Flu shots protect against old flus, too

Did you get your flu shot? If so, you probably figured it would protect you against exposure to the three strains of influenza virus were deemed most likely to circulate this winter. But a new study in the journal Science reveals that the shot primed your immune system to defeat a much broader range of flu viruses, and it suggests a simple tweak to make it work even better.

Every year, 5 percent to 10 percent of adults and 20 percent to 30 percent of kids around the world become sick with the flu, according to the World Health Organization. For most people, that means a week or two of fever, cough, runny nose, headache and pain in the muscles and joints. But in 3 million to 5 million cases, the flu can cause more severe illness, including 250,000 to 500,000 deaths.

That’s why virologists put so much effort into developing the flu vaccine. It contains samples of weakened or deactivated viruses, enough to make the immune system swing into action and create antibodies. That way, if you encounter a real flu virus, your body will be prepared to fight it.

But influenza is a wily virus. There are three main types – A, B and C – and hundreds of subtypes. And these strains are constantly changing. Experts at public health agencies such as the WHO and the U.S. Centers for Disease Control and Prevention track the ones circulating in people and make their best guess about the three or four versions that are most likely to cause infection and put those strains in the flu shot (or flu mist). The better the match, the more protection, and vice versa.

“During years when the flu vaccine is not well matched to circulating viruses, it’s possible that no benefit from flu vaccination may be observed,” the CDC says.

But the new study in Science challenges that view.

An international research team found that the flu shot prompts the body to make antibodies against all of the flu viruses a person has encountered over his or her lifetime, not just the ones in the vaccine. In fact, the immune response “tends to be highest against strains encountered earlier in life,” they wrote.

The researchers came up with a name for this phenomenon: a “back-boost.”

Their first sign of its existence came from studying the blood samples of 69 people in Vietnam who were born between 1917 and 2005 and tracked for another study. All of them had given blood samples each year between 2007 and 2012. None had gotten flu shots, but they had been exposed to the flu (and sometimes got sick).

The researchers used the blood samples to create 3D computer models that they called “antibody landscapes.” These maps depicted the relationships among various flu strains, along with the strength of the antibody response to each one.

What these landscapes showed was that the strongest immune response was usually to flu viruses that were circulating when people were about 6 years old. Generally speaking, the older the virus, the bigger the response.

“Antibody levels against newly circulating viruses tended to be lower than those against strains circulating earlier in an individual’s lifetime,” the researchers wrote.

They called out the example of a study participant who was born in 1970 and got the flu in 2009. That infection caused the person’s immune system to make antibodies to versions of the 1968 Hong Kong flu strain, which had circulated in the subject’s youth but not in recent decades.

To check whether flu shots prompt this type of back-boost, the researchers piggybacked on two other studies. In both cases, volunteers gave blood samples, got a flu shot, and then gave another blood sample four weeks later.

In one of the studies, the vaccine protected against so-called Wuhan 1995 strains that had already been circulating for a few years. In the other study, the shot was built around a new flu strain that most people hadn’t encountered. However, the researchers discovered that this forward-looking vaccine prompted a “slightly larger” antibody response to Wuhan 1995 viruses than did the vaccine that targeted them directly.

The researchers couldn’t explain the biology behind this back-boost (though they described some of their theories in the study). However, they were pretty clear on the upshot of their finding: When designing a flu shot, you’re better off including new strains instead of old ones. Either way, you get protection against older flu strains. And if you guess right, you’ll get protection for new ones as well.

Talk to us

> Give us your news tips.

> Send us a letter to the editor.

> More Herald contact information.

More in Local News

A firefighter stands in silence before a panel bearing the names of L. John Regelbrugge and Kris Regelbrugge during the ten-year remembrance of the Oso landslide on Friday, March 22, 2024, at the Oso Landslide Memorial in Oso, Washington. (Ryan Berry / The Herald)
‘Flood of emotions’ as Oso Landslide Memorial opens on 10th anniversary

Friends, family and first responders held a moment of silence at 10:37 a.m. at the new 2-acre memorial off Highway 530.

Julie Petersen poses for a photo with images of her sister Christina Jefferds and Jefferds’ grand daughter Sanoah Violet Huestis next to a memorial for Sanoah at her home on March 20, 2024 in Arlington, Washington. Peterson wears her sister’s favorite color and one of her bangles. (Annie Barker / The Herald)
‘It just all came down’: An oral history of the Oso mudslide

Ten years later, The Daily Herald spoke with dozens of people — first responders, family, survivors — touched by the deadliest slide in U.S. history.

Victims of the Oso mudslide on March 22, 2014. (Courtesy photos)
Remembering the 43 lives lost in the Oso mudslide

The slide wiped out a neighborhood along Highway 530 in 2014. “Even though you feel like you’re alone in your grief, you’re really not.”

Director Lucia Schmit, right, and Deputy Director Dara Salmon inside the Snohomish County Department of Emergency Management on Friday, March 8, 2024, in Everett, Washington. (Ryan Berry / The Herald)
How Oso slide changed local emergency response ‘on virtually every level’

“In a decade, we have just really, really advanced,” through hard-earned lessons applied to the pandemic, floods and opioids.

Ron and Gail Thompson at their home on Monday, March 4, 2024 in Oso, Washington. (Olivia Vanni / The Herald)
In shadow of scarred Oso hillside, mudslide’s wounds still feel fresh

Locals reflected on living with grief and finding meaning in the wake of a catastrophe “nothing like you can ever imagine” in 2014.

The view of Mountain Loop Mine out the window of a second floor classroom at Fairmount Elementary on Wednesday, Jan. 10, 2024 in Everett, Washington. (Olivia Vanni / The Herald)
County: Everett mining yard violated order halting work next to school

At least 10 reports accused OMA Construction of violating a stop-work order next to Fairmount Elementary. A judge will hear the case.

Imagine Children's Museum's incoming CEO, Elizabeth "Elee" Wood. (Photo provided by Imagine Children's Museum)
Imagine Children’s Museum in Everett will welcome new CEO in June

Nancy Johnson, who has led Imagine Children’s Museum in Everett for 25 years, will retire in June.

Kelli Littlejohn, who was 11 when her older sister Melissa Lee was murdered, speaks to a group of investigators and deputies to thank them for bringing closure to her family after over 30 years on Thursday, March 28, 2024, at Snohomish County Superior Court in Everett, Washington. (Ryan Berry / The Herald)
‘She can rest in peace’: Jury convicts Bothell man in 1993 killing

Even after police arrested Alan Dean in 2020, it was unclear if he would stand trial. He was convicted Thursday in the murder of Melissa Lee, 15.

Ariel Garcia, 4, was last seen Wednesday morning in an apartment in the 4800 block of Vesper Dr. (Photo provided by Everett Police)
Everett police searching for missing child, 4

Ariel Garcia was last seen Wednesday at an apartment in the 4800 block of Vesper Drive. The child was missing under “suspicious circumstances.”

The rezoned property, seen here from the Hillside Vista luxury development, is surrounded on two sides by modern neighborhoods Monday, March 25, 2024, in Lake Stevens, Washington. (Ryan Berry / The Herald)
Despite petition, Lake Stevens OKs rezone for new 96-home development

The change faced resistance from some residents, who worried about the effects of more density in the neighborhood.

Rep. Suzan DelBene, left, introduces Xichitl Torres Small, center, Undersecretary for Rural Development with the U.S. Department of Agriculture during a talk at Thomas Family Farms on Monday, April 3, 2023, in Snohomish, Washington. (Olivia Vanni / The Herald)
Under new federal program, Washingtonians can file taxes for free

At a press conference Wednesday, U.S. Rep. Suzan DelBene called the Direct File program safe, easy and secure.

Former Snohomish County sheriff’s deputy Jeremie Zeller appears in court for sentencing on multiple counts of misdemeanor theft Wednesday, March 27, 2024, at Snohomish County Superior Court in Everett, Washington. (Ryan Berry / The Herald)
Ex-sheriff’s deputy sentenced to 1 week of jail time for hardware theft

Jeremie Zeller, 47, stole merchandise from Home Depot in south Everett, where he worked overtime as a security guard.

Support local journalism

If you value local news, make a gift now to support the trusted journalism you get in The Daily Herald. Donations processed in this system are not tax deductible.