New policies needed to prevent measles resurgence, study suggests

A recent study highlights the current vaccination policies and scenario to eliminate measles and prevent it from occurring in future in Australia, Ireland, Italy, the UK, and the US.

The study was published in the journal, 'BMC Medicine'.

To successfully achieve and maintain measles elimination in these countries in the medium to long term, further country-specific immunization 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 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 researchers focused their analysis on countries with a routine two-dose measles vaccination program 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 researcher's 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 per cent 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 needs to be 7.5 per cent 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 per cent in the UK to 9.3 per cent in Italy (the only country where the proportion was found to be higher than 7.5 per cent). In Australia, Ireland, the UK, and the US, vaccination from routine programs would need to continuously cover more than 95 per cent of the population to keep the proportion of susceptible individuals below 7.5 per cent until 2050.

Dr Filippo Trentini, the key researcher says, "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 immunization rates in seven high-income countries."

Dr Stefano Merler co-researcher 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 immunization programs. 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 per cent of the population.