Young people including teens are leading the coronavirus outbreak in an area at risk of lockdown, a council has warned.
Knowsley Council said more than half of fresh cases in South Liverpool are aged 15 to 24.
The area was named on a leaked list of UK areas most at risk of following Leicester into a local lockdown.
It comes as scientific experts issued a stark warning immunity to the virus may be lost in months as the race to find a vaccine continues.
One virologist commenting on the new UK study into Covid-19 antibodies warned young Brits are acting 'cavalier' about their role in spreading the virus.
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The elderly and medically vulnerable have emerged worldwide as the most at serious risk from the deadly virus.
But with fewer deaths among younger people, authorities have noted an apparent relaxed attitude to social distancing rules up and down the country as the lockdown eases.
The reason for the spike affecting young people in South Liverpool was not clear or outlined by authorities.
In a tweet on Sunday, Knowsley Council said young people aged 15-24 appeared to be driving new infections in parts of Merseyside.
The Mirror Online has approached the local authority for comment on the new cases.
Meanwhile, emergency coronavirus testing centres are being set up around the area to tackle the spike.
Public health bosses are concerned after the sudden spike in the south of the city as well as in areas including Knotty Ash and Halewood in Knowsley, according to the Liverpool Echo.
There have been around 30 cases of the virus in South Liverpool in the past fortnight, with half of them in people aged 15 to 24.
Belle Vale, Childwall, Woolton, Allerton and Hunts Cross were among the areas affected.
Dr Sarah McNulty, Director of Public Health in Knowsley, added: “I can’t stress enough how important it is to stay at home and get tested if you develop symptoms, particularly with lockdown measures easing and pubs and bars now reopening.
“It is so important that social distancing is part of your everyday life – you don’t know who has it and who could be spreading it, but if you’re within 2 metres of them for more than 15 minutes and they test positive, you will have to self-isolate for 14 days.”
Knowsley was named at the weekend in a leaked report obtained by The Observer, identifying the areas in England suffering spikes in infection.
The report is similar to a publicly available list issued by Public Health England weekly that identifies ten local authorities with the highest weekly incidence of coronavirus.
But the leaked list expanded on the weekly surveillance reports, showing a 'traffic light' system to signal risk.
Five areas in the report - including Blackburn with Darwen, Sheffield, Bolton, Knowsley and Carlisle - had been rated red for "daily exceedance".
However Leicester remained far and above the worst-hit, with a rate of 16.3 new infections a day per 100,000 people, according to a seven-day average to July 4.
By comparison, Knowsley's rate according to that list was 2.3.
Today, authorities in Liverpool are urging people to get tested as they try to contain the spike.
Speaking about the rise in cases, Matt Ashton, Liverpool’s Director of Public Health, told the Echo: “Everyone is at risk of Covid-19, but we know that there is a perception among younger people that they are less at risk.
“The easing of the lockdown means this is a really dangerous moment for case numbers, and we need people not to let their guard down and throw away all of the sacrifices we have made since March.
“We owe it to each other to take precautions and look after each other, regardless of their age.
“This is not just about your own individual risk, but the chances of you passing it on to your own family and friends, some of which may be in vulnerable groups and could become seriously ill."
He urged everyone to follow social distancing rules and get tested if they had symptoms so contract-tracing could begin and the outbreak could be stamped out.
Several areas named as hotspots including Leicester, and Merthyr Tydfil in Wales, have had major outbreaks at factories and food plants.
However in recent weeks police up and down the country have struggled to contain illegal raves and parties.
There have been fears revellers across all age groups won't maintain distancing rules as pubs reopen in England.
The King's College study struck a blow to theories populations may develop herd immunity if a jab against Covid-19 takes a long time to be developed.
The UK government abandoned what was claimed to be a herd immunity approach early in the pandemic following worldwide criticism.
The new research that emerged yesterday appeared to underline a flaw in such approaches, as it found people who recovered from Covid-19 may lose their immunity to the disease within months.
The research analysing virus patients at London's Guy's and St Thomas' Hospital suggested the virus could keep reinfecting people each season, just like common colds.
The study found levels of antibodies that fight Covid-19 peaked about three weeks after the onset of symptoms then rapidly fell, and that antibodies lingered longer following more severe cases.
Commenting on the study yesterday, University of Cambridge virologist Prof Jonathan Heeney told the Observer he is concerned some youngsters think having had virus symptoms and being less at risk of dying cleared them to continue a normal life.
He said: “I cannot underscore how important it is that the public understands that getting infected by this virus is not a good thing. Some of the public, especially the youth, have become somewhat cavalier about getting infected, thinking that they would contribute to herd immunity.
"Not only will they place themselves at risk, and others, by getting infected, and losing immunity, they may even put themselves at greater risk of more severe lung disease if they get infected again in the years to come.”