A recent study has found that being infected with influenza – which infects humans – may give you immunity that will defend you against bird flu if you become infected with it.
The study was conducted by researchers from the Vaccine Innovation Center, La Jolla Institute for Immunology, in the United States, and was published in the magazine (mBio) on December 23, and Newsweek wrote about it.
According to the World Health Organization, there are 4 types of influenza viruses: types A, B, C, and D. Influenza A and B viruses circulate and cause seasonal epidemics of disease in humans. Influenza A viruses are found in many animals, and the emergence of influenza A virus, with the ability to infect humans and sustained human-to-human transmission, may lead to an influenza pandemic.
Influenza A viruses are classified into subtypes according to the groups of proteins found on the surface of the virus. When animal influenza viruses infect their host species, they are named according to the host, such as avian influenza viruses that infect birds, and swine influenza viruses that infect pigs. These animal influenza viruses differ from human influenza viruses and are not easily transmitted to or among humans.
Avian influenza virus
The highly virulent avian influenza virus subtype H5N1 (H5N1) is among the viruses of greatest concern.
The H5N1 bird influenza virus first gained attention in 1997 during an outbreak in Hong Kong, and has since caused periodic outbreaks throughout Asia, Africa, and the Middle East. There are other forms of highly virulent bird influenza, including H5N6, H5N8, and H7N9. and H7N7.
According to the US Centers for Disease Control and Prevention, 66 people across the United States have tested positive for H5N1 since the beginning of 2024. There are currently no known cases of human-to-human transmission of the virus, with all cases stemming from exposure to infected animals.
Cells ready for defense
The new study revealed that people who have had the flu or received a flu vaccine in the past may have ready cells – T cells – to defend the body in the event of infection with bird flu.
“We anticipate that there is a degree of prior immunity in the general human population that could mitigate the severity of human H5N1 infection,” the researchers wrote in the paper.
In the paper, the researchers compared the genetic sequences of H5N1 viruses with those of seasonal influenza viruses and found similarities to certain parts of the seasonal influenza genome.
Immune T cells, or T lymphocytes, a type of white blood cell, play a pivotal role in the adaptive immune system, helping to identify and eliminate pathogens. Memory T cells in particular remember previous infections, allowing the immune system to respond faster and more effectively when exposed again to the same pathogen. This is why we are less susceptible to pathogens after we have already been infected, or received a vaccine.
“We can predict that our T cells – in most cases – have responses and can provide prior immunity to the H5N1 virus, and this is good news,” Alba Griffoni, an assistant professor at the La Jolla Institute of Immunology, said in a statement according to Newsweek.
Researchers say that these cross-reactive T cells could help us fight the H5N1 virus if it evolves to spread among humans.