Swine flu genetics suggest a vaccine is possible

Genetic sequences of the swine flu virus sickening people worldwide show remarkable similarities from country to country, suggesting that all the infections are from the same strain. The finding is a dose of good news for those seeking to make a vaccine against this novel strain of influenza, U.S. health officials reported May 1 during a press teleconference.

“All of the genes of all the viruses we’ve examined are 99 to 100 percent identical,” says Nancy Cox, chief of the influenza division at the Centers for Disease Control and Prevention in Atlanta. “This means it will be somewhat easier to produce an influenza vaccine.” The lab tested swine flu virus strains from six countries.

Cox said that while a decision to make a vaccine specifically targeting the new virus hasn’t yet been made, the agency is taking steps toward that goal with the expectation that the flu will continue to spread. Anne Schuchat, CDC’s interim deputy director for the science and public health program, reports that confirmed cases in the United States have now risen to 141 people in 19 states.

CDC also gave the first glimpse of the novel flu strain’s level of contagion. Early data on infections within families indicate a spread rate of 25 to 30 percent. Schuchat characterizes this rate as “fairly high” but on par with seasonal flu viruses.

Influenza comes in many strains, each a slightly different version of the flu virus. The new flu strain infecting people around the globe is unique in that, although it has a well-known surface protein combination, H1N1, the H in this protein pairing has swine origins. Whether this trait will give this strain of flu virus unusual characteristics remains to be seen.

Also still unknown is the new flu strain’s virulence, or capacity to cause serious or even deadly illness. To calculate this, scientists will need a better idea of the total number of people infected and, among them, the number who have died or required hospitalization.

The past season’s flu vaccine does not work against this new strain, but the strain does appear to be susceptible to some antiviral flu drugs. These drugs must be taken within two days of the onset of symptoms.

Meanwhile, developing a vaccine will take months, Cox says. “We estimate it will take three weeks to get a high-yield vaccine candidate virus. We’ve already started that process.” Scientists will then use parts of that virus and another virus to make a vaccine, a process that would take another eight to 10 weeks, she says. The goal is to produce a vaccine that induces an immune response against the target virus — in this case the novel flu strain — without causing disease in the vaccine recipient.

But the process could also take longer than a few months. The regular seasonal flu vaccine made every year takes about half a year to produce. How quickly this supplementary vaccine might be ready is unknown, says Steven Salzberg, a computational biologist at the University of Maryland in College Park. “We’re in uncharted territory. We have a process that takes six months. This is not that process.”

SN staff writer Laura Sanders contributed to this report.