There are many mutations of the virus and the one that you get may not be the same one that is covered by the vaccine for that year. However, there is some evidence that even if it is not an exact match, people who are vaccinated are better able to fight it and have milder symptoms.

Encourage them to do a home Covid test. Get a result in 15 minutes. Of course, the PCR test is more accurate but that is not as easy to do. The diseases have symptoms that can overlap so it is dependent on the person's presentation. There are many online symptom charts comparing Covid, Flu and Cold symptoms.

Wearing a mask in enclosed, public spaces and hand washing are helpful in slowing and preventing the spread of colds and flu. To protect myself and my loved ones, I got my flu shot, wear a mask in markets, etc. and am washing my hands more frequently. Just putting the odds more in my favor.

The flu can be spread by individual who have virus but haven't developed symptoms yet. The big difference in symptoms for the flu and the "common" cold is running a higher fever. Colds tend to have fevers that are less than 100.4F while the flu generally goes higher. Colds usually start with a sore throat and then develop nasal symptoms. Individuals with the flu tend to have moderate to severe fatigue. Since there can be overlap of symptoms between the illnesses and can vary from person to person, it can be confusing. The most common difference is usually that higher temperature in the flu.

Interesting question: The viruses are in those areas. When individuals are tested for the antibodies, levels are found in many children. Public health resources are not as available and testing/reporting limited. It simply isn't as reported. Also, malaria is prevalent in many areas and symptoms may be attributed to that wide spread (Africa) disease. I would also guess that better climate leads to less time in enclosed spaces and less opportunity for virus to spread.

Besides getting a flu shot, wash, wash and wash the hands. I wear a mask in enclosed spaces (I am older and at higher risk for a "Bad" outcome). Since you can spread the virus before you have symptoms, I don't want to feel responsible for getting family or friends sick. Especially since I have family with health issues.

Symptom wise, the flu tends to give a higher temperature (greater than 38 C or 100.4 F.). Colds usually start with a sore throat and have more nasal symptoms, head ache is common and there may be a cough. Flu has more muscle aches, non productive cough and that higher temperature. Since some of the symptoms overlap, there may be confusion in determining what a person has.

Not as long term but there is an increase in the number of heart attacks and strokes in the weeks after influenza. The body generates an immune response which can result in widespread inflammation that may be involved in this process.