Infants under a year currently account for 42.2 per cent of all admissions of children under 18 – compared with about 30 per cent in previous waves.
But paediatricians say parents can be reassured that few of the babies are severely ill, the average length of hospital stay was less than two days, few needed oxygen and there have been no reported deaths.
Early data from about 50 paediatric units in the UK was published by the ISARIC4C study this afternoon. It has been reported to the Government’s SAGE scientific advisory committee.
Of the 405 children and teenagers admitted to hospital with Covid between December 14 and January 12, 171 were less than a year old.
Professor Calum Semple, of the University of Liverpool, said: “Our study has shown that there has been an increased proportion of children being admitted in the last four weeks, associated with the onset of Omicron. This has been particularly driven by children under the age of one.
“The striking feature is that we are now seeing essentially 42 per cent of the children are under the age of one, when previously it was around about 30 per cent – a big step up.
“It does appear to be affecting children from the most deprived areas more than any other group.
“The big question is: are these children desperately ill or not? These are not particularly sick infants. They’re coming in for short periods of time for investigations.”
Professor Semple added: “Pregnant women can protect their babies through being vaccinated.”
ISARIC’s mission is to report on the “very earliest signals” from emerging data on Covid. Experts expect the figures to change over time. They say fears about a greater impact on children often emerge at the start of a new variant wave.
Russell Viner, professor of child and adolescent health at University College London, said the data suggested a rise in the number of babies being admitted with covid, even allowing for the increase in infections across all age groups driven by Omicron.
He said a rapid review by NHS England of 45 of the babies was “extremely reassuring”. Only one required intensive care, and not because of covid.
“Around half of them got no treatment at all,” he said. “They were in hospital for observation. A number of them got antibiotics.”
Many of the babies were displaying symptoms of fever and most were less than three months old.
Of 20 children aged 12-17 who required intensive care in the last month, none had been vaccinated.
Professor Viner said the high prevalence of Covid during the Omicron wave “may be pushing more babies into hospital because we are highly protective of young babies”.
He said: “The algorithms for NHS 111 and all of our advice suggest come to hospital and get antibiotics to make sure it isn’t major sepsis.
“I think we are seeing Covid behaving a bit more like the normal winter viruses we see in children. Parents are really experienced with that – just do what you always do with winter viruses in children.
“If you are worried, talk to your GP. If you are really worried, ring NHS 111 or take your child to hospital. Our hospitals are not full. Our children’s wards have space. The NHS is open.”
Dr Camilla Kingdon, president of the Royal College of Paediatrics and Child Health, said the ISARIC data provided a “very reassuring picture”.
She said: “We are not, on the shop floor, picking up any signals that we believe are concerning.
“We need to watch this space. But from around the country at the moment, the picture is a reassuring one.”
Professor Christina Pagel, of UCL, who was not involved in the research, said: “The absolute number of hospital admissions in children of all ages have been going up steeply since the Omicron wave (dashboard data) but this analysis provides a lot more detail.
“It is obviously concerning that significantly more infants under one are being admitted to hospital than previously.
“This cannot be explained just by vaccination status or high community prevalence, since the same is not true for instance of one- to four-year olds.
“It is possible that Omicron’s preference for upper airways is affecting young children more, even while it reduces burden in adults and older children and we urgently need to understand more about what might be causing this increase.
“The other notable finding from this study is that children from the most deprived areas are far more likely to be admitted and this has become significantly more pronounced with the Omicron wave: children from the most deprived fifth of households account for almost half of admissions.
“This is seen across all ages and is likely reflecting lower vaccination rates in teens from deprived areas, more exposure to infection and higher rates of other health condition making them more vulnerable to severe illness once infected.
“The disproportionate impact of the pandemic on more deprived communities has been long known but far too little done to address it.”
Dr Alasdair Munro, clinical research fellow in paediatric infectious diseases at the University of Southampton, said: “The vast majority of the adult population have now been immunised, and the majority of children over the age of five have either been infected previously, have been immunised, or both.
“The group with the lowest rate of immunity is children under five, and in particular, children under the age of one. This means we would expect a larger proportion of admissions to be among this population, which is what is demonstrated in this data.”