Influenza disease is a viral disease that can cause epidemics in cold weather and is observed in the expected months and numbers each year, for which severe disease and loss of life rates can be predicted. Influenza cases, which start with sporadic cases at the end of summer, increase in our country in November, similar to northern hemisphere countries, reach a peak in January, and continue to decrease until April. During this period, influenza virus numbers are seen at rates exceeding other cold (such as the sniffles) viruses. Influenza virus caused the world's worst pandemic in 1918, and in two years between 1918 and 1920, sickened a third of the world's population, which was then less than 2 billion, resulting in the loss of life of an estimated 20 to 50 million people.

Even if the lowest estimates were correct, the Spanish flu took more lives than the ongoing First World War during the same period. At that time, the disease was thought to be caused by bacteria, not a virus, and there was no medication to use. The first antibiotic was discovered in 1928, but the first antibiotic and the first influenza vaccine came into use in the 1940s. Hygiene and appropriate health services were also inadequate.

Today, there is an effective vaccine and antiviral medications for influenza. Loss of life in epidemics is no longer high. The most recent influenza epidemic was the H1N1 epidemic, known as swine flu, in 2009. It was estimated that about 203.000 people lost their lives.

The Covid 19 virus entered the world agenda at the beginning of 2020. The virus infection, which started as an epidemic with a death rate of 3-4%, turned into a global epidemic that stormed through the world and stopped daily life, spreading rapidly in Europe in March, April, and May, and later in North America. The mortality rate was higher in most European countries. The coronavirus (Covid-19), which is the causative agent of the disease, is different from other coronaviruses that cause colds in humans and whose clinic is very well known, and what we have learned about the characteristics of the virus and the disease pictures in the body is still not sufficient. The epidemic continues in all countries.

How Can the Influenza Be Distinguished from the Coronavirus?

First of all, COVID-19 and influenza viruses cause similar diseases. That is, both cause respiratory disease, which manifests itself as a wide spectrum of diseases, including mild, moderate, or severe disease, and even loss of life.

The most common symptoms of both diseases are sore throat, tickle in the throat, dry cough, muscle, and joint pain, loss of appetite, abdominal pain, and diarrhea.

The transmission routes of the two viruses are also similar. Commonly, they are transmitted by contact, droplets, and surfaces.

As for their differences, the rate of transmission is a key point of difference between the two viruses. Influenza has a shorter incubation period and a shorter serial interval (the time between consecutive cases) than the COVID-19 virus. The incubation period for influenza is 2-4 days. The serial interval for the COVID-19 virus is estimated at 5-6 days, while the serial interval for the influenza virus is 3 days. This means the influenza can spread faster than COVID-19. 

In addition, in the first 3-5 days of the disease, the spread of the virus before the symptoms appear is the main transmission factor, while the transmission of the COVID-19 virus is thought to take place 24-48 hours before the onset of symptoms.

Children are very important driving forces in the transmission of the influenza virus in society. Preliminary data for the COVID-19 virus show that children are less affected than adults and the rates of clinical illness in the 0-19 age group are low. Preliminary data from domestic transmission studies in China suggest that children are more likely to be infected than adults. The susceptible age group is different in the two viruses. 

Data acquired so far for COVID-19 show that 80% of infections are mild or asymptomatic, 5% are severe infections requiring oxygen, and 5% are critical infections requiring respiratory support. These severe and critical infection rates are higher than those seen in influenza infection.

Those most at risk for severe influenza infection are children, pregnant women, the elderly, those with chronic diseases, and those who are immunocompromised. Our current information for COVID-19 shows that risk groups are the advanced age group, those with underlying diseases (such as high blood pressure, heart disease, chronic lung disease, and diabetes), and healthcare workers.

The mortality rate for COVID-19 appears to be higher than that of influenza, especially seasonal influenza. While it will take some time to fully understand the true mortality rate of COVID-19, the data we have acquired so far shows the crude mortality rate to be between 3-4%.

As a result, there are no very important clinical signs to distinguish between influenza and Covid-19, and it is not easy to distinguish between patients admitted to the hospital by questioning and examination. Although the loss of taste and smell and the development of severe shortness of breath in patients with pneumonia are defined as differences in Covid-19, it is difficult to make a differential diagnosis in this way.

While a patient who presented with the above-described common symptoms in the winter months before 2020 could be diagnosed with influenza without testing, testing will be required in the next winter season of 2020/2021. Because viral tests from nasal swab samples will be needed to distinguish between the two diseases. The main reason why we distinguish between the two diseases is that there is an effective treatment for influenza. There is still no effective, approved treatment and licensed vaccine for Covid-19 disease.

It is estimated that we will see many similar cases that will cause confusion between the two diseases and it will be difficult to distinguish them in the coming winter season, but there are also concerns that there will be cases that will undergo the two diseases together. For this reason, vaccination of risk groups against influenza, which has a very effective vaccine, will relieve both patients and healthcare workers. 

Do Influenza and Pneumonia Vaccines Protect Against Coronavirus? Do These Vaccines Have a Preventive Effect Against Covid-19?

The pneumonia vaccine is an effective vaccine against pneumococcus, a bacterium, and does not protect against Covid-19. The influenza vaccine, on the other hand, protects 4 of the influenza A and B viruses, which are very different viruses, but does not protect against Covid-19. However, it is recommended that people defined as the risk group should have both influenza and pneumonia (pneumococcal) vaccines, since it was published that super-infections with bacteria were also seen in patients during the epidemic in the Asian countries where Covid-19 first spread in January and February 2020 and the rate of death in these patients increased. In this way, it will be prevented from being confused with influenza and it will be ensured that the risk groups form a resistance against at least one disease.

Does Someone Who Gets the Influenza Vaccine Experience a Mild Coronavirus?

Influenza A and B viruses, which cause influenza, are different from the Covid-19 virus, and the person who gets the influenza vaccine creates antibodies only against the influenza virus. However, as emphasized in the article, protecting against influenza in the winter of 2020/2021, which will be a risky season, means providing confidence against one of the two diseases that have a common risk group. However, it may not cause those who get the influenza vaccine to experience a milder Covid-19 disease, but it is expected to reduce hospitalizations and loss of life due to the disease.

Who Are the Risk Groups for Influenza and Covid-19?

The entire society is susceptible to COVID-19. Healthcare workers are the riskiest occupational group in terms of encountering the virus. Males, people over the age of 50, those with chronic diseases (High blood pressure, Heart Disease, Diabetes, Cancer, COPD, Kidney Disease, etc.), and those living together in crowded environments are vulnerable groups in terms of COVID-19. The risk groups for influenza are those over 65 years of age and younger than 5 years of age (the highest risk being under 2 years of age), pregnant women, those living in nursing homes, those with chronic diseases (High blood pressure, Heart Disease, Diabetes, Cancer, COPD, Kidney Disease, etc.) and those who use aspirin.

Who Should Get the Influenza Vaccine? When Should the Influenza Vaccine Be Administered?

Individuals defined as risk groups should be vaccinated. Children in this group can be vaccinated if they are older than 6 months. In addition, it will be very important for healthcare workers to be vaccinated this year. Persons who should not be vaccinated are those who are allergic to the content of the vaccine (such as eggs) and those who have had a severe allergic reaction when previously vaccinated, as well as infants under six months.
The influenza vaccine should be administered two months before the expected epidemic time. Since vaccines are produced with new vaccine content every year, the introduction of vaccines to the market takes place usually in September-October. It is recommended that risk groups be vaccinated immediately within these dates. However, vaccination should not be abandoned when the time is missed, and risk groups should be vaccinated even at the beginning of the epidemic.