helen Petousis Harris 13/07/2018 4

In the tiny Pacific Nation of Samoa, on Friday 6 July 2018, two babies died shortly after receiving MMR vaccine. How could this happen?

Lots of discussion is going around about this tragedy, and even more questions. Here are some responses to the things I have been asked this week summarised under the headings below.

  • About MMR vaccines
  • How safe are MMR vaccines?
  • The risks of measles mumps and rubella
  • People who should forego the MMR vaccine
  • How can vaccination with MMR go wrong?
  • What happened in Samoa?

About MMR vaccines

MMR vaccines were originally developed in the 1970s to protect against measles, mumps, and rubella, in one convenient jab. However, there is a long history of the development and use of measles-containing these vaccines that extends back to the 1960s.

The measles-containing vaccines are called live vaccines. This is because the viruses in the formulation are viable, they can replicate. The viruses need to replicate to get the body to make an immune response that will be protective against disease but they have also been weakened so they are unable to cause disease. These vacciens are extremely effective with measles and rubella vaccines likely providing life-long protection.

It is hard to estimate exactly how many people in the world have received these vaccines but in 2016 85% of one year olds had received a dose of measles-containing vaccine, like the MMR. Given each year the world welcomes over 130 million newcomers the number of people having received these vaccines will be well in the billions.

An estimated 20.4 million lives had been saved between 2000 and 2016 through use of measles vaccine and way more during the preceding decades, however, even in 2016 over 89,000 deaths from measles occurred.

The point is, an awful lot of vaccine has been used and many lives saved!

How safe are MMR vaccines?

Short answer: Very.

Longer answer: Relatively common events associated with MMR vaccine are  Fever and/or mild rash 6–12 days after immunisation due to the measles component, fever and/or mild swelling under the jaw 10—14 days after immunisation due to the mumps component, fever, mild rash and/or swollen glands 2—4 weeks after immunisation due to the rubella component. Temporary joint pain 2—4 weeks after immunisation is more common in adult women than children.

Rare adverse events associated with MMR vaccine: Temporary low platelet count about 1/30,000; convulsion associated with a fever about 1-2 per million doses, Encephalitis less than 1 per million, infection free meningitis about 1 per 800,000 to 1 per million, and anaphylaxis 1 per million.

Yes there are some rare but serious risks.

How do we know? Nearly sixty years of safety surveillance and studies, the nature of which I have summarised in these pages previously.

Risks from those diseases

Here are some figures on the risks from measles, mumps, and rubella.

Measles: Ear infection (otitis media), diarrhoea, pneumonia, low platelet count, encephalitis (brain inflammation) for around 1 person out of 1000—2000 cases, weakened immune system, hospitalisation for around 1-2 person out of 10 cases death for around 1 person out of 1000 cases despite treatment, degenerative brain disease for around 1 person out of 100,000 cases, occurs years later and is always fatal. Measles during pregnancy increases the risk of miscarriage or premature birth.

Mumps: Fever, headache, swelling and pain of one or more glands under the jaw, viral meningitis for up to 15 people out of 100 cases, temporary deafness for around 4 people out of 10 cases and permanent deafness for around 1 person out of 15,000 cases, inflammation of the testicles or ovaries in adolescents and adults, nerve, joint, kidney, heart inflammation, encephalitis (brain inflammation) for around 1 person out of 6000 cases, which may result in death for 1 person out of 100, death for 1—2 people out of 100,000 cases, mumps during early pregnancy increases the risk of miscarriage.

Rubella: Some cases have no symptoms, which increases the risk of exposing pregnant women to the disease, rash and painful swollen glands, joint pain in adolescents and adults, low platelet count, encephalitis (brain inflammation) for around 1 person out of 6,000 cases. Rubella during early pregnancy can cause severe abnormalities in unborn babies including deafness, blindness, heart defects, and brain damage.

People who should forego the MMR vaccine

Because the MMR vaccine has live (albeit weak) viruses in it should not be given to some people. These people should not get the MMR vaccine:

  • Anyone who has experienced a severe allergic reaction (anaphylaxis) to a previous dose of any measles, mumps or rubella containing vaccine or any of the vaccine components.
  • Anyone who is acutely unwell. The presence of a minor infection is not a reason to delay immunisation.
  • Anyone with a diagnosed weakness of their immune system.
  • Anyone who has received another live injected vaccine, including varicella (chickenpox) or BCG vaccines, within the previous month.
  • Women who are currently pregnant (women should delay pregnancy for one month after having the vaccine). However there is no evidence of harm if this happens

How can vaccination with MMR go wrong?

Having mentioned the known risks with MMR vaccine above there are other things that can go wrong.

  • MMR vaccine often comes as a lyophilised powder (freeze dried). It needs to be reconstituted with a diluent, in this case sterile water for injection. There have been tragic occasions where instead of the vaccine diluent provided with the product another substance was inadvertently used to reconstitute the vaccine. If this substance is something like morphine, adrenaline, of anaesthetic the consequences are likely to be disastrous. An example of this occurred in Syria where it appears likely the vaccine was mixed with a muscle relaxant from the same fridge. Fifteen children died and a number of others were very ill.
  • Contamination of the vaccine by bacteria can happen when multi dose vials are used. While in NZ we use single dose vials, some countries use vials that contain five or ten doses. Once reconstituted these need to be used within a few hours then discarded. If left lying around in a warm place the growth of bacteria can set in. MMR vaccine has no preservative to stop this from happening. Using a damaged product can result in overwhelming sepsis and/or poisoning from toxins that the bacteria produce. A terrible case in the Sudan involved untrained workers and a single syringe for the whole 4-day campaign, and no access to cold chain. Like the Syrian disaster, fifteen children died, hundreds were ill.

However, even when the vaccine has been stored and handled properly things can still go wrong.

  • Vaccination with an underlying deficiency of the immune system. Sometimes people with immune deficiency, such as being on immune suppressive drugs like steroids, chemotherapy, or having an inherited immune deficiency, or HIV infection, or undiagnosed blood cancer, may be inadvertently vaccinated with a live vaccine. What happens? Usually nothing. However, there is a risk that their immune system isn’t working well enough to control the replicating vaccine virus. This could develop a disseminated vaccine-related infection.
  • Investigations might find that the person had an undiagnosed underlying condition, something that sat dormant waiting for the right trigger. There are many infectious diseases that do this, such as influenza, herpes viruses, hepatitis viruses, chicken pox… Very occasionally a vaccine can do this too.

Finally, despite best practice there are some events that are unavoidable. Very, very, rarely a previously healthy person will have a serious allergic reaction to MMR vaccine which can be treated.

What happened in Samoa?

Until the investigations have been completed and reported on we cannot say what did happen.

However, given the batch of vaccine involved had been in use in that country since August last year, and given the same batch of vaccine has been used in South American countries and the Caribbean island nations without incident, it seems unlikely that there was anything wrong with the vaccine.

The reports from the parents of the children affected on Friday indicate the reactions occurred within minutes after vaccination. This would preclude a response to the vaccine viruses as this takes at least a week. While anaphylaxis occurs within minutes and can be fatal when not treated the odds of seeing this twice in a day at the same place, given a chance of 1 in a million doses, is literally astronomical.

Global experts are assisting Samoan authorities in their investigation. We still need to understand what happened then implement measures to prevent such a thing from happening again. On top of the tragic loss of two children there is also the loss of trust in the health professionals that seek to protect people.

4 Responses to “How safe is the MMR vaccine?”

  • Many thanks for this.
    I assume this must be due to some mistake (ie human error) in preparation of the vaccine for injection as you suggest.
    Some years ago there were deaths in Syria when instead of water an anaesthetic agaent was used to reconstitute the MMR vaccine. I am sure something similar will have happened here.

  • Thank you, Doctor. Your excellent efforts at comprehensible vaccine explanation are really appreciated, far and wide. I hope you find it rewarding; you deserve to.