What makes the K subclade different? Here’s what you need to know about the “superflu”

This winter’s flu season is being more severe than usual, largely due to the new variant of flu, subclade K, a specific version of the H3N2 strain, which is circulating in several countries.

Reports about a “supergripe” are multiplying, just in time for the holidays, and cases of respiratory diseases are increasing, in most countries in the Northern Hemisphere.

In the US, the Centers for Disease Control and Prevention (CDC) recently reported 11 hospitalizations per 100,000 inhabitants. In the United Kingdom, the National Health Service faces the worst pressure since COVID-19em 2022.

In Portugalaccording to the most recent report from the National Institute of Health Doutor Ricardo Jorge, were identified 1269 positive cases for the flu virus last week — and the .

Much of this situation has been attributed to the rise of a new variant of the strain H3N2 of the flu virus: the K subclade.

According to , subclade K emerged in the summer and, since then, has become the dominant form of influenza in several countriesincluding Japan, the United Kingdom and several North American states.

What is known about the K subclade?

Influenza viruses can, in general, be divided into four types, designated A, B, C and D, with the viruses being A and B are responsible for seasonal epidemics that occur every year. Subclade K is an influenza A virus. Specifically, it is a version of the subtype H3N2.

It is natural for flu viruses evolve over time: small mutations cause slight changes in the genetic makeup of the virus, in a process known as antigenic drift.

In the last year, a specific version of H3N2 has acquired several new mutations that make it genetically distinct of previous versions of the virus, leading to the emergence of a new subclade.

According to a recent WHO statement, these subclade K viruses present several changes in relation to viruses related to A(H3N2). Current epidemiological data do not indicate an increase in disease severity, although this subclade signals a notable evolution in influenza A viruses.

Why are experts worried?

Although there is no evidence that the K subclade is more severe than other H3N2-type viruses, experts have raised two concerns — one related to vaccines and another with its subtype.

How are influenza viruses in constantly changingthe flu vaccine must be updated every year. But the timing of the K subclade brought particular difficulties.

The vaccine was conceived before the appearance of the K subcladewhich raised fears that vaccines may not be a “good match” and that immunization does not necessarily translate into better protection against this strain of the virus, according to the CDC.

The evidence available so far suggests, however, that this may not be the case. The effectiveness of the vaccine varies from year to yeargenerally being between 30% and 60%, according to Vaccine Alliance Gavi.

The WHO notes that The effectiveness of the vaccine against the disease is unknowna, but that initial evidence indicates that reduces the likelihood of hospitalization.

Data collected in the United Kingdom suggests that the vaccine reduces, in children, the probability of going to the emergency room in 72% to 75%. The same data indicate that the vaccine is less effective in adultsbut it still reduces emergency room visits by 32% to 39%.

The second concern is the fact that the K subclade being an H3N2 virus. In general, these viruses can cause more serious conditions than other flu viruses, contributing to a particularly difficult flu season, with both young and old people at greater risk.

While some countries, including the United Kingdom and Japan, reported a flu seasonl unusually precociousthe CDC indicates that, in the USA, the calendar of flu activity is comparable to that of previous years.

But, as in other countries in the Northern Hemisphere, everything indicates that the K subclade is dominate.

Recent data from the CDC’s FluView report shows that influenza A accounted for 98% of flu cases reported by public health laboratories, of which 89.9% belonged to the H3N2 subgroup. Nine out of ten samples of H3N2 analyzed by the CDC are from the K subclade.

Portugal entered the flu season this month. In the last week of November, the Minister of Health, Ana Paula Martinswarned that the winter would be very harsh — with good reason.