Exhibitions prior to specific types of seasonal influenza virus promote cross -reaction immunity against the H5N1 Avian influenza virus, according to a new research from the Perelman School of Medicine of the University of Pennsylvania. It was found that older adults who were exposed to seasonal flu viruses that circulated before 1968 were more likely to have antibodies that bind to the H5N1 avian flu virus. The findings, published today in Nature Medicine¸ Suggest that younger adults and children would benefit more from H5N1 vaccines, even those not specifically adapted to the current strain that circulates in birds and cattle.
“We know that early childhood influenza exhibitions can cause immune responses that last a lifetime,” said Senior Scott Hensley author, PHD, professor of microbiology. “We discovered that antibody responses were prepared by H1N1 and H3N2 viruses decades ago they can react crossed to H5N1 avian viruses that circulate today. Most of these reactive antibodies cannot prevent infections, but they will probably limit the disease if we have an H5N1 film.”
Potential protection of a virus that changes rapidly
The H5N1 viruses have circulated in the birds for many years, but a new version, called CLADE 2.3.4B, the H5N1 virus emerged more recently and since then it has spread among the cattle. This current H5N1 strain does not bind receptors on the Human upper airway, but generalized circulation in mammals could lead to mutations that help the virus to infect the cells of the human respiratory tract and increase the transmission. If this happens, H5N1 could begin to extend from human to human.
The influenza viruses are covered with two lollipop -shaped proteins called hemaglutinine and neuraminidase, for which viruses are named (H5N1, for example). These proteins are what allows a virus to bind to “healthy” cells and begin the infection process. Current influenza vaccines mainly cause antibodies that recognize hemaglutinine proteins and prevent a person from infected with a person. The “heads” of the hemaglutinine proteins evolve more frequently, while the “sticks” of hemaglutinine lollipops, called stems, do not evolve so fast.
The researchers tested blood samples of more than 150 people born between 1927 and 2016 for antibodies aimed at stem proteins of different influenza viruses, including H5N1. They discovered that the blood samples of older adults born before 1968 that were probably first exposed to H1N1 or H2N2 in childhood had higher levels of antibodies that could join the stem of the H5N1 virus. They discovered that the year of an individual was closely related to the amount of antibodies to combat H5N1 in their blood. Young children who were not exposed to seasonal flu viruses had low levels of antibodies that could fight H5N1.
Existing vaccines are effective
To determine how individuals with different years of birth respond to H5N1 vaccines, the researchers obtained blood samples from a separate group of individuals born between 1918 and 2003 before and after they were vaccinated with an H5N1 2004 vaccine that did not coincide perfectly with the clade 2.3.4B H5N1 virus that is currently circulating.
According to the initial findings of researchers, older adults had greater amounts of antibodies that could join H5 stems before vaccination. After vaccination, H5 stem antibodies increased slightly in older adults, but increased substantially in children. These antibodies bind both to the H5N1 2004 virus and clado 2.3.4.4b of the H5N1 virus that circulates today.
“In the case of an H5N1 pandemic, all age groups will probably be highly susceptible, but it is possible that the highest disease load is in children,” said Hensley. “If this is the case, children must be prioritized for H5N1 vaccines.”
This research was supported by the National Institute of Allergies and Infectious Diseases (75N93021C00015, R01AI08686).