It has always been a good idea to get a flu shot every year, but this season, it is particularly important, given the coronavirus pandemic. Symptoms of influenza and Covid19 often overlap and if we do catch the flu, it will weaken our defenses and render us more vulnerable to COVID-19 infection. There is even some suggestion that bolstering our immune defenses with the flu vaccine improves our resistance to coronavirus infection.

The influenza virus differs from the novel coronavirus in a number of ways but there are similarities, as well. Both are respiratory viruses, transmitted in a similar fashion, and quite contagious. Both can lead to severe illness and death. Influenza mortality varies from year to year, depending upon the severity of the outbreak, but on average, the case fatality rate is about 0.1%. (By contrast, COVID-19 mortality rates are still unclear, but are estimated to be up to ten times higher.) In the 2017-2018 winter season, for example, it is estimated that 61,000 people in the US died from influenza, while over 45 million people were infected. Other years have been even worse: the 1957 Asian flu killed 70,000 Americans and the 1918 influenza pandemic killed between 500,000 and 700,000 in the US!  Like COVID-19, older persons and those with chronic health conditions are at much greater risk. While COVID-19 appears to be less serious in young people,  influenza may be severe in children and pediatric mortality can be significant, especially for those in the first year of life.

Fortunately, most of the public health measures we follow, like wearing masks, social distancing, and hand washing will protect us from both influenza transmission and COVID-19.

There are two main types of the flu virus, influenza A and B. Unlike the coronavirus, which appears to be stable, flu viruses mutate frequently and change their outer membrane envelope proteins, which is why each year, new vaccines are required to fight the new emerging viral strains. Influenza is also a seasonal virus, emerging in winter months and seen only rarely during warm weather. Also, because flu viruses frequently mutate, seasonal outbreaks differ in severity–in past years, severe influenza epidemics have led to very high mortality, while other outbreaks are relatively mild.

Of course, we do not yet have a vaccine available for the prevention of COVID-19 infection, but we do have quite useful influenza vaccines, as well as medication for treatment and prevention of flu.

Medications For The Treatment Of Influenza Infection

Zanamavir ( Relenza) is an inhaler and Oseltamivir ( Tamiflu) is an oral medication. Both are useful for treatment and prevention (i.e. household contacts) of flu and are effective against both influenza A and B. Peramivir (Rapivab) is an intravenous formulation that works in a similar fashion and is used for hospitalized patients.

Baloxavir (Xofluza) is a single-dose oral medication used for treatment only.

Older medications, such as amantadine and rimantadine (Flumadine)are no longer used since they are only effective against influenza A and resistance to treatment is common.

All of these medications must be started within 48hours of symptom onset in order to be effective. While they are not “cures” for the flu, they shorten the duration and severity of the infection.

Influenza Vaccines

There are a number of different flu vaccines available for the 2020-2021 season.

Flu “shots” are composed of dead viral particles or recombinant ( manufactured in the laboratory using viral genome)viral proteins that contain “antigens” from influenza A and B surface proteins. Antigens are determinants that are recognized by our immune system so that we make antibodies that are protective.

Because the viruses are inactivated, they cannot cause flu in the recipient.

Flu vaccines are either trivalent (containing 2 antigens from influenza A and 1 from influenza B) or quadrivalent (2 antigens from each influenza  A and B).

Most of the flu shots that are being provided, whether from your physician’s office a pharmacy, or a hospital or clinic are quadrivalent. These are preferred since they contain 4 antigens.

Live, “attenuated” flu vaccine is also available. This product is quadrivalent and is administered via nasal spray. In effect, one is directly infecting the recipient with flu viruses that have been treated, so as to reduce their potency. This results in a rather potent immune response. However, mild illness frequently occurs. This vaccine is usually reserved for younger persons and is approved for ages 2-49. Because the viruses are live, it is contraindicated for pregnant women, immunocompromised individuals, and young children with asthma.

Older adults may opt for high-dose flu shots which contain 4 times the amount of antigen, compared to the usual vaccine dose. Senior citizens, in general, have weaker immune responses to vaccines and some evidence has demonstrated better antibody responses to high-dose flu vaccines, though proof that such vaccines prevent hospitalizations or reduce mortality does not exist. Previous high dose vaccines were trivalent; this is the first year that a quadrivalent high dose vaccine has been approved.

Side effects from vaccination are slightly more common in the high-dose preparations.

Another vaccine approved for those >65 years is an “adjuvanted” vaccine. This means that an agent (MF59-an oil-based emulsion) has been added to standard-dose vaccine to enhance the immune response.

Who Should Get Vaccinated?

Everyone over the age of 6months. Flu shots used to be recommended mostly for those over age 65, people with chronic illness, healthcare workers, and schoolteachers. But, especially now, with the COVID-19 pandemic, everyone should get vaccinated. There is no reason not to!!

When Is The Best Time To Get Vaccinated?

The optimal time for vaccination is right now: early October. Since flu season is generally from December through the end of February, if one gets vaccinated too early, the immune response may wane by late winter. It takes about 2 weeks for a response to vaccination, so it is best to get your shot by the end of October.

How Effective Is The Vaccine?

Every year is different since the vaccines are prepared in advance of the season and sometimes the antigens used are not optimized for the eventual seasonal outbreak. In general, flu vaccines are considered to be about 50% effective in preventing infection. But even if one does catch the flu, having received the vaccination reduces the severity of illness. Hospitalizations and deaths are much lower in vaccinated individuals.

What Are The Side Effects Of The Flu Shot?

Side effects are quite uncommon. Soreness at the injection site for a day or 2 does happen quite often, but this is minor. The adjuvanted and high dose vaccines are associated with more frequent or severe injection site soreness. Rarely, a day or 2 of fatigue, achiness, and even low-grade fever may result from vaccination. Very, very rarely, Guillain-Barre syndrome can result from a flu shot ( 1-2 cases per million vaccinations received).

Can I Get The Flu From The Vaccine?

No! Unless you have taken the live, attenuated vaccine by nasal spray, none of the available flu shots contain live virus, so you simply cannot contract flu this way. Some people have experienced adverse reactions to vaccination and have confused this with getting the flu from the shot. When documented respiratory infections seem to have developed following a flu shot, it is believed that the individual had already contracted a virus, which was incubating at the time the vaccine was administered.

Why Do We Need Annual Flu Shots?

Unlike some vaccines, which provide long-lasting immunity, the immune response to the flu vaccine lasts only about 6 months and then dissipates. Also, since the influenza virus mutates frequently, each season brings on different strains that the prior year’s vaccine likely does not cover.

I Am Allergic To Eggs. Does That Mean I Cannot Receive The Vaccine?

You can and should still receive the vaccine! Of course, if you previously experienced a severe allergic reaction to a flu vaccine, then the flu shot is contraindicated. But studies have shown that those with egg allergies can receive the flu vaccine without worry. Even though most of the flu vaccines are prepared by growing viruses in hen eggs, the amount of material in the final product is minimal. For those with severe egg allergy, flu vaccination can still be given, under observation in a doctor’s office.

Also, 2 products are prepared without the use of eggs: a recombinant flu vaccine (Flublok Quadrivalent by Sanofi Pasteur) and the cell culture-based product (Flucelvax Quadrivalent by Seqirus).

Can Immunosuppressed Individuals Receive A Flu Shot?

Absolutely! It is essential for those folks to be vaccinated. Some of the medications used for immunosuppression can impact the immune response to vaccination, so it is best to ask your physician how best to proceed. Sometimes, skipping a dose or two of your medication is advised in order to optimize your response to vaccination.

Can The Flu Shot Be Administered With Other Vaccines, Like Pneumonia Or Shingles?

Yes. Since these are all inactivated or recombinant vaccines, without live virus, co-administration of such vaccines is acceptable.

What About Mercury In The Vaccine?

Flu shots come in 2 versions: pre-filled syringes that contain no preservative and no mercury and multidose vials ( in which the provider draws each dose from a bottle containing up to ten doses into a syringe for administration). Multidose vials contain thimerosal as a preservative. These contain very small amounts of mercury. If you are concerned about this, make sure to receive your flu shot from a single-dose prefilled syringe.

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