Pupils who have not had two doses of a jab that protects against Measles risk being told to self-isolate for three weeks, councils have warned.

Authorities in England have issued letters to the parents of school-aged children, urging them to check that their youngsters have had both doses of the MMR (measles, mumps, and rubella) vaccine.

Those who are unprotected risk being excluded from school for 21 days if a student at their school has the deadly infection, in a bid to prevent them becoming ill themselves. It risks another blow to children’s education after they were banished from classrooms for months during the pandemic.

This advice was first issued by the UK Health Security Agency (UKHSA) in 2019 but councils have flagged it to parents amid a spike in measles cases. 

Health chiefs have warned that London — which has the lowest MMR vaccine uptake in the country — is at risk of an outbreak that could hit up to 160,000 people.

London’s Barnet Council is one of three authorities that have sent letters to parents warning that their child could face a three week isolation period from school if they are identified a close contact of a measles patient. 

‘Currently we are seeing an increase in measles cases circulating in neighbouring London boroughs, so now is a good time to check that your child’s MMR vaccination – which not only protects your child against measles but also mumps and rubella – is up to date,’ it read.    

‘Any child identified as a close contact of a measles case without satisfactory vaccination status may be asked to self-isolate for up to 21 days. 

‘Children who are vaccinated do not need to be excluded from school or childcare.’

Hertfordshire County Council sent out a similar letter warning parents of unvaccinated children of the potential 21-day exclusion period.

This letter added: ‘Spending 15 minutes or more in direct contact with someone infected with measles is enough to catch the infection’.

A similar letter was sent by neighbouring Haringey Council.

These letters were sent out between June and July.  

The 21-day isolation period is based of guidance published in 2019 by the UKHSA in 2019. 

It states that if a measles case is detected, health teams will work with schools to advise on next steps for close contacts who haven’t had both MMR jabs.

This can include an offer of MMR vaccination, issuing preventative measles medication for close contacts of the child with vulnerable health conditions and potential exclusion for up to 21 days.

Siblings of an unvaccinated child who has been in close contact with a measles case could also be asked to self-isolate. 

However, officials have said this isolation is not as strict as those imposed during the Covid pandemic. 

Children would be banned from school and told not to mix with other children and those considered vulnerable — babies, pregnant women and those who are immunosuppressed. But they can still leave their homes for other activities. 

Health chiefs say that while it is disruptive, the three-week isolation prevents measles from taking off among children — which could see more become seriously unwell. 

Dr Vanessa Saliba, consultant epidemiologist at UKHSA said ‘Measles spreads very easily and can be serious, especially in vulnerable individuals such as infants, pregnant women and those who are immunocompromised. 

‘Cases are advised to stay off nursery, school or work until at least 4 days from when the rash first appears to stop them spreading the infection to others.

‘When there are measles cases or outbreaks in nurseries or schools the UKHSA Health Protection Team will assess the situation together with the school and other local partners and provide advice for staff and pupils.

‘Those who are not up to date with their MMR vaccinations will be asked to catch-up urgently to help stop the outbreak and minimise disruption in schools.’

The MMR jab, which offers life-long protection from the diseases, consists of two doses and is 99 per cent effective at preventing measles infection. 

In the UK, the first dose is given when a child turns one and a second dose is administered at three years and four months. 

Measles, which mostly produces flu like symptoms and a rash, can cause very serious and even fatal health complications if it spreads to the lungs or the brain. 

One in five children who catch measles will need to go to hospital, with one in 15 developing serious complications like meningitis or sepsis.

Part of what makes measles so serious is that it is highly contagious.

Health officials estimate nine out of 10 unvaccinated children will catch the disease if just one child in their classroom is infectious.  

Medics have been increasingly concerned that measles, which has long been kept at bay due to vaccines, could make a return due to declining uptake.

Uptake for both MMR jabs sits at 85 per cent in England, meaning roughly one in six children of school age aren’t fully protected.

This includes an estimated 102,000 children aged four and five.

But vaccination rates are particularly low in London at just 74 per cent, meaning one in four children could be at risk.

Other data suggests as many as four in 10 children may be unprotected in some specific areas of the capital.

Both national and regional figures are far below the target needed for herd immunity (95 per cent), which prevents the diseases from spreading throughout the population.

Uptake of the MMR jab collapsed in the wake of a study by the now discredited medic Andrew Wakefield, which falsely linked the vaccine to autism.

MMR uptake in England was about 91 per cent prior to Wakefield’s study being published but plummeted to 80 per cent in the aftermath.

While rates have recovered slightly, thanks concentrated efforts by health officials, a rise in anti-vax sentiment during the Covid pandemic is thought to have contributed to some parents opting not to get their children jabbed. 

Meanwhile it has emerged that a total of 42 cases of the super-mutated Pirola Covid variant have been spotted in the UK, up from 36 last week.