ShareThisWhile long-ago swine flu shots or exposures may offer some immune advantage against the new H1N1 flu strain, scientists say a regular flu shot in the past few years provides no protection.
A study published by the Centers for Disease Control and Prevention used blood samples from 79 children and 280 adults who had been vaccinated against seasonal flu during one of past two winters.
Pre-vaccine samples found relatively high levels of an antibody that's thought to represent immune resistance to the new flu strain among older adults -- people in their 60s and older -- but not among samples from younger people.
There was no difference to the immune system response among younger people to the new flu, after they'd gotten one of the seasonal shots. However, there were slightly higher levels of the antibody in some of the older patients who had gotten a standard flu jab.
CDC officials stressed that the lab findings represent just one more clue in the mystery of why the new H1N1 flu has infected mostly younger people. Sixty five percent of more than 5,700 confirmed or suspected cases are among people between the ages of 5 and 24 years old. Only 1 percent of new flu cases were found in patients 65 and older.
"Normally, the elderly are more at risk from seasonal flu than younger people, but thus far the new strain seems to mostly have spared seniors,'' said Dr. Anne Schuchat, deputy director for science and public health programs and a leading flu expert at the CDC.
"The presence of this antibody can indicate that there is immune protection, but that's not definite,'' she told reporters in a telephone briefing from Atlanta Thursday. "We don't know if it offers any protection in actual people exposed to the virus."
Throughout the outbreak, government disease detectives had noted that the flu seemed to be spreading more readily and aggressively among younger people than the old. One explanation was that more young people had traveled to the epicenter of the swine flu outbreak in Mexico during spring break and vacations.
But the age pattern of flu infection has continued even as the virus has gone into widespread circulation in this country. This is making it seem more likely that some past exposure to a similar virus or to vaccines given against swine flu strains in 1957 and/or 1976 primed the immune systems of older people to fight to new strain.
The study findings-- drawn from samples stored by several government labs and vaccine makers in both Europe and the U.S. -- boost the likelihood that officials will need to use a triple or at least double needle strategy to protect high-risk patients from the different strains of flu that may be circulating in the fall.
Schuchat said if it turns out that some portion of the population already has some level of protection against the new flu virus, that could mean that those people might not need two separate doses of a vaccine," which would make the vaccine that we're able to produce go a lot further."
At this point, federal and international health officials haven't decided whether to try to produce millions of doses against the new flu or not. Even growing a seed stock from which to produce a vaccine has proved difficult. So even an experimental vaccine that can be tested in humans for safety and effectiveness is still weeks or even months away.
Another CDC official, Dr. Richard Jernigan, said that production of seasonal flu vaccine by several manufacturers here and in Europe is going smoothly so far and may allow for early shipment of at least some stocks earlier than normal -- before the customary start of the flu shot season in the September-October time frame.
"If possible, we do want to try and have an earlier rollout of the seasonal influenza vaccine simply for the reason to make it easier for an additional vaccine (to be administered), if that's the ultimate policy,'' Jernigan said.
E-mail Lee Bowman at bowmanl(at)shns.com.
(Distributed by Scripps Howard News Service, http://www.scrippsnews.com)
