Swine Flu Continues to Camp Out in U.S. and Vexing Vaccine Questions Remain

JULY 24, 2009

The 2009 H1N1 influenza virus continues to spread in the United States, hitting particularly hard at summer camps, military academies, and other places where people from different locales gather. “It’s very unusual to have this much transmission of influenza during the [summer] season and I think it’s a testament to how susceptible people are to this virus,” said Anne Schuchat, head of the National Center for Immunization and Respiratory Disease at the U.S. Centers for Disease Control and Prevention.

Schuchat, who spoke at a CDC press conference, said the country now has 43,771 laboratory confirmed cases and 302 deaths. This is the last time CDC will report a specific number of cases, Schuchat said, noting that there likely have been “well over a million cases” in the country. For weekly updated information about the spread of the virus, she referred people to CDC’s FluView.

Some camps have given out the antiviral drug oseltamivir to healthy campers to prevent the spread of the virus, which violates CDC guidelines. “We’re really strongly recommending them for treatment rather than prevention,” said Schuchat, stressing that prophylaxis should be reserved for people who are at high risk for severe disease. Prophylactic use of the drug can increase chances of resistance developing, and supplies of flu antivirals are also limited.

The CDC’s Advisory Committee for Immunization Practices (ACIP) will meet on 29 July to discuss the main biomedical prevention against the virus, a vaccine. The Department of Health and Human Services (HHS) has yet to decide whether the government will recommend the use of a vaccine, but ACIP will help CDC plan how to distribute it, in case it is needed. In particular, ACIP will advise which populations should be first in line to receive a vaccine and which may require a “tiered” scheme if supplies are limited. Schuchat stressed that HHS Secretary Kathleen Sebelius “has announced that we are planning for a voluntary vaccination program in the fall, assuming availability of appropriate vaccine and that the virus hasn’t changed so substantially that a vaccine wouldn’t work.” She noted, too, that about 60% of Americans who CDC recommends should receive the seasonal vaccine opted not to take it this year.

A key question remains about vaccine supplies. Manufacturers have had low yields of viral proteins needed to make a vaccine, a problem that might increase the need for adjuvants, immune system boosters like water-and-oil mixtures. Adjuvants can stretch the amount of vaccine made from a given amount of viral protein and reduce the number of shots needed to trigger an effective immune response. The U.S. government has purchased adjuvants from two manufacturers. But when the U.S. National Institutes of Health earlier this week announced trials of vaccines, none included adjuvants. And regulatory issues remain, because no licensed flu vaccines in the United States contain adjuvant.

Schuchat assured that clinical trials with adjuvants “are planned” and said some manufacturers “will be doing trials.” But specifics remain vague. “I don’t actually have the details of how many trials with adjuvants and timelines for those trials, but there are definitely plans to look at the behavior of the vaccine when it is adjuvanted,” she said. This issue could prove critical, especially if the world faces a shortage of vaccine and other countries start looking to the United States for help.

—Jon Cohen