- Flu vaccination helps protect against severe illness and hospitalization.
- The flu shot is formulated months in advance based on research of potential strains.
- However, this means they may not ‘match’ all the flu viruses that ultimately circulate.
- It can take several months before the true efficacy of a seasonal flu vaccine is known.
It’s estimated that up to 11% of Americans catch the flu virus each year — with some experiencing more severe symptoms and requiring hospitalization.
Fortunately, vaccination can help defend against the disease. As there are many strains of the flu virus, the vaccine formulations are regularly revised to ensure they continue offering optimum protection.
“The composition of flu vaccines is reviewed annually by the Centers for Disease Control and Prevention (CDC),” explained Bernadette Boden-Albala, DrPh, director and founding dean of the Program in Public Health at the University of California, Irvine.
“Vaccines are updated to protect against the viruses that research indicates will be most common during the upcoming flu season,” Boden-Albala told Healthline.
However, flu viruses are constantly mutating. This means that, sometimes, the strains the vaccine is designed for aren’t the same as all those experienced during the subsequent flu season.
With the potential for virus ‘mismatch’, how long will it be before we know if this year’s shot is effective against the more prevalent flu types?
Unfortunately, it might still be a couple of months before experts have a better understanding.
In recent years, the flu shot has provided around 43% protection against disease. Although year-to-year that has ranged widely from 60% in the 2010-2011 flu season to 19% in the 2014-2015 flu season
This year flu cases are rising, but the peak of the season is yet to begin. And it’s not until more people become sick that experts can identify the most common strains and see how these line up against those used for the shot.
For instance, it wasn’t until mid-December of the 2021 flu season that researchers discovered the vaccine strains and circulating flu viruses didn’t fully align. However, because the flu shot is created to work against more than one strain, they stated that it still offered a level of protection.
As the flu season unfolds, data is continuously collected to shed light on the bigger picture. “Estimates for the 2022-23 flu season will continue to update through the rest of the year,” stated Boden-Albala. After this, “the CDC will produce a report on vaccine effectiveness.”
Experts say the flu shot can also help lessen symptoms for people who end up developing the disease.
Some believe that looking at countries in the Southern Hemisphere — which have their flu seasons earlier — can indicate how the virus might look once it arrives in the Northern Hemisphere.
For instance, the
However, “the reliability of this approach is debatable,” Matt Weissenbach, DrPH, senior director of clinical affairs at Wolters Kluwer Health, shared with Healthline.
This is primarily because it doesn’t take into consideration “confounding variables and limitations, such as missing data or external factors that couldn’t be controlled.”
That said, Weissenbach continued, “it’s still a worthwhile exercise when examining projections for overall incidence, timing, and season duration.”
As mentioned, the flu season in Chile began earlier than usual — and Weissenbach believes we may see a similar pattern in the US.
“We’re already seeing early season upticks in influenza transmission in some regions,” he stated. “It’s quite possible that we’ll see continued increases in early activity this season, as was noted in many of the Southern Hemisphere countries.”
By the end of October, over
The vaccine targets more than just one type of flu virus. “All flu vaccines in the United States are ‘quadrivalent’ vaccines, which means they protect against four different flu viruses,” revealed Boden-Albala.
She noted that the four viruses are:
- Influenza A(H1N1) virus
- Influenza A(H3N2) virus
- Two influenza B viruses
It takes about two weeks following vaccination for protective antibodies to develop in our immune systems, Boden-Albala explained. However, these antibodies don’t last forever — which is another reason why it’s advised to get a flu shot each year.
Numerous studies have explored how effectively flu vaccines protect against the virus. The CDC
Meanwhile, in Chile earlier this year, vaccination was
How the pandemic has impacted immunity
Boden-Albala shared that epidemiologists have predicted the upcoming flu season might be ‘bad’. This is partly because one of the main strains expected to circulate is linked to more severe symptoms.
But another reason more people could be impacted? The after-effects of pandemic-related measures, such as mask-wearing, social distancing, and staying at home.
“Community mitigation measures implemented throughout the pandemic are thought to have influenced influenza virus transmission to some degree,” stated Weissenbach.
Furthermore, Boden-Albala explained, these actions “have limited [our] exposure in the last few years to flu.” As such, “it’s expected that flu may be worse because of lower levels of circulating antibodies.”
The government has
