Up to a third of children in some areas have been infected

Fergus Walsh | 16:54 UK time, Tuesday, 24 November 2009

It's been one of the big questions of this pandemic. Just how many of us in Britain have actually had swine flu?

Knowing that would be incredibly useful, as the bigger the proportion infected, the further we are into this pandemic and the less likely there will be a further sting in its tail.

The Health Protection Agency (HPA) has done blood tests of hundreds of children and parents connected to early school outbreaks.

With one school in south west England they tested around 500 people. They found that although around one in 10 children fell ill, three to five times as many got infected and developed antibodies.

After analysing this and other data relating to the number of children being seen by GPs, the HPA has now come up with these interesting estimates:

• Up to one third of children in swine flu hotspots (such as England and the West Midlands) have already been infected with the H1N1 virus.
• Across the UK up to one in five children has had had swine flu.
• About half of those who get infected show no symptoms.

This is all very reassuring. Professor Maria Zambon from the HPA said:

"We didn't get the pandemic that we planned for and you might say that we've been lobbed a soft ball. There hasn't been high case mortality, the virus is sensitive to drugs, and we've been able to make vaccine and roll it out. I am incredibly grateful that we are not dealing with a pandemic of H5 (bird flu)."

Professor Zambon said the virus had had a relatively low impact on older adults and that was probably explained by pre-existing immunity. The HPA has these estimates:

• For those aged over 50 up to four in 10 people have pre-existing protective antibodies to the H1N1 pandemic virus.
• If you are under 50 it falls to around one in 10 of the population.

The professor, who is an acknowledged world expert on flu, did utter a few words of caution. "Influenza is full of mystery and intrigue. It has lots of twists and turns" and she predicted that mutations of the swine flu virus should be expected. She also pointed out that there could still be a substantial outbreak of seasonal flu over winter.

WHO: Swine flu jab as safe as seasonal vaccine

Fergus Walsh | 16:56 UK time, Friday, 30 October 2009

Many readers of this blog may be about to get a letter from their GP offering them a vaccine against H1N1 swine flu, or will receive an invitation in the coming weeks, if they fall into specific at-risk groups.

If so, they may well be interested in the latest advice from the World Health Organization(WHO).

The experts who advise the WHO and governments about immunisation have said that the H1N1 pandemic vaccines appear to be as safe as seasonal flu jabs.

The Strategic Advisory Group of Exerts (SAGE) on immunisation met earlier this week to review both clinical trials involving several thousand volunteers and the ongoing mass immunisation campaigns being conducted in at least 14 countries where several hundred thousand doses had been administered.

Details of its decision were released by the WHO.

This is what it says about vaccine safety and the use of the vaccine in pregnant women:

"The experts reviewed early results from the monitoring of people who have received pandemic vaccines and found no indication of unusual adverse reactions. Some adverse events following vaccination have been notified, but these are well within the range of those seen with seasonal vaccines, which have an excellent safety profile. Although early results are reassuring, monitoring for adverse events should continue.

"Concerning vaccines for pregnant women, SAGE noted that studies in experimental animals using live attenuated vaccines and non-adjuvanted or adjuvanted inactivated vaccines found no evidence of direct or indirect harmful effects on fertility, pregnancy, development of the embryo or foetus, birthing, or post-natal development.

"Based on these data and the substantially elevated risk for a severe outcome in pregnant women infected with the pandemic virus, SAGE recommended that any licensed vaccine can be used in pregnant women, provided no specific contraindication has been identified by the regulatory authority."

At a subsequent briefing, Dr Marie-Paule Kieny, WHO Director of the Initiative for Vaccine Research said:

"All the reports received to date... have shown that the safety profile of this pandemic vaccine is good and is very similar to the one known for seasonal flu vaccine. Nothing special about adverse events has been noted.

Therefore SAGE has considered that in view of the particular importance to vaccinate pregnant women who are at significantly higher risk of severe adverse outcome following infection with a pandemic virus, especially in the second and third trimester of pregnancy, that these women can be vaccinated with any of the licensed vaccines."

Pregnant women and young people

I would like to quote another section of the SAGE advice as it highlights the increased risks facing both pregnant women and the young:

"Globally, teenagers and young adults continue to account for the majority of cases, with rates of hospitalization highest in very young children. Between 1% to 10% of patients with clinical illness require hospitalization. Of hospitalized patients, from 10% to 25% require admission to an intensive care unit, and from 2% to 9% have a fatal outcome.

"Overall, from 7% to 10% of all hospitalized patients are pregnant women in their second or third trimester of pregnancy. Pregnant women are ten times more likely to need care in an intensive care unit when compared with the general population."

What stands out for me is the greatly elevated risks among pregnant women.

Pregnancy leads to changes in the immune, respiratory and cardiovascular systems and it has always been a risk factor for seasonal flu, but nothing like the potential threat posed by this pandemic strain.

Bear in mind, though, that since the outbreak began, the number of deaths from swine flu has been very low compared to seasonal flu (which mostly kills the frail elderly). The latest global death toll is 5,700 up around 700 in the past week.

This can be partly explained by the start of the northern hemisphere flu season. But set that against the fact that many millions of people worldwide had been exposed to the virus (around 500,000 in Britain alone).

All these figures are estimates only, but they help in setting in context the level of risk. The availability of a vaccine means that this is now a preventable disease.

SAGE said both the pandemic and seasonal flu vaccines can be given at the same time. As with the UK recommendation, it said one dose of vaccine is enough to protect those from 10 years of age.

For those older than six months and under 10, it says data are limited and more studies are needed. The UK is giving two doses, spaced three weeks apart to those under 10, but only to children in at-risk groups.

But as I said in my previous post, it seems just a question of time before this is extended to all children. SAGE had this to say:

"Where national authorities have made children a priority for early vaccination, SAGE recommended that priority be given to the administration of one dose of vaccine to as many children as possible."

When you bear in mind that SAGE is chaired by Professor David Salisbury, who is also the head of immunisation at the Department of Health, it appears to be a further pointer towards an eventual move to the mass immunisation of all children in the UK.