The flu season has come early to the US, in particular the West Coast.
In a typical year, flu cases begin to rise in October and November, with the increase first appearing in the South before it migrates North and then West.
But this year, health officials at the Centers for Disease Control and Prevention (CDC) say the pattern is very different.
Flu activity started to rise in the week ending August 8, data showed, and has continued to show a small but sustained increase.
In just two weeks from September 19 to October 3, the latest data available, the positivity rate, the proportion of flu tests that detect the virus, rose from 2.5 to 3.6 percent. At the same time last year, it was 0.6 percent.
Over the same period, flu-associated visits to the emergency department have also doubled from 0.3 to 0.6 percent of all ED visits. By this week last year, they accounted for 0.2 percent of ED visits.
By region, official data show that flu levels are rising on the West Coast, which is normally the last area in the country to record surging flu levels.
Dr Helen Chu, a respiratory infections specialist at the University of Washington, Seattle, said: ‘This year, it seems like we’re having a flu surge very, very early.’
Official data show that flu cases are rising earlier than usual and in the West of the country. (Shown above is an image of someone receiving a vaccine)
She told HuffPost: ‘Certainly in the Pacific Northwest and… in California as well, there has been an early rise in flu cases.’
It’s not clear what’s causing the earlier rise in flu levels, but experts have linked it to the main variant of flu – a mutated version of last year’s ‘super flu,’ called H3N2 subclade K – that is currently circulating.
Dr Amesh Adalja, an infectious diseases expert at Johns Hopkins, told Prevention: ‘The leading explanation is [we have] a new variant whose mutation lets it get past the antibodies people built from past infections and vaccines.’
He suggested that meant more people were susceptible to it, which meant the disease ‘spreads sooner’ than in previous years.
It was also not clear why flu levels were rising earlier than normal on the West Coast this year, but experts said where the infection starts spreading in the country every year is ‘variable.’
An earlier rise in flu cases does not necessarily mean that the flu season will be more severe, experts said, but it has led them to call for prompt vaccinations.
Dr Danielle Zerr, who leads the pediatric hospital division at Seattle Children’s, told the Washington Post: ‘[Flu cases] are about two months early [in this area].
‘The way flu is circulating now, you wanted that vaccine in you two weeks ago, if not a little before that,’ she added.
The CDC recommends the flu vaccine every year for people aged six months old and over, with ‘rare exceptions’.
In particular, the vaccine is recommended for those who are at higher risk of hospitalization or death from the flu, including adults aged 65 years and over and those with underlying health conditions that weaken their immune systems.
The above graph shows that the positivity rate – the proportion of swabs that detect the flu virus – is rising in the US
Studies show flu vaccines in previous years have been between 35 and 60 percent effective at preventing a serious illness from the flu.
Unlike last year, experts say that the shot has been updated to trigger protection against the H3N2 subclade K variant.
Influenza, commonly known as the flu, is one of the most common and highly contagious respiratory infections, impacting around eight percent of the US population each year.
The infection can cause symptoms such as fever, cough, sore throat, stuffy nose, headaches and fatigue, and can lead to more serious complications including pneumonia and influenza-associated encephalopathy (IAE), a severe brain dysfunction condition.
While most people recover within a week, some may develop complications such as pneumonia, which can be life-threatening and require medical treatment.
It’s for this reason that doctors recommend an annual flu vaccination, which provides protection for six to eight months, to help lower the chances of being infected.
In terms of other diseases, wastewater surveillance shows that COVID cases are ‘low’ nationwide and have remained flat for the past few weeks, while cases of respiratory syncytial virus, a virus spread via air droplets that causes flu-like symptoms, are ‘very low.’
This year’s flu vaccine was updated to trigger protection against both the H1N1 and H3N2 strains circulating in the US.
