H1N1 EPIDEMIOLOGY

October 9, 2009 — The reported number of children younger than 18 years who have died from H1N1 influenza in 2009 since April reached 76 this week, which is close to the number of children who normally die each year from seasonal influenza, an official from the US Centers for Disease Control and Prevention (CDC) said today, but the H1N1 virus in 2009 has yet to run its course.

"It's only the beginning of October," said Anne Schuchat, MD, director of the National Center for Immunization and Respiratory Diseases at the CDC in a press conference. "It's hard to predict what will happen next, but we're pretty sure that [the H1N1 virus] will be here going forward. Unfortunately, we do expect more illness, hospitalizations, and deaths in the weeks ahead, particularly among pregnant women and children."

This week the CDC received reports of 16 children dying from confirmed cases of the H1N1 virus and 3 children dying from likely cases. Dr. Schuchat said the pediatric death rate is climbing again after peaking during the spring, followed by a dip during the summer.

The majority of children who have died have had underlying diseases that put them at risk for influenza-related complications, she said, but between 20% and 30% of these children were healthy.

In comparison, the number of children who have died each year from complications of seasonal influenza has ranged from 46 to 88 during the past 3 years, according to Dr. Schuchat.

New Studies Focus on Vulnerability of Children

The risk faced by children in the H1N1 pandemic was underscored by a study published online October 8 in the New England Journal of Medicine. Researchers, including some from the CDC, studied 272 patients who were hospitalized this spring with H1N1 influenza. Of those patients, 45% were younger than 18 years and 5% were older than 65 years.

Further stoking concern about protecting children from the H1N1 virus was a CDC report released today showing that 20.8% of children aged 5 to 17 years were vaccinated for seasonal influenza during the 2008–2009 influenza season. Public health authorities want to see higher immunization rates than this for the H1N1 vaccine, as well as its seasonal counterpart.

However, the public is still getting used to the idea of routine vaccinations for these children. Until 2008, the Advisory Committee on Immunization Practices, an expert panel that advises the Department of Health and Human Services and the CDC, had not recommended annual vaccinations for seasonal influenza for this age group. In 2008, however, the ACIP said that these children should begin receiving the vaccine, beginning in the 2008–2009 season.

Clinicians Can Vaccinate Nonpriority Patients if Vaccine Supply Is Adequate

The national effort to vaccinate children and the rest of the population against the H1N1 virus began this past Monday, just 5 days ago. As of yesterday, vaccine manufacturers had 6.8 million doses available for distribution, and state and local public health authorities had placed orders for 3.7 million doses, said Dr. Schuchat, adding that there is usually a lag between the 2 numbers.

The initial scarcity of the vaccine has prevented states from immediately conducting school-based immunization programs that would reach the vulnerable pediatric population, she said. "We don't have enough for a large-scale rollout." She predicted that as vaccine production ramps up, "we'll be in good shape in the weeks ahead." The CDC has projected that between 40 and 50 million doses of vaccine will be on hand by mid-to-late October.

Anticipating shortages of the H1N1 vaccine, the CDC has recommended that clinicians first immunize a priority group of patients that consists of pregnant women, individuals who live with or care for children younger than 6 months, healthcare workers in direct contact with patients, children aged 6 months through 4 years, and children aged 5 through 18 years with a chronic illness. There is no recommended order of priority within this group.

However, on Thursday the CDC issued guidance for clinicians that would give them the green light to immunize patients who do not belong to this priority group if they have an ample supply of the vaccine.

CDC recommendations on who should be first in line "are not intended to deny 2009 H1N1 vaccine to anyone who wishes to be vaccinated," the agency stated. "However, until local supply of, and demand for, 2009 H1N1 flu vaccine balances out, the decision regarding who should get vaccinated is one that should be made between the provider and the patient, weighing whether there are enough doses available for those at greatest risk for infection and serious complications as well as the likelihood that patients turned away will come back for vaccine at a later date."

N Engl J Med. Published online October 8. Article