Flu season’s almost here: Are you ready?

Influenza pandemics like the one we had last year are uncommon, and mounting an effective response was a difficult challenge. The pandemic hit early and hard. Physicians and the public health system responded well, administering a seasonal flu vaccine as well as a new H1N1 vaccine that was approved, produced, and distributed in record time. Before the end of the season, approximately 30% of the population had received an H1N1 vaccine and 40% a seasonal vaccine.¹

What happened last year

The influenza attack rate in 2009-2010 exceeded that of a normal influenza season and the age groups most affected were also different, with those over the age of 65 largely spared.² Virtually all the influenza last year was caused by the pandemic H1N1 strain.² Fortuitously, the virus was not especially virulent and the death rates were below what was initially expected. TABLE 1 lists the population death rates that occurred for different age groups.² Most of the more than 2000 deaths were among those with high-risk conditions.³ Those conditions are listed in TABLE 2.

There were, however, 269 deaths by late March among children, which far exceeded the number of deaths in this age group for the previous 3 influenza seasons.² For the most part, these higher mortality rates were due to higher attack rates, rather than higher case fatality rates. This is evident from hospitalization rates for children younger than age 5, which exceeded those of other age groups, as shown in FIGURE 1.

TABLE 1
2009-2010 Influenza death rates by age

TABLE 2
Individuals at higher risk for influenza complications (or who may spread infection to those at higher risk)

FIGURE 1
Cumulative lab-confirmed hospitalization rate by age group, 2009 H1N1, April 2009-February 13, 2010*

The task will be simpler this year
While it’s not possible to predict what will happen in the upcoming season, 2 developments should simplify the family physician’s task of adhering to official recommendations:

• Only 1 vaccine formulation will be available, and
• For the first time, the recommendation is to vaccinate everyone who does not have a contraindication.⁴

The vaccine for the 2010-2011 season will contain 3 antigens: the pandemic H1N1 virus, an H3N2 A strain (A/Perth/16/2009), and a B virus (B/Brisbane/60/2008).² The decision on which antigens to include is made 6 months in advance of the start of the next flu season and is based on information about the most common influenza antigens circulating worldwide at that time.

Immunization for all

This year’s recommendation to immunize everyone who does not have a contraindication is a major change from the age- and risk-based recommendations of past years. The universal recommendation is the culmination of the incremental expansions of recommendation categories that occurred over the past decade, which resulted in suboptimal immunization rates.¹ In 2009, only 40% to 50% of adults for whom the seasonal vaccine was recommended received it.⁵ While the annual influenza vaccine recommendation is now universal, those who should be specially targeted include those in TABLE 2. Most public health authorities believe children should also receive special emphasis because of the high transmission rate among school-age children and their home contacts. Next, of course, come health care workers, who should be vaccinated to protect ourselves, our families, and our patients.^4,6

Antivirals for treatment and prevention

There are 2 uses for antivirals to combat influenza: treatment of those infected and chemoprevention for those exposed to someone infected. Treatment is recommended for those with confirmed or suspected influenza who have severe, complicated, or progressive illness or who are hospitalized.⁷ Treatment should be strongly considered for anyone at higher risk for complications and death from influenza.⁷