A new vaccine for the novel H1N1 influenza A ("swine flu") may not become available in the U.S. in time to protect the population against the peak of this season's flu epidemic, according to epidemiologists who are closely monitoring the spread of the flu outbreak.

"Although the new vaccine now in development is expected to work better than originally projected, it will still arrive too late to affect the full fury of the swine flu," said epidemiologists interviewed by the New York Times.

The experts predicted that the peak of the outbreak likely will come in October or November, and there will not be enough vaccine to protect the 159 million Americans who have been designated by health officials as the first to receive the vaccine. These are healthcare and emergency workers, pregnant women, people aged 6 months through 24 years, adults up to age 64 with certain pre-existing medical problems, and people caring for infants younger than 6 months old.

Risk of Swine Flu among People with HIV/AIDS

Dr. Susan Fernyak

There is little evidence to show that people infected with HIV are more at risk of getting H1N1 flu, said Dr. Susan Fernyak, director of communicable disease control and prevention at the San Francisco Department of Public Health. However, she emphasized that HIV positive individuals "should be advised to get the swine flu vaccination as soon as it becomes available to them." Health officials have also advised HIV positive persons to seek vaccination for the regular seasonal flu.

According to interim guidelines issued by the Centers for Disease Control and Prevention (CDC) and last updated in June, there is insufficient data available to know who is at most risk for contracting swine flu. HIV positive people --particularly those with low CD4 cell counts or AIDS -- can experience more severe complications from typical seasonal influenza, and it is possible that HIV positive adults and adolescents may also be at higher risk for H1N1 flu complications. So far, however, surveillance data have not shown that HIV infection is a risk factors for H1N1-related complications or death.

Only 1 Dose of H1N1 Vaccine May Be Necessary

Federal officials reported last week that a single dose of the new vaccine, rather than the 2 they had expected, likely will prove fully protective against H1N1 flu. This means that by November, there will be adequate supplies of the vaccine for those persons identified as first priority recipients.

Officials expect about 50 million doses of swine flu vaccine to reach government warehouses by October 15, and 20 million more doses to be ready each week thereafter until 195 million is reached.

Unfortunately, if the H1N1 flu epidemic peaks in late October, as some health officials expect, millions of people likely will be infected before the vaccine is available. "It would be bizarre for it to peak in January or February, the way seasonal flu does," said Dr. Marc Lipsitch, an epidemiologist at the Harvard School of Public Health and a consultant on flu epidemics to the President's Council of Advisors on Science and Technology.

Dr. Lipsitch said that the flu pandemics in 1918 and 1957 both peaked early. It is normal for the number of influenza cases to be "near zero" at this time of the year (mid-September), yet the CDC has already rated flu activity as "widespread" in 11 states, primarily in the southeast, but also in Arizona, Alaska, and Oklahoma. "Ninety-eight percent of those flu cases were the new H1N1 swine flu," said Dr. Anne Schuchat, chief of immunization and respiratory diseases at the CDC.

After the new vaccine is tested, supplies will be shipped to health centers, schools, and other vaccination sites. Recent vaccine studies suggest that most recipients will be protected after 8-10 days. Therefore, if the epidemic's peak comes in late October, millions of people are likely to become infected with the flu before the vaccine is widely available.

However, if a single shot turns out to be protective, and if the flu peaks in late December, things may turn out better. Federal officials said there was no way to tell whether the pessimistic or optimistic projections would be right, since flu peaks at different times in different regions each year.

"I can't tell you it's going to be too late for 'a lot' of people," said NIAID director Dr. Anthony Fauci, who is overseeing vaccine trials for the National Institutes of Health (NIH). "It's certainly going to be too late for some."

Swine Flu Effects Expected to Be Mild

Regardless of the timing of the peak of the pandemic in the U.S., most cases of the swine flu are expected to be mild. Although a few strains of the new H1N1 virus have been shown to be resistant to the antiviral drug oseltamivir (Tamiflu), they have not yet become widespread.

Dr. Fauci said last Friday that the trials he was overseeing confirm that a single vaccine dose usually conferred immunity in adults. In the elderly, only 50%-60% develop adequate immune response, he said, but that is "right in the ballpark" for seasonal flu shots in the elderly, since their immune responses are weaker than those of younger adults.

9/15/09

Sources

D McNeil, Jr. Vaccine Supply May Miss Swine Flu Peak. New York Times. September 12, 2009.

MS Bajko. HIV-positives advised to get swine flu vaccine. Bay Area Reporter. September 10, 2009.