The H1N1 Virus, Strains of Which Have Circulated for Decades, Could Come Back in a More Virulent Form 

GoogleNews.com, Wall Street Journal, May 28, 2009, by Betsy McKay  —  Over the next several months, the new H1N1 flu virus is likely to continue to spread around the world, reaching into the southern hemisphere along with winter, then possibly staging a resurgence in the northern hemisphere come fall.

Hundreds of thousands of people could fall sick, and some will die. Public health officials will scramble to minimize the damage, as governments and drug makers continue to invest millions of dollars in a potential vaccine.

Infections seem to be slowing in many parts of the U.S., according to the CDC. It hasn’t spread in most other countries as widely as it has in Mexico and the U.S. Many of those who have died had other health problems, such as asthma or heart disease. Unlike the viruses that created the most recent three flu pandemics, this one isn’t entirely new.

Introduced into the human population by the 1918 pandemic, the H1N1 virus circulated widely in various forms until 1957, when it was replaced in another pandemic by a new strain known as H2N2. The H1N1 virus re-emerged in 1977 and has circulated ever since, changing slightly every year. But it differs from the new H1N1 virus, which is made up of swine viruses, and hasn’t circulated in humans until now.

Already, there are signs that people over 60 years old with exposure to H1N1 viruses that circulated decades ago may have some immunity. And other mild H1N1 viruses haven’t mutated to become more virulent, says Peter Palese, chairman of the department of microbiology at the Mount Sinai School of Medicine in New York, calling this new form of H1N1 a “mellow virus.”


Bloomberg News

A worker packaged materials used to test for viruses, including H1N1. 

It “may be less likely to be a killer virus or a virus which is highly virulent,” says Dr. Palese.

But that doesn’t mean it can’t make people seriously ill or isn’t worth combating, pandemic flu scientists say. Flu viruses are notoriously unpredictable. It’s not clear whether this virus will peter out or return next fall. If it does return, officials can’t predict whether it will cause the same mild disease, or mutate into a more virulent bug that could strike with a vengeance — like the dreaded 1918 pandemic virus that resurfaced and killed 50 million people, by some estimates.

“That really terrible experience of 1918 is in our minds. But I can’t tell you whether this virus will cause a lot of disease, some disease or no disease here in the northern hemisphere next season,” Dr. Schuchat said.

Flu viruses regularly mutate or change by swapping genes with other flu viruses to outsmart the immune systems of their human hosts. Such changes, which ensure a virus’s survival, make it possible to catch the flu from one year to the next. They can also make a mild virus like the current H1N1 strain more virulent. CDC scientists are examining potential changes to the new H1N1 strain to see if any might create a virus that would cause more severe disease, says Dan Jernigan, deputy director of the agency’s influenza division.

“There are a lot of other conditions out there that have killed many more people in the last three weeks than this has,” says Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. “But this is not about what’s happening now. It’s about what could happen.”

In New York City, the health department announced Tuesday that two more people with swine flu had died, bringing the total to four. Of particular concern to health officials is that the disease is striking mostly younger people. The virus is making its way through New York schools at an energetic pace after more than a month, with five more closing Wednesday.

Age matters. About 64% of U.S. H1N1 infections have been in people ages 5 to 24, while just 1% are over age 65, the age group that normally gets hit hardest by the flu. Some are developing severe disease: about 37% of those hospitalized with H1N1 have been between ages 19 and 49, according to a CDC analysis of a portion of U.S. patients. Pregnant women and people with chronic health conditions have been at risk.

A similar pattern was seen in the 1918 pandemic, in which death rates were highest among young adults. That may be due at least partly to the fact that people over age 60 may have some immunity to the new virus, from exposure to older H1N1 viruses that are more similar to the new swine flu than the other recent H1N1 varieties, according to the CDC.

Unsure of the course the disease will take, officials are preparing for the worst. Over the next eight to 10 weeks, CDC and WHO officials plan to track the spread of the disease in the southern hemisphere, where winter and flu season are setting in. They are watching to see if the virus mutates as it mixes with other circulating seasonal flu viruses, becoming more virulent or resistant to antiviral drugs such as Tamiflu. Last winter, one variety of H1N1 developed such a resistance while the more recent version hasn’t so far.

The CDC has shipped kits to influenza laboratories in more than 100 countries to allow them to test for the new H1N1 virus. Among the questions that agency scientists plan to monitor are whether many people are hospitalized for long periods with pneumonia, whether the virus causes secondary bacterial pneumonia, and who is affected most — children or adults, primarily healthy people or those with underlying diseases, Dr. Schuchat said.

U.S. and global officials are also pushing ahead to prepare a vaccine against the H1N1 virus, even though they haven’t decided whether or not to go ahead with mass production of shots. The U.S. government said last week it’s setting aside $1 billion for clinical studies and the production of two bulk ingredients to be placed in a federal stockpile in case vaccine production goes ahead.

Alessandro Vespignani, a professor of informatics at Indiana University who has modeled scenarios for the spread of H1N1 flu, predicts a second wave would strike more than the hundreds of thousands of people he expects to be hit by the first wave. “It’s good we had the first wave,” he said. “It gives us time to understand more about the disease.”


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