MODEL SHOWS H1N1 VACCINE POISED TO BLUNT PANDEMIC IF GIVEN EARLY ENOUGH
As the H1N1 vaccine starts reaching cities in America this week, the question is how big of a difference will the vaccine cause in the overall pandemic? A study just published online (October 5) in the Annals of Internal Medicine examined the likely impact of the H1N1 vaccine on curbing the pandemic, preventing deaths, and cutting costs. The findings? Vaccination will likely have a major impact even if fewer than half of all people are immunized during October or November, according to an analysis of a mathematical model. The analysis suggested that over a wide range of viral reproductive rates and pandemic growth scenarios, vaccinating up to 44% of the population can be sufficient to slow widespread viral transmission by inducing herd immunity within the population and thereby shortening the pandemic.
“Absent serious vaccine side effects, vaccination earlier in the autumn is likely to be cost-saving and avert a greater number of deaths than later vaccination,” wrote Dr. Khazeni of the division of pulmonary and critical care medicine at Stanford (California) University and her coauthors.
Their analysis used an epidemic model for a hypothetical U.S. city of 8.3 million people similar to New York. The model involved several other assumptions, which in some cases were varied as part of a sensitivity analysis. For example, the basic model assumed that 1.5 secondary infections would be caused by each primary infection, that half of the symptomatic infected people would have a period of isolation, that the incubation time would be 3 days, and that symptoms would continue for 10 days.
Delaying the vaccination of 40% of the population until November would cut the benefit, with more than 45,000 quality-adjusted life years added and $282 million saved, compared with no vaccination. An immunization rate of 40% jibes with projections by the U.S. federal government to have 120 million vaccine doses for pandemic H1N1 available this autumn, enough to vaccinate 40% of the U.S. population. “Our finding that earlier vaccination saves more costs and averts more deaths may be most important for those areas in which there is more rapid growth of the pandemic,” the authors said.
Although public awareness about flu has heightened recently because of the attention paid this year to H1N1 and in past years to H5N1, vaccination rates for seasonal influenza have been “disappointing.” Seasonal flu kills more than 36,000 Americans annually, but fewer than 40% of high-risk adults aged 18-64 years received vaccination in 2008, wrote Dr. Farley and his coauthor. “Health care professionals must take advantage of this heightened public awareness to educate and vaccinate a larger proportion of the population, not only for H1N1 this season, but especially for seasonal influenza.”
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CDC ISSUES GUIDANCE ON H1N1 FOR PREGNANT WOMEN, ASTHMA PATIENTS
The first doses of H1N1 vaccine arriving in U.S. physician’s offices and clinics will be in the form of the live attenuated, nasal-spray vaccine, with supplies of inactivated, injectable vaccine scheduled to be available in mid-October. One disappointment is that physicians won’t be able to administer the nasal vaccine to two groups of people who CDC has targeted as high-risk individuals and who need early vaccine protection: pregnant women and patients with asthma. CDC issued new guidance on Oct. 2, that reiterated its position that people in both of these groups should receive the injectable H1N1 vaccine formulation only. Nasal-spray vaccine is not licensed for use in pregnant women, and it should not be used in patients with asthma because the spray can trigger wheezing. As always, the injectable vaccine shouldn’t be given to anyone with a life-threatening allergy to eggs or any other substance in the vaccine.
A secondary advantage to vaccinating pregnant women is that the protection they receive is also important once their children are born. Flu vaccine is not recommended for infants younger than 6 months; instead vaccine is aimed at household contacts and caregivers of these very young children. Flu vaccines are recommended for all pregnant women at any time during pregnancy.
The CDC information guide also highlighted that flu vaccines have not been shown to harm pregnant women or infants, that vaccine formulations with thimerosal preservative are safe during pregnancy, and that pregnant women can safely receive a seasonal flu and H1N1 vaccine on the same day, although different injection sites should be used. Pregnant women are not known to have an increased risk for side effects from the H1N1 vaccine.