Two people ill with meningitis in Reading have been confirmed as pupils at two schools.
The students - one from Reading Blue Coat School and the other at Highdown Secondary School and Sixth Form Centre - are receiving treatment, the UK Health Security Agency (UKHSA) said.
The UKHSA announced on Thursday that a sixth-form pupil at The Henley College in Oxfordshire had died earlier this week - and that it had identified a social network that connected the three young people.
Close contacts linked to all three are being offered antibiotics as a precaution.
The UKHSA has not given fuller details on what links the three young people.
It said one case had been confirmed as Meningitis B (MenB) and it was awaiting further testing results.
It confirmed the case was not the same strain as MenB outbreaks earlier this year.
Two months ago, two people died of MenB in Kent, linked to a nightclub in Canterbury, and in April, three young people contracted meningitis in Dorset.
The agency said it was sharing information about the infection with students and parents at all affected schools. It added that the risk to the wider public was low.
In a statement, The Henley College said its "thoughts and sincere condolences are with the student's family and friends at this extremely difficult time".
"We are supporting those affected within our college community and are following the advice and guidance given by the UK Health Security Agency," it added.
"Out of respect for the family, we will not be providing further detail at this time."
Highdown School and Sixth Form Centre's head teacher Laura Mathews confirmed it too had shared information with students and parents about signs and symptoms of meningitis.
"Our thoughts are with all those affected," she added.
Pete Thomas, the headmaster of Reading Blue Coat School, said it was "a concerning time for families and the wider community."
He added: "We are deeply saddened by the news of the death of a student at another local school, and our thoughts are with their family, as well as with all those affected during this difficult time."
Dr Shamez Ladhani, consultant epidemiologist at the UKHSA, told the BBC it was "really unfortunate" to have had three separate outbreaks in such a short space of time.
"This is a very rare disease but when it strikes it can be very lethal," Ladhani said.
He said the picture in Reading was an "evolving situation".
"Just like Kent was, just like Dorset... it is difficult to know where it is going to go from here," he said.
"Hopefully it will settle down. At the moment, every indication is that there is no increased risk to any of the students in Reading, but the situation is evolving and if that changes we will take action if needed."
Ladhani told BBC Radio 4's Today programme: "We have the strain from one of the three cases [in Reading] and we know that it is completely distinct to the one that caused the outbreak in Kent and the one that caused the outbreak in Dorset.
"We have identified a social network where these three are connected and we are almost certain that this is going to be the same strain.
"The fact that they have the infection means that we have the same preventative measure and will try and identify the contacts and protect them with antibiotics and vaccines."
Olivier Picard, chair of the National Pharmacy Association, said pharmacies in the area had "already seen a very significant increase in demand for vaccination against MenB from worried parents".
"Although pharmacies are now carrying more stock than when we saw the outbreak in Kent, this is having to be managed carefully and demand could well exceed what pharmacies currently [have]...," he added.
He urged concerned families to "closely follow" advice from the UKHSA.
There are about 300 to 400 cases of meningococcal disease diagnosed in England every year.
It is most common in babies, young children, teenagers, and young adults.
Meningitis symptoms can develop suddenly - and can include:
The UKHSA said young people should check they are up to date with vaccinations, including the MenACWY vaccine offered to pupils in Years 9 and 10.
It remains free on the NHS for people until the age of 25 but does not protect against all strains of meningitis.
The UKHSA said other strains, like MenB, can circulate among young people.
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