WHO issued a forecast for the Second Wave of H1N1 on last Friday, 28 August 2009. It was well written, clear and a bit sobering…
WHO has reached following conclusions after monitoring of outbreaks from different parts of the world:
- Countries in the northern hemisphere need to prepare for a second wave of pandemic spread.
- Countries with tropical climates, where the pandemic virus arrived later than elsewhere, also need to prepare for an increasing number of cases.
- Countries in temperate parts of the southern hemisphere should remain vigilant.
As experience has shown, localized “hot spots” of increasing transmission can continue to occur even when the pandemic has peaked at the national level.
H1N1 now the dominant virus strain
Evidence from multiple outbreak sites demonstrates that the H1N1 pandemic virus has rapidly established itself and is now the dominant influenza strain in most parts of the world. The pandemic will persist in the coming months as the virus continues to move through susceptible populations.
Any good news?
As a matter of fact yes there is.
- Close monitoring of viruses by a WHO network of laboratories shows that viruses from all outbreaks remain virtually identical. Studies have detected no signs that the virus has mutated to a more virulent or lethal form.
- The overwhelming majority of patients continue to experience mild illness.
- Although the virus can cause very severe and fatal illness, also in young and healthy people, the number of such cases remains small.
Large populations susceptible to infection
The trends are positive however remember that very large numbers of people in all countries remain susceptible to infection. Even if the current pattern of usually mild illness continues, the impact of the pandemic during the second wave could worsen as larger numbers of people become infected.
Larger numbers of severely ill patients requiring intensive care are likely to be the most urgent burden on health services, creating pressures that could overwhelm intensive care units and possibly disrupt the provision of care for other diseases.
Different from seasonal influenza
Current evidence points to some important differences between the pandemic virus and seasonal flu.
- The age groups affected by the pandemic are generally younger.
- This is true for those most frequently infected, and especially so for those experiencing severe or fatal illness.
- The most severe cases and deaths have occurred in adults under the age of 50 years, with deaths in the elderly comparatively rare.
- This age distribution is in stark contrast with seasonal influenza, where around 90% of severe and fatal cases occur in people 65 years of age or older.
A disturbing sign – Severe respiratory failure
Perhaps most significantly, clinicians from around the world are reporting:
- A very severe form of disease, also in young and otherwise healthy people, which is rarely seen during seasonal influenza infections.
- In these patients, the virus directly infects the lung, causing severe respiratory failure.
- Saving these lives depends on highly specialized and demanding care in intensive care units, usually with long and costly stays.
During the winter season in the southern hemisphere, several countries have viewed the need for intensive care as the greatest burden on health services. Some cities in these countries report that nearly 15 percent of hospitalized cases have required intensive care. Communities need to anticipate this increased demand for intensive care beds – hospitals could be overwhelmed by a sudden surge in the number of severe cases.
- Pregnancy is now consistently recognized as an increased risk and is well-documented across countries. This risk takes on added significance for a virus, like this one, that preferentially infects younger people.
- Certain medical conditions increase the risk of severe and fatal illness. These include respiratory disease, notably asthma, cardiovascular disease, diabetes and immunosuppression. WHO estimates that, worldwide, more than 230 million people suffer from asthma, and more than 220 million people have diabetes.
- Obesity, which is frequently present in severe and fatal cases, is now a global epidemic.
Higher risk of hospitalization and death
- Several early studies show a higher risk of hospitalization and death among certain subgroups, including minority groups and indigenous populations.
- In some studies, the risk in these groups is four to five times higher than in the general population.
- Possible explanations include lower standards of living and poor overall health status, including a high prevalence of conditions such as asthma, diabetes and hypertension.
Implications for the developing world
Such findings are likely to have growing relevance as the pandemic gains ground in the developing world, where many millions of people live under deprived conditions and have multiple health problems, with little access to basic health care.
As much current data about the pandemic come from wealthy and middle-income countries, the situation in developing countries will need to be very closely watched. The same virus that causes manageable disruption in affluent countries could have a devastating impact in many parts of the developing world.
SIMILAR — AND DISQUIETING – PATTERNS… H1N1 PANDEMIC VIRUS COULD GET NASTIER IN YEAR TWO
This caught my attention while reading reports over the weekend. A report issued from a well respected British virologist had good and bad news. The swine flu is unlikely to become more virulent as it spreads through the northern hemisphere this winter, but could re-emerge a year later in a more deadly form, said John Oxford, a professor of virology at Britain’s St Bartholomew’s and the Royal London Hospital.
“We should get through the winter relatively easily, I don’t think the virus will mutate before then,” “There will be more people in hospital and more deaths, but essentially it will be the same virus we have experienced in the summer, just more of it.” After winter has passed, however, the pressures of natural selection could favor the emergence of more deadly strains of the A (H1N1) virus, Oxford explained.
“For the moment, the virus is running around the world finding lots of young people and infecting them. It is doing very nicely, thank you, why should it change?”, he said by phone. “But once the virus has infected about a third of the world’s population — which is what we expect — it will find less ‘susceptible’. That is when mutants will have a selective advantage.”
It would be a serious mistake to think that once the impending flu season is over, the danger will have passed, he added. Oxford said he had just returned from Australia, where he met front-line doctors who were concerned about an emerging pattern in swine flu patients. Whether they are people in high-risk groups — the obese, pregnant women, asthmatics — or young adults with no underlying conditions, an alarming number of patients wind up in intensive care units. “One minute they are OK in a hospital bed, the next minute they are in intensive care,” he said.
Epidemiologists sifting through data from other countries have also found similar — and disquieting — patterns. French epidemiologist Antoine Flahault reported a 100-fold increase, compared to seasonal flu, in the number of swine flu deaths in Mauritius and New Caledonia attributed directly to the virus itself rather than secondary bacterial infections or underlying conditions. Many of those deaths were caused by acute respiratory disease syndrome (ARDS), which requires intensive-care treatment for an average of three weeks. Only 50 percent of ARDS patients survive.