The confirmation of the circulation of the H3N2 variant of influenza A in Costa Rica comes amid a recent increase in cases.
However, according to health authorities and experts, this does not imply the emergence of a new virus or a change in the severity of the disease.
In recent weeks, the Ministry of Health reported 249 cases of influenza A in a three-week period and confirmed seven cases of the H3N2 subclade K variant, all with mild symptoms and no hospitalizations.
Known variant, but more transmissible
“Influenza A H3N2 is a known variant, but the one currently circulating has a high transmission capacity,” explained epidemiologist Juan José Romero of the National University (UNA).
According to the specialist, this behavior has already been observed in other countries. Major outbreaks were first reported in Asia and Europe, and later in North America and Latin America.
“It has been the predominant virus in recent outbreaks in Canada, the United States, and Mexico, and it was expected to circulate in Costa Rica as well,” he said.
Known variant, but more transmissible
“Influenza A H3N2 is a known variant, but the one currently circulating has a high transmission capacity,” explained epidemiologist Juan José Romero of the National University (UNA).
According to the specialist, this behavior has already been observed in other countries. Major outbreaks were first reported in Asia and Europe, and later in North America and Latin America.
“It has been the predominant virus in recent outbreaks in Canada, the United States, and Mexico, and it was expected to circulate in Costa Rica as well,” he said.
He also explained that, in the northern hemisphere, influenza outbreaks tend to intensify between December and February, and that this year the increase came earlier due to the high transmissibility of the variant.
In Costa Rica, the current situation remains within expectations, with several respiratory viruses coexisting.
“We are not seeing anything out of the ordinary for the country, where we have historically coexisted with rhinoviruses, RSV, adenoviruses, and influenza,” Romero said.
Symptoms
With regard to symptoms, Romero stressed the importance of differentiating influenza from other mild respiratory infections.
“For example, the common cold usually causes a runny nose, sneezing, and mild discomfort, but it does not generally cause fever or muscle pain,” he explained.
“Influenza, on the other hand, can cause fever, headache, general malaise, and muscle aches, which in some cases requires medical attention,” he added.
He also emphasized that influenza can cause pneumonia or facilitate bacterial infections that complicate respiratory symptoms.
Who is at greater risk of complications?
Although most cases are mild, the specialist reminded us that there are groups at greater risk of developing complications.
Among them are:
• Older adults
• Young children
• People with chronic illnesses
• Patients with compromised immune systems, such as those undergoing cancer treatment or living with HIV
In these groups, early monitoring and timely medical care are essential.
Vaccination
Romero insisted that the flu vaccine remains a key tool, even against variants such as H3N2.
“It is possible for a vaccinated person to get sick, but vaccination significantly reduces the risk of pneumonia, hospitalization, and severe illness,” he explained.
CCSS data reveal that, although the 2025 vaccination campaign achieved an overall coverage of 85%, only 32.3% of children in the target population received the vaccine, making them one of the most disadvantaged groups.
During this year’s campaign, 197,513 doses were administered to children under six months and under eight years of age, despite this being a highly vulnerable population.
Prevention
The virus is transmitted in the same way as other types of influenza and COVID-19, so prevention measures remain in place.
According to experts, the following is recommended:
• Cover your mouth when coughing or sneezing
• Wash your hands frequently
• Avoid contact with other people if you have symptoms
• Take special care to protect young children and older adults
“If a person is sick, the most responsible thing to do is not to expose themselves or others,” Romero concluded.
