Introducing compulsory measles vaccination at school entry in addition to current immunisation programmes, in many high-income countries including the UK, Ireland and the US, would allow them to reach stable herd immunity levels in the next decades, according to a new analysis. The research*, published today in BMC Medicine, found that current vaccination policies might not be sufficient to achieve and maintain measles elimination and prevent future resurgence in Australia, Ireland, Italy, the UK and the US.
Researchers from the Bruno Kessler Foundation and Bocconi University, Italy, explained that there has been a recent resurgence of measles cases – even in those countries where in theory, according to World Health Organisation (WHO) guidelines, elimination should already have been achieved. They developed a computer model that could simulate the evolution of measles immunity from 2018 to 2050 in seven high-income countries that have a routine two-dose measles vaccination programme and a high primary school involvement rate, but different demographics and vaccination histories: Australia, Ireland, Italy, Singapore, South Korea, the UK and the US. They noted that in Italy, where measles incidence rates were among the highest, the government made measles vaccination compulsory for children before they enter primary school, and they also wanted to look at the potential effect of this and other policies on immunisation rates.
They reported that unless current vaccine policies are changed, the proportion of the population susceptible to measles would remain below 7.5% – the estimated level of vaccine coverage needed for elimination – only in Singapore and South Korea, which in the past have had high vaccination coverage.
In 2018, they found, 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 above 7.5%). Their projection showed that in Italy, the fraction of susceptible individuals by 2050 will be 10%, even if coverage for routine vaccination reaches 100%, and so to achieve elimination there might need to be additional vaccination strategies targeting both children at school entry and adults.
Their model also showed that 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.
The authors commented: “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.”
*Trentini F, et al. The introduction of ‘No jab, No school’ policy and the refinement of measles immunisation strategies in high-income countries. BMC Medicine, 2019, DOI: 10.1186/s12916-019-1318-5