- Flu vaccination helps protect against severe illness and hospitalization.
- The flu shot is formulated months in advance based on research of potential strains.
- The CDC has announced that this year’s vaccine seems to be a “very good match” to circulating strains.
Officials from the U.S. Centers for Disease Control and Prevention (CDC) announced that the formulations of the flu shot this year are a good match for the current viral strains circulating in the country.
The news comes as flu cases have risen drastically in recent weeks.
It’s estimated that up to 11% of Americans catch the flu virus each year — with some experiencing more severe symptoms and requiring hospitalization.
“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.
According to the CDC, the research includes looking at which flu strains are affecting people before the main flu season and how they are spreading.
Looking at this year’s flu vaccine
Despite the potential for virus ‘mismatch’, the CDC announced this week that this year’s vaccine seemingly aligns with the circulating strains.
Dr. Rochelle Walensky, CDC Director, stated in a briefing: “We look in real-time as to how well we think the influenza match is to what’s circulating. And, right now, the good news is that it looks like it is a very good match.” According to CDC data most flu viruses being seen in tests are genetically similar to those included in this year’s vaccine.
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,” said Boden-Albala.
The four viruses are:
- Influenza A(H1N1) virus
- Influenza A(H3N2) virus
- Two influenza B viruses
According to CDC data, of the influenza A viruses seen in the US so far this year, 79% have been the A(H3N2) strain, while 21% have been A(H1N1).
In recent years, the flu shot has provided around 43% protection against disease.
However, year-to-year, that level has ranged widely: from 60% in the 2010-2011 flu season to 19% in the 2014-2015 flu season.
As the flu season progresses, experts will continue to get more information about the most common circulating strains.
“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.
Learning from other countries
When formulating flu shots, experts look at countries in the southern hemisphere to see what strains are circulating during their winter.
For instance, the CDC noted that, in Chile, where the flu season began far earlier than in most years in January, the primary strain circulating was a type of influenza A(H3N2) virus. The virus also started spreading earlier in the year than usual and resulted in more hospitalizations than during the 2020-21 flu season.
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.”
What to know about the flu shot
By the third week of November, nearly 155 million individuals in the US had received their 2022 flu shot.
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 estimated that, during the 2019-20 flu season, vaccinations prevented around 7.5 million flu infections and 105,000 flu-related hospitalizations.
Meanwhile, in Chile earlier this year, vaccination was associated with a 49% reduced risk of hospitalization from the A(H3N2) flu virus — the most predominant type being transmitted at the time.
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 stated everyone over the age of six months can get a flu shot, although in rare cases they are not advised for some individuals (such as those with certain allergies).
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