Why are older people more susceptible to the flu?

It is currently the flu season.

In this autumn and winter, academics must eat well, sleep well, and exercise well to enhance immunity and stay away from influenza viruses. In particular, we should tell the elderly at home that in addition to getting the flu vaccine, they should also pay more attention to their own immune health.

Influenza is a contagious disease caused by influenza virus. Unlike the common cold, in addition to respiratory symptoms such as cough, sore throat, and nasal congestion, influenza can also cause systemic symptoms such as headache, high fever, muscle and joint pain, and even cause complications such as infectious pneumonia, bronchitis, asthma attacks, heart problems, ear infections, and acute respiratory distress syndrome.

Most people recover from the flu on their own, but the flu and its complications can sometimes be fatal . Although the flu vaccine is not 100% effective, it is still one of the effective ways to protect against the flu.

(Source: Photo Network)

Different people show different symptoms after contracting the flu, some are mild and some are severe. In addition to physical fitness, age is also an important factor. People over 65 years old have always been a high-risk group for influenza.

So, from a scientific perspective, why are older people more susceptible to the flu?

A joint research team from the University of Michigan and Temple University found some clues - as humans age, a lipid that controls inflammation seems to gradually weaken the lungs' immune defenses.

As a result, the lungs' first line of defense, alveolar macrophages, become impaired with age . Macrophages are immune cells that are found in the small air sacs, or alveoli, of the lungs and whose primary function is to attack external "invaders" such as influenza A virus (IAV).

Influenza A virus is a type of influenza virus, which includes multiple subtypes and can infect a variety of mammals such as wild birds, domesticated poultry, pigs, horses and humans, and cause influenza. Most of the famous influenza pandemics in human history were caused by influenza A viruses, including the Spanish flu in 1918, the Asian flu in 1957, the H5N1 avian flu in 2003, the H1N1 flu in 2009 and the H7N9 flu in 2013.

This study reveals key mechanisms by which elderly hosts become compromised to IAV and possibly other respiratory infections, and suggests potential new therapeutic or preventive pathways to protect them from viral respiratory diseases.

The related research paper, titled "Age-induced prostaglandin E2 impairs mito-chondrial fitness and increases mortality to influenza infection", was recently published in the scientific journal Nature Communications.

(Source: Nature Communications)

A previous study showed that when macrophages from old mice were transplanted into young mice, they looked young again.

In this regard, the paper's first author Dr. Judy Chen and her team speculated that perhaps something/substance in the lung environment causes these macrophages to be lost as the body ages.

Through experiments, it was found that a lipid immunomodulator called prostaglandin E2 (PGE2) can actually affect the ability of the elderly to resist influenza viruses. (PGE2 is a type of prostaglandin, mainly used to soften the cervix, induce uterine contractions, induce labor during childbirth, and can also stimulate osteoclasts.) With age, the content of PGE2 in the lungs will also increase significantly, and the increased PGE2 will in turn affect the overall health and production capacity of macrophages, inhibiting immune response.

The research team speculates that the accumulation of PGE2 may be another sign of the aging process. Aging can prevent damaged cells from dividing uncontrollably, and aging cells can no longer replicate.

To uncover the relationship between PGE2 and increased susceptibility to IAV , the research team treated aged mice with a drug that blocks the PGE2 receptor.

The results showed that compared with old mice that were not injected with this drug, the old mice injected with this drug had an increase in the content of alveolar macrophages and a higher survival rate in IAV infection.

In addition, the research team believes that their findings can be easily extended to other respiratory infections , such as the new coronavirus, because aging is also a prominent risk factor for severe symptoms of COVID-19. Moreover, the severity of COVID-19 is positively correlated with serum PGE2 levels.

Although the study demonstrated that blocking the PGE2 receptor can improve the host's defense against influenza, the research team also emphasized that they cannot rule out the influence of other age-related factors in the lungs, which may also impair the host's resistance to IAV , and other new research is needed.

In the future, they will continue to study the specific ways in which PGE2 affects macrophages and its potential role in systemic inflammation. "As we age, we are more susceptible not only to influenza, but also to other infectious diseases, cancer, and autoimmune diseases."

(Source: Photo Network)

Not only the elderly over 65 , but also children under 5 years old (especially those under 6 months old), pregnant women and women within two weeks of giving birth, people with weak immune systems, people with chronic diseases such as asthma, heart disease, kidney disease, liver disease and diabetes, and people who are obese with a body mass index (BMI) above 40 are also at high risk of influenza complications.

In terms of preventing influenza, in addition to getting the flu vaccine, good personal health and hygiene habits can also effectively reduce the spread of influenza , such as washing hands frequently (with soapy water or alcohol), avoiding touching the eyes and mouth and nose, covering the mouth and nose with a tissue when sneezing, avoiding close contact with patients, not going out when sick, and not spitting anywhere.

Reference Links:

https://www.nature.com/articles/s41467-022-34593-y

https://www.mayoclinic.org/zh-hans/diseases-conditions/flu/symptoms-causes/syc-20351719