There is still a lot unknown about SARS-CoV-2 because it is a new virus. The flu and COVID-19 have similar symptoms, but they are caused by very different viruses, meaning our immune systems respond differently. We cannot use the flu as a model for things like seasonal effects, because we have seen that COVID-19 is not as strongly linked with seasons as the Flu is. We also know that they both spread through liquid droplets, but influenza is able to spread surface to surface better than SARS-CoV-2. I wish we could use Influenza as a model for SARS-CoV-2 because it would have let us get a grasp on the disease much faster, but unfortunately they are totally different viruses and act differently.

We have known for a while that influenza can transmit via surfaces. We call this fomite transmission. For example, if a person sneezes or coughs onto a desk and then another person touches the desk then rubs their eyes, it is possible to get the flu. This risk is fairly low (4.2% of infections in a 2018 study), but the risk is believed to be even lower for SARS-CoV-2.

We already have influenza tests! If you go to a doctors office presenting with Flu-like symptoms, they will likely run a test for influenza. The rapid tests, most commonly found in urgent cares, take about 10-15min and are 90-95% accurate. There is also an RT-PCR test that is very sensitive in detecting viral RNA, but takes more time. There are also Rapid Influenza Diagnostic Tests that are antigen based. These can be done at home, similar to the COVID-19 home test, but their accuracy is lower (50-70% accuracy).

Myocarditis, or inflammation of the heart muscle, can be caused by a number of viruses. When an infection is identified in the body, the immune system triggers an inflammatory response. Similar to a fire alarm, it is a signal to the body that something is wrong. This can be dangerous when it occurs in the heart because it prevents blood from being pumped. The influenza vaccine, however is not delivered to the heart. The immune inflammatory alarm will be triggered either in the muscle or nose where the vaccine is delivered. Swelling at the injection site is a common side effect, but inflammation of the heart is not. The Mayo Clinic promotes vaccination for those with heart conditions, because if you have a heart condition, you are at increased risk of myocarditis following an influenza infection.

>It's totally possible! Scientists have been working on this for years and have some promising candidates being tested in humans right now. Below is some more information that I compiled for another question and here is a good article on one of the universal flu vaccines.
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>The current influenza vaccines vaccinate against the active binding sight (head) of the hemagglutinin. This is on of the the spots that mutates every year. The
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>universal influenza vaccine vaccinates against the stalk of the hemagglutinin. This portion of the virus does not rapidly change. There are a number of universal vaccines in clinical trials. These clinical trials ensure the vaccine is effective and safe before it reaches the market. If the vaccines that are currently in clinical trials meet the high standards, we might see a universal flu vaccine in the near future.

The current influenza vaccines vaccinate against the active binding sight (head) of the hemagglutinin. This is on of the the spots that mutates every year. The universal influenza vaccine vaccinates against the stalk of the hemagglutinin. This portion of the virus does not rapidly change. There are a number of universal vaccines in clinical trials. These clinical trials ensure the vaccine is effective and safe before it reaches the market. If the vaccines that are currently in clinical trials meet the high standards, we might see a universal flu vaccine in the near future.

The 1918 influenza is called the H1N1 strain and it is still around today. The flu differs from COVID-19 in one big way. Influenza virus mutates very quickly, which is why we need a new vaccine yearly that covers for different strains. Luckily with Influenza, you can get some protection against similar strains because the mutations are usually small changes. SARS-CoV-2, on the other hand does mutate, but not as rapidly. We don't yet know how our immune systems are going to respond to different strains of SARS-CoV-2. There is some evidence that previous infection with omicron can protect against other variants, but this is still under investigation.

The influenza vaccine is a trade off, like many things in our life. Scientists try to predict the strains that most people will be exposed to during the flu season and put those into the vaccine. For each strain added, we increase the cost of production and more importantly, each strain increases the load on your immune system. More strains might result in multiple shots needed, which decreases the number of people who get fully vaccinated. Or it could cause side effects, similar to what we have seen with the SARS-CoV-2 vaccine, which will decrease the number of people who get the yearly vaccine. Luckily, scientists are working on a universal influenza vaccine. This type of vaccine would vaccinate against a protein on the influenza virus that doesn't change. This would mean protection from more strains, as well as less frequent vaccination.

In response to your second question, I do not know of any positive purpose the influenza virus serves on an individual person basis. Historically, the 1918 influenza pandemic may have helped bring WWI to a close, at the cost of many lives. The flu hit the front lines across Europe in the first wave of infection. Influenza weakened and cut the numbers of fighting forces, leading to a need for more diplomatic tactics. I am not sure this is exactly a positive outcome because millions of people died from complications related to the flu, but it did help end a global war.

Influenza is a tricky virus to vaccinate against because it rapidly mutates and has multiple strains circulating in one year. Our ability to predict these strains is improving, but it is still a prediction. We are improving the number of strains we can vaccinate against. The first influenza vaccine only vaccinated against H1N1, where as this years influenza vaccine protects against 4 strains.

Unfortunately, as we are seeing this year, the flu did not disappear. The measures taken to prevent COVID-19, such as masking, hand washing and social distancing, are also great ways to prevent influenza. Additionally, during the 2020-2021 flu season, arecord number of influenza vaccines were distributed. Throughout history, it is common to see a decrease in a disease with the rise of another disease. Historiansrefer to these as disease cycles and they have had major impacts on human history.

Back in 1945, the push for the flu vaccine was similar to what we are seeing with the SARS-CoV-2 vaccine today. In 1918, the world was hit with a massive influenza pandemic that killed more than 20 million people world wide. By 1945, we had an influenza (H1N1) vaccine available for the general public. Unfortunately, the flu is a rapidly mutating virus, meaning that we see various strains dominating each year and some can turn into pandemics. All we can do is try to predict which strains will be prevalent and vaccinate against those in a yearly vaccine. In short, the answer to your question is that there has been a global push for influenza vaccination in the past, put there isn't currently a push on the level of SARS-CoV-2 vaccination because we haven't seen a flu pandemic on the level with COVID-19 since 1918.