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Review confirms effectiveness of MMR vaccines; no association with increased autism risk

M3 India newsdesk May 22, 2020

Now it is official. A detailed, 423 page Cochrane review published on April 20, 2020 presents new evidence that confirms the effectiveness of MMR, MMRV and MMR+V vaccines and that those are not associated with increased risk of autism. 

Dr. Carlo Di Pietrantonj of Italy’s Regional Epidemiology Unit SeREMI led the review team. The present review is an update of a review published in 2005 and updated in 2012.

Cochrane Reviews are internationally recognised as the highest standard in evidence-based health care. Cochrane library publishes the reviews online and updates them regularly to incorporate new research, so that the stakeholders can base treatment decisions on the most up-to-date and reliable health evidence.

The MMR (measles, mumps, and rubella) is a combined vaccine that protects against all the three infections. Clinicians can vaccinate against varicella (chickenpox) by a combined MMR and varicella vaccine (MMRV) or can give it separately at the same time (MMR+V).

Measles, mumps, rubella, and varicella (chickenpox) can lead to serious complications, disability, and death. Sadly, public debate over the safety of the trivalent MMR vaccine started in 1998 when Andrew Wakefield and 11 other co-authors published a study titled “Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children ” in The Lancet.


Vaccine controversies

This paper triggered concern about a possible connection between the MMR vaccine and autism spectrum disorder (ASD). Other labs could not reproduce the results. In 2010, the General Medical Council ruled that Wakefield had acted “dishonestly and irresponsibly” in doing his research; the Council struck him off the Medical Register, meaning he could no longer practise as a physician in the UK. Shortly, The Lancet fully retracted the paper. Wakefield suffered more setbacks later.

The controversy led to many parents not allowing their children to be vaccinated. In spite of appropriate action though belatedly, anti vaccine movement got foot hold in many countries with catastrophic consequences.

Viruses cause measles, mumps, rubella and varicella (also known as chickenpox). They are infectious and are most common in children and young adults. Measles remains one of the leading causes of childhood death around the globe. Rubella is also dangerous for pregnant women, as it can cause miscarriage or harm to unborn babies.

‘We wanted to assess the effectiveness, safety, and long- and short-term harms of the MMR vaccines in this updated review which was last updated in 2012,’ explains lead author, Dr Carlo Di Pietrantonj in a press release.

This humongous study included the review of 138 randomised and non-randomised studies: 51 studies (10 million children) assessed how effective the vaccines were at preventing the diseases; and 87 studies (13 million children) assessed the association between vaccines and a variety of harms.


Effectiveness of vaccination

In terms of effectiveness, the review found:

  • Measles: One dose of vaccine was 95% effective in preventing measles. Based on the data analysed in the review, the number of cases would fall from 7% in unvaccinated children to under 0.5% in children who receive one dose of the vaccine. After two doses, effectiveness was similar at around 96%.
  • Mumps: One dose of vaccine was 72% effective in preventing mumps. This rose to 86% after two doses. From data analysed in the review. The number of cases would fall from 7.4% in unvaccinated children to 1% in children were vaccinated with two doses.
  • The results for rubella and chickenpox also showed that those vaccines are effective. After one dose of vaccine was 89% effective in preventing rubella, and one study found that after 10 years the MMRV vaccine was 95% effective at preventing chickenpox infection. If exposed to chickenpox, 5 out of 100 vaccinated children would catch it.

Safety of the vaccines

"In terms of safety, we know from previous studies all around the world that the risks posed by these diseases far outweigh those of the vaccines administered to prevent them," said Dr. Di Pietrantonj.

"In this review, we wanted to look at evidence for specific harms that have been linked with these vaccines in public debate - often without rigorous scientific evidence as a basis," he added.

The review summarises evidence from two studies with 1,194,764 children. Diagnosed cases of autism were similar in vaccinated and unvaccinated children.

“For every 100,000 unvaccinated children, we would expect 451 diagnosed cases of autism. For every 100,000 vaccinated children, we would expect about 419 diagnosed cases of autism.” the press release revealed.

This was contrary to the widely prevalent false claim linking vaccination and autism.

Two further studies with 1,071,088 children find no evidence for any association between the MMR vaccines and encephalitis, inflammatory bowel disease, Crohn's disease, cognitive delay, type 1 diabetes, asthma, dermatitis/eczema, hay fever, leukaemia, multiple sclerosis, gait disturbance and bacterial or viral infections.

"We judged the certainty of the evidence for the effectiveness of the MMR vaccine to be moderate. Although the studies that provide these data are not randomised, the effects are very large. The certainty of the evidence for the varicella vaccine, based on an RCT, was judged to be high," said Di Pietrantonj.

The review shows that MMR, MMRV and MMR+V vaccines are effective in preventing the infection of children by measles, mumps, rubella and chickenpox, with no evidence of an increased risk of autism or encephalitis and a small risk of febrile seizure.

“Existing evidence on the safety and effectiveness of MMR/MMRV vaccines support their use for mass immunisation. Campaigns aimed at global eradication should assess epidemiological and socioeconomic situations of the countries as well as the capacity to achieve high vaccination coverage. More evidence is needed to assess whether the protective effect of MMR/MMRV could wane with time since immunisation.” the reviewers concluded.


Vaccination coverage in India

In a paper on improving vaccination programmes in India, Gurnani and others highlighted the fact that India’s immunisation programme is the largest in the world, with annual cohorts of around 26.7 million infants and 30 million pregnant women (The BMJ 2018; 363:k4782).

“Despite steady progress, routine childhood vaccination coverage has been slow to rise. An estimated 38% of children failed to receive all basic vaccines in the first year of life in 2016. The factors limiting vaccination coverage include large mobile and isolated populations that are difficult to reach, and low demand from under-informed and misinformed populations who fear side effects and are influenced by anti-vaccination messages”, the authors said.

In October 2017, the Prime Minister of India launched Intensified Mission Indradhanush (IMI)—with an ambitious plan to accelerate progress and reach 90% full immunisation coverage in districts and urban areas with persistently low levels. The Mission identified several key messages helpful for future follow up.

The present Cochrane review which confirms the effectiveness of MMR vaccines is very useful in educational programmes for all stake holders.

 

Disclaimer- The views and opinions expressed in this article are those of the author's and do not necessarily reflect the official policy or position of M3 India.

Dr K S Parthasarathy is a freelance science journalist and a former Secretary of the Atomic Energy Regulatory Board. He is available at ksparth@yahoo.co.uk

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