Influenza epidemic in Israel: a healthy two-month-old boy died because of the disease

The situation in Israel fits into a broad global trend. According to data from the World Health Organization, the Northern Hemisphere is experiencing high flu activity, with positive test rates above 10% in large areas of North and Central America, Europe, Africa and Asia. In some regions, including Northern and Western Europe and Central America, the rate of positivity even crossed the 30% mark. Also in the world the dominant variety is K, similar to Israel.

Behind the alarming picture of the spread of the flu, the heavy workloads in clinics and hospitals and the high mortality is a relatively new player in the flu scene, the K substrain of the H3N2 influenza A virus, which has already been identified by health authorities around the world as a major cause of the outbreak.

The K strain was first identified in the summer of 2025, and since then has spread rapidly in many countries, mainly in Europe and East Asia. In recent months it has become dominant in North America and Israel as well. According to the Centers for Disease Control, most of the samples taken this season belong to this strain, a relatively rare phenomenon at such an early stage of the season.

The influenza virus is an enveloped RNA virus, with a spherical or elliptical structure, equipped with two central proteins that stand out from its surface. One is hemoglotinin, which is responsible for the virus adhering to the cells of the respiratory system, and the other is noramidase, which helps release the new viruses from the infected cell. It is the combination between these types of proteins that defines the subtype of the virus, for example H3N2. In strain K there were structural changes mainly in the hemoglobin region. These changes, even if they are tiny from a molecular point of view, can dramatically affect the way the immune system recognizes the virus, and its ability to infect humans.

Similar to other flu strains, strain K also passes mainly through respiratory droplets emitted by coughing, sneezing and talking. After penetrating the upper respiratory tract, the virus binds to the cells, penetrates them and takes over the cell mechanisms for its replication. The result is damage to the respiratory mucosa and an acute inflammatory reaction, manifested by high fever, muscle pain, weakness, headache and cough. Among populations at risk, the disease may be complicated by pneumonia, worsening of heart and lung diseases, and even death.

The K strain is believed to be more contagious because its mutations improve the ability of the virus to adhere to human cells, thus increasing the chances of infection. In addition, it is possible that the changes allow him to partially evade antibodies created by previous vaccinations or infections in past seasons.

It is still unclear whether the strain causes an inherently more severe disease, or whether the increase in the number of severe cases is simply due to the fact that the number of infected is particularly high. Experts emphasize that both options are being examined at the same time, and that the full picture will become clear only later in the season.

Influenza viruses are constantly changing. In every replication of the genetic material, mistakes may occur, some of which are meaningless and some of which give an advantage to the virus. This process, known as antigenic drift, is why the composition of the flu vaccine changes every year. More rarely, a deep and rapid change occurs, a sharp antigenic change, which could ignite a global epidemic. In the case of strain K, it is a drift and not such a jump, but even a gradual change may be enough to damage the suitability of the vaccine.

The current season’s vaccine was developed months before the K strain was identified, and is therefore not perfectly compatible with it. Despite this, experts emphasize that it still provides significant protection against serious illness and death, even if it does not completely prevent infection.