Summary: Current vaccination policies are not sufficient to eliminate measles or prevent against future epidemics in the developed world, researchers report. Introducing compulsory vaccinations before entering school would allow the US, UK and Ireland to reach stable levels of herd immunity in the next ten years, thus helping to avoid future epidemics of the most lethal vaccine-preventable disease.
Source: Biomed Central
Current vaccination policies may not be sufficient to achieve and maintain measles elimination and prevent future resurgence in Australia, Ireland, Italy, the UK and the US, according to a study published in the open access journal BMC Medicine.
To successfully achieve and maintain measles elimination in these countries in the medium to long term, further country-specific immunisation efforts may be needed in addition to current strategies. Measles elimination has been defined as the absence of endemic measles transmission in a region or other defined geographic area for twelve months or longer.
A team of researchers at the Bruno Kessler Foundation and Bocconi University, Italy used a computer model to simulate the evolution of measles immunity between 2018 and 2050 in seven countries; Australia, Ireland, Italy, Singapore, South Korea, the UK and the US. The authors focused their analysis on countries with a routine two-dose measles vaccination programme and a high primary school involvement rate, but with different demographics and vaccination histories. The aim was to evaluate the effect of possible adjustments to existing immunization strategies and to estimate the proportion of people who may remain susceptible to measles in high-income countries over time.
The authors’ projections up until 2050 suggest that if current vaccination policies remain unchanged, the proportion of the population susceptible to measles would only remain below 7.5% in Singapore and South Korea, two countries which had high vaccination coverage in the past. Previous research estimated that the proportion of the population that does not have immunity (maximum susceptibility) needs to be 7.5% or less for measles to be eliminated.
In 2018, the proportion of the population susceptible to measles infection in the countries under study ranged from 3.7% in the UK to 9.3% in Italy (the only country where the proportion was found to be higher than 7.5%). In Australia, Ireland, the UK and the US, vaccination from routine programmes would need to continuously cover more than 95% of the population to keep the proportion of susceptible individuals below 7.5% until 2050.
Dr. Filippo Trentini, the first author said: “In recent years, we’ve witnessed a resurgence of measles cases even in countries where, according to World Health Organisation guidelines, elimination should already have been achieved. This resurgence is due to suboptimal vaccination coverage levels. In Italy, where measles incidents rates were among the highest, the government has made measles vaccination compulsory for children before they enter primary school. We investigated the potential of this and other policies to reinforce immunisation rates in seven high-income countries.”
Co-author Dr. Stefano Merler added: “Our results suggest that most of the countries we have studied would strongly benefit from the introduction of compulsory vaccination at school entry in addition to current immunisation programmes. In particular, we found that this strategy would allow the UK, Ireland and the US to reach stable herd immunity levels in the next decades, which means that a sufficiently high proportion of individuals are immune to the disease to avoid future outbreaks. To be effective, mandatory vaccination at school entry would need to cover more than 40% of the population.”
In Italy, the fraction of susceptible individuals by 2050 is projected to be 10%, even if coverage for routine vaccination reaches 100%, and additional vaccination strategies targeting both children at school entry and adults may be needed to achieve elimination.
Anne Korn – Biomed Central
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Original Research: Open access
“The introduction of ‘No jab, No school’ policy and the refinement of measles immunisation strategies in high-income countries”. Filippo Trentini, Piero Poletti, Alessia Melegaro and Stefano Merler.
BMC Medicine. doi:10.1186/s12916-019-1318-5
The introduction of ‘No jab, No school’ policy and the refinement of measles immunisation strategies in high-income countries
In recent years, we witnessed a resurgence of measles even in countries where, according to WHO guidelines, elimination should have already been achieved. In high-income countries, the raise of anti-vaccination movements and parental vaccine hesitancy are posing major challenges for the achievement and maintenance of high coverage during routine programmes. Italy and France approved new regulations, respectively in 2017 and 2018, aimed at raising immunisation rates among children by introducing mandatory vaccination at school entry.
We simulated the evolution of measles immunity profiles in seven distinct countries for the period 2018–2050 and evaluated the effect of possible adjustments of immunisation strategies adopted in the past on the overall fraction and age distribution of susceptible individuals in different high-income demographic settings. The proposed model accounts for country-specific demographic components, current immunity gaps and immunisation activities in 2018. Vaccination strategies considered include the enhancement of coverage for routine programmes already in place and the introduction of a compulsory vaccination at primary school entry in countries where universal school enrolment is likely achieved.
Our model shows that, under current vaccination policies, the susceptible fraction of the population would remain below measles elimination threshold only in Singapore and South Korea. In the UK, Ireland, the USA and Australia either the increase of coverage of routine programmes above 95% or the introduction of a compulsory vaccination at school entry with coverage above 40% are needed to maintain susceptible individuals below 7.5% up to 2050. Although the implementation of mandatory vaccination at school entry would be surely beneficial in Italy, strategies targeting adults would also be required to avoid future outbreaks in this country.
Current vaccination policies are not sufficient to achieve and maintain measles elimination in most countries. Strategies targeting unvaccinated children before they enter primary school can remarkably enhance the fulfilment of WHO targets.