When it Comes to Influenza Prevention, Physicians Should Be "All In"

What would it look like if the US were to experience another influenza pandemic on the scale of the “Spanish Flu” pandemic in 1918-1919? During his presentation, “Influenza and H1N1: Be the Local Expert,” Thursday at the 2010 AAFP Scientific Assembly, Richard E. Allen, MD, MPH, FAAFP, chair of the St. Mark’s Hospital Department of Medicine, and associate director of the St. Mark’s Family Medicine Residency, Salt Lake City, UT, said that hundreds of millions of people would be affected and we could see a replay of what happened back then, when every large gathering place was converted into makeshift hospitals to house the millions of people who were struck with influenza. The most recent influenza pandemic was the Influenza A (H1N1) pandemic of 2009, which involved the H1N1 “swine flu” strain. First isolated in Veracruz, Mexico, this strain caused more than 14,000 deaths worldwide, with a case fatality rate of 0.03%.

Influenza has been around a long time and has killed millions of people. The 1918 pandemic strain was particularly deadly, with a fatality rate of around 2.5% (compared to the Russian flu of 1890, which had a 0.15% fatality rate. In terms of deaths per annum, influenza has been deadlier than the Black Plague, the AIDS epidemic, and both world wars. In a mere two years, the Spanish flu killed 50 million people. Currently, there are 36,000 excess deaths per year in the US due to flu, 200,000 hospitalizations (and perhaps even twice as many as that), and 200 million sick days costing $500 billion annually in lost work and productivity. Deaths from influenza have actually increased since the 1970s, possibly because there is a larger percentage of elderly people in the population, but the fact is that the virus is also more potent than before.

Allen said that the reason that we have not been able to come up with something that can “knock out” influenza, ala penicillin and infection, is because influenza (an orothomyxovirus) has eight different negative-stranded pieces of RNA, making it difficult to develop a vaccine. He also noted that mutations in the virus cause antigenic drift (minor changes in the N or H antigens) that leads to epidemics and is the reason we require a new vaccine annually. Enough mutations over time can cause antigenic shift (major change in H), leading to pandemics. Allen said that “we’ll never be able to eradicate the flu, like we did with polio or smallpox, merely by vaccinating enough humans” because of the “huge reservoir of birds that can carry the influenza virus.” He said that “As long as we have birds in the world, we’ll have the flu and live with the danger of pandemic.”

What does all of this mean to the practicing primary care or family physician? It means that there is a common, communicable, and potentially deadly disease that these physicians must recognize and understand in order to protect patients and provide the best possible care. Allen noted that influenza is “well known for its abrupt onset,” as little as 1-2 days incubation after exposure to the virus. Identifying signs and symptoms include fever, myalgias, malaise, headache, sore throat and cough, flushing, and hyperemic oral mucosa. Allen said that diagnosing influenza is actually “not very hard during the right season.” One study found that during flu season, the presence of fever and cough made a diagnosis of flu 80% likely. There are several tests that can be used in diagnosis, including rapid antigen testing, which has only a 50% sensitivity rate. The RT-PCR test is the most sensitive and specific (Allen called it “the gold standard”), can return results in about six hours, and can distinguish between influenza A and B and identify subtype.

During influenza season, there are several groups of patients who should be tested, including outpatients with febrile respiratory illness who are at risk for complications, and inpatients who have acute febrile illness. At all times of the year, testing should be performed on health care institution workers, residents, and visitors who come down with flu-like symptoms.

There are two forms of influenza vaccines: the trivalent inactivated influenza vaccine (TIV) and the live attenuated influenza vaccine (LAIV). The LAIV is only indicated for healthy, non-pregnant patients age 2-49 years. Both vaccines contain the same strains of influenza (A: H3N2 and A: H1N1, as well as a B virus), with strains potentially changing from year to year. Studies have shown that the TIV vaccine is about 80% effective in adults if the strains are correct, and about 50% if not matched. TIV is about 65% effective in children, compared to about 80% for LAIV. Allen reminded the audience that 70-80% effectiveness “is actually pretty good,” and is bolstered by the fact that we retain immunity from year to year.

Several groups should take priority when receiving flu vaccines, including children 6 months to 18 years, adults older than 50 years, people who are in close contact with children under age 6 months, people who are in contact with high-risk patients, and persons at high risk (pregnant women, children on aspirin, immunocompromised patients, etc).

Although many patients (and, it should be said, some physicians and other health care professionals) still have fears regarding the safety of the influenza vaccine, studies have conclusively shown that it is safe for nearly all patients, including children, pregnant women and neonates, patients with chronic medical conditions, and immunocompromised patients. Allen said that physicians should be cautious with patients with egg hypersensitivity, severe febrile illness (mainly to avoid confusing the symptoms of illness with possible side effects from vaccination), or with a history of Guillain-Barre syndrome (GBS). Adverse effects associated with the flu vaccine include fever, malaise, and myalgia in children (but not in adults in most studies). The most common reported side effect is injection site pain. Some patient will experience hypersensitivity reactions, including immediate IgE mediated reaction, mild urticaria, and angiodema, although severe reactions are quite rare. Allen said that studies have shown that the incidence of adverse reactions from flu vaccine is about the same as injecting saline into your arm.

Although there are currently several antiviral medications for influenza, they are not very effective. Available products include amantadine, rimantadine, zanamivir, and oseltamivir. Allen noted that studies have shown that antivirals only reduce the duration of symptoms by about a day. Side effects from these medications include anxiety, insomnia, delirium, cough, and nausea.

Allen said that hand washing is still the best form of prevention for influenza, along with good respiratory hygiene practices (ie, use tissues when sneezing). Other population-based interventions in the face of an epidemic or pandemic include travel restrictions, avoiding mass public gatherings, school closures, screenings, and voluntary home isolation. Allen said that “social distancing” is also effective (eg, avoid public transit and face-to-face meetings, adopt flexible work hours, and use alternate greetings instead of handshakes).

In closing Allen reminded the audience that they cannot be “only half in” when it comes to influenza prevention; they must be fully engaged as physicians in support of influenza prevention interventions.

HCPLive wants to know:

What do you say to patients who are worried about the safety and side effects of influenza vaccines?

Do you agree that all health care professionals should be required to receive the flu vaccine?

Have you had positive experiences with antiviral medications for influenza?