By Catherine Colquitt, MD
Flu season is now upon us, and we are bracing for another memorable year, based on CDC and World Health Organization (WHO) forecasts. Influenza vaccine was first produced in 1945, but due to constant antigenic shifts and drifts in the hemagglutinins and neuraminidases on the influenza virus lipid envelope, flu vaccine targets, and thus vaccine composition, changes yearly. Constant revision of the vaccine is believed to explain, at least in part, its underutilization by a flu vaccine-weary public.
Flu vaccine strain selection starts in February when WHO experts meet to determine which three or four strains of circulating virus will make the cut for the various upcoming annual flu vaccines. After initial and advanced data analysis, the final flu vaccine strains are set in April, and production, packing, and distribution begin to make ready for orders to be filled each August. Influenza is a transmissible disease, but flu is not as highly infections as, for example, measles, caused by the Rubeola virus. On average, a person with influenza may account for four additional cases of influenza as opposed to 17 additional infections attributable to a single measles case.1 The CDC’s just-released data on the 2018-2019 influenza season and vaccine coverage shows that during the flu season just concluded, 62.6 percent of U.S. children ages six months to 17 years received at least one dose of flu vaccine.2 This is a 4.7 percent increase in coverage over the 2017-2018 flu season. The coverage rate for the same age group in Texas was only slightly lower (61.8 percent). Nationwide the highest flu vaccine coverage was in Massachusetts (81.1 percent) and the lowest was in Wyoming (46 percent). Among U.S. adults ages 18 to 64, coverage with flu vaccine for 2018-2019 was only 45.3 percent, but represented a significant increase from 37 percent during the 2017-2018 flu season.
Many of our patients avoid influenza vaccine due to a commonly held belief that it is not a life-threatening infection or because they have been led to believe that the vaccine itself is unsafe or may transmit influenza. We try to impress upon our patients the importance of taking the yearly flu vaccine in order to prevent flu or mitigate the severity of influenza if they contract it. It’s also critical, but often lost on patients, that the healthy herd get flu shots to protect the extremely vulnerable few. This includes the very young and old, pregnant women, persons with heart disease (including congenital heart disease), chronic lung, liver, and kidney disease, cancer, diabetes, and other immunocompromising conditions or therapies.
When patients stiffen at the suggestion of the annual flu shot, I have also found it helpful to quote the astonishing 2017-2018 U.S. influenza mortality data—79,000 deaths. We also remind patients that use of the vaccine means fewer sick days taken and no household spread, and less out-of-pocket costs for clinic, urgent care, ER, or hospital stays. There are also medication costs, possible treatment of complications, such as post influenza pneumonia, and, appealing to their altruistic impulses, the responsibility of the strong to shield the weak when it comes to flu.
It’s also good to remind patients that they are infectious for 24 hours prior to the onset of flu symptoms and for five to seven days after symptom onset. The incubation period for influenza ranges from one to four days, with an average of two days.
For the 2018-2019 influenza season, vaccine coverage among healthcare workers was 78.4 percent overall, and physicians now exceed pharmacists in flu vaccine coverage (96.1 percent for physicians versus 92.2 percent for pharmacists per CDC). Nurses had 90.5 percent flu vaccine coverage last season and advanced practice providers were 87.8 percent covered last season. The CDC preliminary estimates are that for the season just ended there were 36,400 to 61,200 U.S. deaths from influenza (AT&T Stadium capacity is 106,681), in addition to 37.4 to 42.9 million cases of flu, 17.3 to 20.1 million medical visits, and 531 to 647 thousand hospital visits.3 For patients who argue that the vaccine is ineffective, experts (not yet published Advisory Committee on Immunization Practices 6/27/19) believe the flu vaccine to be 30 percent effective in preventing influenza-like illnesses and hospitalizations, which translates to prevention of 40 to 90 thousand hospitalizations.4
But perhaps the most important words for some of our vaccine-hesitant patients to hear is that we, along with our staffs and families, take our own advice and get immunized, too!
1. Influenza and the 2004 Flu Vaccine Shortage, 2005, Tim Brookes
2. CDC Flu Vaccine Coverage, US 2018-2019 Influenza Season
3. CDC Preliminary Disease Burden of Influenza 2018-2019
4. Prevention and Control of Seasonal Influenza with Vaccine, Advisory Committee on Immunization Practices, US 2019-2020 Flu Season