“There’s nothing quite like flu in terms of the risk.”
- Tom Frieden, M.D., MPH, former director, Centers for Disease Control and Prevention
“Cover your cough. Wash your hands. Stay home if you’re sick. If you do get flu, there are antivirals you can talk to your doctor about that can prevent severe illness and help you stay out of the hospital.”
- Lynette Brammer, MPH, lead of Domestic Influenza Surveillance team of Centers for Disease Control and Prevention
The 2020-2021 flu season was astonishingly mild due in large part to precautions we took (and have now largely abandoned) to avoid getting COVID-19 such as the wearing of masks and social distancing. We are now on the brink of the 2022-2023 flu season (October to May) which some health experts warn could be exceptionally severe. The one thing we can all do to prepare is to get vaccinated.
In this week’s Germ Gems post, I discuss not only this year’s flu vaccine but also effective anti-viral medications for treating influenza. In addition, I discuss the development of a potential game changer—a universal flu vaccine.
Influenza vaccines and vaccine effectiveness. Influenza viruses have a genome composed of mRNA. (This is like the genome of SARS-CoV-2, the coronavirus that causes COVID-19.) Biologically, this means the genome is prone to mutation. Influenza vaccines for any given year are therefore based on predictions about the viral strains that are deemed most likely to cause upcoming flu or, in other words, are tailored to cover such “antigenic drift.” (For an excellent review of how this is done, see the article, “Influenza,” in the August 27, 2022 issue of Lancet.)
Flu vaccines are generally safe. Most are manufactured using viruses propagated in eggs and are quadrivalent (four components), containing an A(H3N2) and A(H1N1)pdm09 virus strain, and two representatives of influenza B virus lineages. (Because they contain a small amount of egg protein you’ll be queried about having an “egg allergy” before getting a flu shot. A newer version of the vaccine, called Flucelvax, however, is grown in animal cells instead of eggs.)
A vaccine’s overall effectiveness against seasonal flu is only about 40% to 60% and varies from season to season depending on how accurate the prediction is of what viral strains will appear. Nonetheless, mounting evidence suggests the vaccines are effective against life-threatening influenza in both children and in older adults who have underlying heart disease.
The Centers for Disease Control and Prevention (CDC) recommends that everyone six months of age or older without a contraindication such as an egg allergy should be vaccinated and that U.S. seniors get a “souped-up” vaccine, such as, Fluzone High-Dose or Flublok, which is made in insect cells instead of chicken eggs. Because the flu season lasts from October until May, the CDC also recommends vaccination in September or October. Other sources suggest waiting a month to optimize protection throughout the entire flu season.
The important thing is to get your flu shot. Many Americans are now eligible for the bivalent mRNA COVID-19 booster vaccine that gives added protection against recent Omicron subvariants. Getting a flu shot at the same time you get “jabbed” with your booster saves time without any recognized downside.
Treatment of influenza. There are two types of antivirals that are available and effective in treating influenza: Neuraminidase inhibitors (NAIs) and a polymerase acidic endonuclease inhibitor.
NAIs are a class of drugs that inhibit influenza A and B viruses and include oseltamivir phosphate (Tamiflu), zanamivir (Relenza) and peramivir (Rapivab). Tamiflu is approved for treatment of acute influenza in people 12 years of age or older who have been symptomatic for no more than 2 days. It is given orally, 75mg twice a day for 5 days. Zamanivir, which is inhaled, and Permavir, which is given intravenously, are for hospitalized patients.
Baloxavir (Xofluza), a polymerase acidic endonuclease inhibitor, is approved for people 12 years of age or older for prevention of influenza A and B. It is given as a single oral dose within 48 hours of developing symptoms.
Both Tamiflu and Xofluza have been shown to be safe and effective in reducing mortality and hospitalization as well as symptoms of the flu. But the important caveat for both medications is that they must be given within 48 hours of symptom onset. That is, timing is everything. So a nagging question is, how do you get treated in a timely manner with an antiviral agent?
Antiviral drugs are available for only two of the many viruses that cause upper respiratory tract infections: SARS-CoV-2 and influenza. Therefore it is important to know the main symptoms of influenza: fever, dry cough, muscle pains, sore throat, and headache. If you develop these symptoms, referred to as “influenza like illness (ILI),” then it is important to rule out COVID-19 by testing for it. This is because many of the same symptoms occur in people infected by SARS-CoV-2 or by influenza virus.
A rapid in-home antigen test for COVID-19 is the quickest way to rule in or out SARS-CoV-2 infection. If the test is positive, contact your health care provider for instructions on whether you’re eligible for and should take the antiviral drug Paxlovid.
If the COVID-19 test is negative, you also should contact your health care provider. This is because during the flu season if you have an ILI, treatment with an anti-influenza drug is indicated even without testing and is based exclusively on development of symptoms of an ILI. And while a test for influenza virus is available, waiting for the results delays implementation and thereby the effectiveness of treatment.
In contrast to the antiviral agents mentioned above, antibiotics (that is, drugs active against bacteria) are of no use in fighting a viral infection. More important, they’re considered harmful when given to patients without evidence of a concomitant bacterial infection.
Promise of a “universal” flu vaccine. According to reports from the World Health Organization, 290,000 to 650,000 people die of flu-related causes every year worldwide. Given the inadequate effectiveness of current seasonal influenza vaccines, it should come as no surprise that vaccine researchers have been working for decades on developing a “universal” influenza vaccine. The National Institute of Allergy and Infectious Diseases defines such a vaccine as having at least 75% effectiveness protecting all age groups for a minimum of one year against all strains of influenza A. (The National Academy of Medicine adds all influenza B strains and extends protection for three to five years).
Due to the major advances in vaccine technologies, such as mRNA platforms and delivery systems spawned by the COVID-19 pandemic, many researchers are optimistic that this goal can be achieved within a decade. (Given the recent, almost magical experience of developing and implementing two COVID-19 mRNA vaccines in a year’s time, one wonders if this couldn’t be accelerated?)
According to the News Feature “Researchers getting closer to a ‘universal’ flu vaccine,” in February, 2022 in the Proceedings of the National Academy of Science, “A universal influenza vaccine represents a game changer that could take the threat of both seasonal and pandemic influenza “off the table.” What a huge relief that would be for all of us!