Health secretary Matt Hancock has said he is willing to look at "all options" to boost England's vaccination levels, including compulsory immunisation.
Mr Hancock told the BBC he did not want to "reach the point" of imposing jabs, but would "rule nothing out".
More than half a million children in the UK were unvaccinated against measles from 2010 to 2017, Unicef says.
In March, the head of NHS England warned "vaccination deniers" were gaining traction on social media.
- Minister targets anti-vaccination websites
- Mum of woman disabled by measles on responsibility to vaccinate
The health secretary was speaking after a report in The Times claimed almost 40,000 British parents had joined an online group calling for children to be left unimmunised against potentially fatal diseases such as tetanus.
And in England, the proportion of children receiving both doses of the Measles, Mumps and Rubella (MMR) jab by their fifth birthday has fallen over the last four years to 87.2%.
This is below the 95% said by the World Health Organisation (WHO) to be the level necessary to protect a population from a disease.
The UK was declared free of the highly contagious measles disease for the first time by the WHO in 2017.
But in 2018, it experienced small outbreaks, and in March this year there was a sharp increase of cases across Greater Manchester.
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