With infection rates soaring, Labour says the Government has 'seriously misjudged' the crisis

Health experts are warning of a "surge" in flu cases this week as schools reopen and the UK returns to work in earnest after the Christmas and New Year break.

As deaths and hospitalisations from the disease continue to soar, the increase is expected to push the crisis towards an epidemic. The death toll from the flu now stands at 39 since October and the number in intensive care is already four times higher than the peak of last year's pandemic.

The Government is accused of making "serious misjudgements" and not doing enough to prevent the spread of the disease, following budget cuts to educational health advertising.

Some GP surgeries have run out the flu vaccination, which is being recommended for those vulnerable to the disease, such as asthmatics or pregnant women. Clinicians are also warning that since the vaccine takes up to 10 days to provide immunity it may now be too late for many, as the disease is expected to peak within the next fortnight.

John Oxford, professor of virology at St Bartholomew's and the Royal London Hospital, said: "We can expect to see a surge of infection next week as schools reopen and people go back to work; it's in the lap of the gods."

Flu-related intensive care admissions soared from 460 to 738 between Christmas Eve and 30 December. International evidence suggests that 10 to 15 per cent of those in intensive care may die, so we can expect 100 more fatalities. Of the 39 deaths from flu since October, 36 were from swine flu. Only one of the victims was over 65 and at least 15 were previously "healthy"; 11 were under 15, including four under five.

The Government is currently immunising only those in at-risk groups. But even those eligible for the vaccine report being turned away from surgeries because of low supplies and confusion over whether they qualify for it.

Fewer than half of all under-65s in at-risk groups, and just over two-thirds of those over 65, have been vaccinated. The confusion over who is eligible for the jab may have been caused by changes to those officially designated at risk. For example, "healthy" pregnant women, without other risk factors, were included in this category for the first time this autumn.

Parents have also complained that children aged under five have been denied the seasonal flu jab on the eve of their return to nursery this week, as GPs await instructions on who they can give it to.

Hundreds of parents were turned away from doctors' surgeries last week because government experts had not completed a review that could reverse an earlier decision advising against offering the vaccine to healthy under-fives. Young children have been among the worst hit by the virus and many parents have chosen to buy the vaccine privately.

The Department of Health re-launched a health advertising campaign yesterday. But the return of the "catch it, bin it, kill it" posters prompted criticism of a U-turn, as flu advertising had previously been pulled in budget cuts.

Labour's health spokesperson, John Healey, said: "We knew this would happen. We knew from our experience last year what we would face, but there have been serious misjudgements from the Government, and Andrew Lansley has been slow at every stage. There is mounting concern about the need for him to get a grip on this situation."

Mr Healey said the overall flu figures suggested the crisis was heading "towards an epidemic" – and the peak of the outbreak had yet to be reached. "With Britain going back to school, work and nurseries, the chances of those figures rising still further are much greater," he added.

In a reverse of last year's outbreak, when the onset of the summer holidays helped delay the spread of swine flu cases, the new term is expected to stoke the number of infections.

Meirion Evans, of the UK Faculty of Public Health, said: "Flu does spread more easily during term time because students or children mix together more."

Dr Evans warned that vaccination might well be too late for those going back to school. "It is late in the season to be getting vaccinated; with a lot of the flu in circulation now you run the risk that you've shut the stable door after the horse has bolted. If you get exposed to flu a few days after the injection it won't do much to help you."

Northern Ireland has the highest rate of infection in the UK, with 132 cases per 100,000 reported, compared with 124 in England and Wales, and 55.8 in Scotland. Health experts say the increase is unlikely to be related to the country's water supply crisis but a lack of running water will make it harder to maintain good hygiene, helping the spread of the disease.

Lorraine Doherty, Northern Ireland's assistant director of public health, said: "Our flu cases have increased uniformly throughout the province, so there's no evidence it is the water issue, but it is a challenge to maintain the same hygiene standards without running water ... I anticipate [infections] will further increase next week."

Although some GP surgeries have reported running out of the vaccine, the Department of Health insists there is no national shortage. A spokeswoman said: "GPs have already been asked to check their stocks. If they have run out, they have already been advised to work with neighbouring practices or their primary care trust to obtain further supplies. Manufacturers and suppliers still have stocks available for ordering."

Q&A: What it is and how to avoid it

What exactly is this 'flu' that has knocked so many sideways?

Take your pick from a sky-high fever, chesty cough, sore throat, aches, upset stomach, headache and runny nose: any of these symptoms can denote flu. Like last time, the majority of the serious cases are H1N1 – or swine flu. Of the 39 people to die so far, 36 had swine flu and only three had flu type B, typically a weaker strain of the virus.

How does H1N1 differ from 'normal' flu?

H1N1 is an aggressive strain of flu, which attacks the respiratory system and is capable of killing previously healthy adults. John Oxford, professor of virology at St Bartholomew's and the Royal London Hospital, says: "H1N1 is a very Darwinian virus. It is dominant and super fit, so it can push everything else out of the way and then off it goes.... It's like the beer that reaches places other beers can't reach – it gets much deeper into the respiratory system and makes some people very ill."

How many people are affected?

Everyone seems to know someone who has suffered, and indeed thousands are likely to get a mild version of the virus this winter. But with at least 738 people requiring intensive care so far and 39 deaths, for some people, catching the disease is far more serious. In England and Wales, 124 people in every 100,000 had confirmed or suspected flu infections between 20 and 27 December. In Northern Ireland, there were 132 cases in every 100,000 people, and in Scotland, 58.

Who should be most worried?

Normally the elderly are most at risk from flu, but H1N1 is disproportionately hitting the under-50s. Scientists believe this may be because older people developed immunity after being exposed to Spanish flu, which stopped circulating after the 1950s. Only one of the reported deaths since October was someone over 65; 11 were children under 15, including four under five. Pregnant women are up to four times more likely to get seriously ill. Those with existing respiratory problems are also at risk.

Is there a cure?

Tamiflu helps shorten its length and may curtail its spread, but it is not a "cure". It is also only effective if taken within the first 48 hours of symptoms.

What is the Government doing?

Too little, too late, many believe. The coalition withdrew campaigns on preventing the spread of germs in budget cuts last year, before reinstating them yesterday. Although vaccinations have been available to at-risk groups since the autumn – unlike last year, when vaccines only became available late-on in the pandemic – uptake has been low. Critics blame the lack of advertising.

How can you prevent catching it?

Those in at-risk groups – such as pregnant women and asthma sufferers – should get a vaccination as soon as possible. Otherwise, take basic hygiene precautions, such as using tissues for coughs and sneezes, and washing hands regularly. A healthy diet and regular exercise also help reduce the risk of infection.

What will happen now?

Since the latest count showed more than 700 people in intensive care, we can expect a sharp rise in deaths. International evidence suggests that 10 to 15 per cent of those in intensive care may die, implying 100 more fatalities. The virus is anticipated to peak within the next fortnight, but that will not be the last of it. Professor Oxford says: "It isn't going away. It will definitely be back next year. It won't extinguish itself like other viruses do."