Those Who Have Already Had the Flu May Have Some H1N1 Protection

On Monday, US researchers revealed that those who have repeated flu infections or repeated flu vaccines may have some protection already against the new pandemic swine flu. Researchers have found evidence that the humane immune system is capable of recognizing bits of the new H1N1 virus that are similar to older, distantly related strains of H1N1.

Alessandro Sette, director of the Center for Infectious Disease at California's La Jolla Institute said:

"What we have found is that the swine flu has similarities to the seasonal flu, which appear to provide some level of pre-existing immunity. This suggests that it could make the disease less severe in the general population than originally feared."

The study was published in the Proceedings of the National Academy of Sciences, and may help to explain why many older people are less likely to have severe cases of the disease.

Allison Deckhut-Augustine of the National Institute of Allergy and Infectious Diseases said:

"Adults may have some pre-existing immunity for H1N1."

Deckhut-Augustine noted that this does not mean that older people are protected against infection and stressed that people should still be vaccinated against H1N1.

Bejoern Peters and his colleagues at the La Jolla Institute looked a flu epitopes, or molecular markers or structers that the immune system recognizes, dating back two decades. What they found was that the immune system's T-cells can recognize "a significant percentage of the markers in swine flu."

Human's immune systems have two kinds of protection: antibody responses which can prevent an infection, and T-cells which fight an infection once it has already occurred. In studying H1N1 in adults, Peters and his colleagues discovered T-cell protection but not an antibody response.

What this suggests is that the T-cell response decreases the severity of the disease, but doesn't prevent it. Peters said that this effect could be cumulative, and may explain why those over 50 are less likely to get noticeable H1N1 infections.

Deckhut-Augustine adds:

"This may also suggest why children are more susceptible to severe infection and why they might need two boost. "They haven't been around as long and they haven't been exposed to different strains of H1N1 as long as adults."

The influenza virus is very prone to mutation and each year the circulating strains change slightly, which is why new vaccines must be formulated each year and why people can continue to catch the flu over and over again. The H1N1 strain currently circulating is a never-before-seen combination of swine flu viruses, mixed with human and avian flu genetic sequences.

However, the new H1N1 virus was found to be an ancestor of an H1N1 virus first seen in the 1918 flu pandemic that killed over 50 million people worldwide. Researchers found that the new strain shared 49 percent of its epitopes with older, seasonal H1N1 strains. They found that by using blood from healthy donors, T-cells could recognize 17 percent of the markers.