The rapid rise of measles means children are forced to isolate for 21 days if they have not been vaccinated against the disease.
City councils warned parents after it emerged that there could be 160,000 cases in the capital alone.
Health officials say low uptake of MMR (measles, mumps and rubella) injections has increased the risk of a life-threatening infection.
Parents in London and surrounding counties were told that if a pupil became infected with measles, classmates and siblings who had not received both doses of MMR could be sent home and asked to isolate for three weeks.
It’s another blow for children who lost months of schooling during the pandemic.
City councils warned parents after it was learned that 160,000 cases could occur in the capital alone
Official data from October to December 2022 shows the areas most vulnerable to a possible measles outbreak: more than a quarter of children in London do not receive the MMR vaccine.
NHS England data released earlier this year shows MMR vaccine uptake plummeted to just 88.6 per cent for one dose in two-year-olds and 85.5 per cent for both injections among five-year-old children.
London’s Barnet Council was among those to send letters to parents warning that their children could face a three-week period of isolation from school if they are identified as a close contact of a measles patient.
“We are currently seeing an increase in measles cases circulating in neighboring London boroughs, so now is a good time to check that your child’s MMR vaccine, which not only protects against measles but also against mumps and rubella, is up to date,” he read.
‘Any child identified as a close contact of a measles case without satisfactory vaccination status may be asked to isolate for up to 21 days.
“Vaccinated children do not need to be excluded from school or daycare.”
He Telegraph reported that neighboring Haringey Council sent a similar letter.
The 21-day isolation period is based on guidance published in 2019 by Public Health England, predecessor to the UK Health Security Agency (UKHSA).
UKHSA told MailOnline that if a case of measles is detected in a child, health teams will work with schools to advise on next steps for children who have not received both MMR injections.
This may include an offer of MMR vaccination, administration of measles preventive medication to the child’s close contacts with vulnerable health conditions, and a possible exclusion for up to 21 days.
Siblings of an unvaccinated child who has been in close contact with a measles case may also be asked to isolate themselves.
Dr Vanessa Saliba, consultant epidemiologist at UKHSA, said: “Measles spreads very easily and can be serious, especially in vulnerable people such as babies, pregnant women and immunocompromised people.”
‘Cases are advised not to go to daycare, school or work until at least 4 days after the rash first appears to prevent them from spreading the infection to others.
‘Where there are cases or outbreaks of measles in nurseries or schools, the UKHSA Health Protection Team will assess the situation alongside the school and other local partners and provide advice to 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 minimize disruption to schools.”
The MMR vaccine, which offers lifelong protection against disease, consists of two doses and is 99 percent effective in preventing measles infection.
In Britain, it is first given when the child turns one and then again at three years and four months to offer the best protection.
Doctors are increasingly concerned that measles, long kept at bay by these vaccines, could return due to declining use.
National acceptance of receiving both MMR vaccines is currently around 85 percent, meaning about one in six school-aged children is not fully protected.
But vaccination rates are particularly low in London: just 74 per cent, meaning one in four children could be at risk.
Both national and regional figures are well below the target needed for herd immunity, where diseases have a low risk of spreading through the population, of 95 percent.
Acceptance of the MMR vaccine collapsed in the wake of a study by now-discredited doctor Andrew Wakefield that falsely linked the vaccines to autism.
Acceptance of MMR in England was about 91 percent before Wakefield’s study was published, but plummeted to 80 percent afterward.
While rates have recovered slightly, thanks to the concentrated efforts of health officials, a rise in anti-vaccine sentiment during the Covid pandemic is believed to have contributed to some parents choosing not to vaccinate their children.
Meanwhile, a total of 42 cases of the supermutated Pirola Covid variant have been found to have been detected in the UK, up from 36 last week.