Bird Flu Less Alarming Due to Existing Immunity from Flu Shots

Research into the potential for preexisting immunity against H5N1 avian influenza suggests a complex landscape where seasonal flu exposure may provide minimal protection, though it remains unclear if such immunity can prevent a widespread pandemic.

While some evidence indicates that previous infections or vaccinations against seasonal flu can generate low levels of antibodies that recognize bird flu, other peer-reviewed findings suggest that standard annual flu shots are insufficient to protect the population from the most dangerous strains of H5N1.

Seasonal Vaccines and H5N1 Protection

A study published in Emerging Infectious Diseases by the Francis Crick Institute and University College London Hospitals found that quadrivalent seasonal flu vaccines (QIVs) do not produce protective antibodies against two specific strains of avian influenza A(H5N1).

The research, published June 3, 2025, analyzed blood samples from 61 adults who had received flu vaccines between 2021 and 2024. The researchers tested for responses against a 2023 strain from Cambodia and a 2024 strain detected in U.S. Dairy cattle that had been linked to human infections.

Although the participants showed strong immune responses to the seasonal H1N1 flu virus, none of them demonstrated antibody responses capable of neutralizing the tested H5N1 viruses. This indicates that standard flu shots are unlikely to protect individuals from serious illness if H5N1 begins to spread more widely among humans.

Variations in Preexisting Immunity

Other research suggests that some individuals may possess a small degree of protection. According to a report from Science News published July 29, 2025, some people who have previously caught seasonal flu or received vaccinations have low levels of antibodies against H5N1 avian influenza.

The effectiveness of this immunity appears to depend on the specific strain of seasonal flu encountered. Data indicates that people who were infected with the H1N1 seasonal flu strain had more antibodies aimed at bird flu than those who were infected with the H3N2 strain.

vaccination against H1N1 may boost these antibodies in young children, who typically have fewer antibodies capable of binding to the H5 protein.

However, virologists warn that this protection is limited. Andrew Pekosz, a virologist at the Johns Hopkins Bloomberg School of Public Health, noted that everybody had relatively low levels of antibodies and observed that antibody levels dipped further nine months after infection.

Pekosz further stated that the infection data probably is telling us that any boost in antibodies is going to be short lived.

Potential for Reducing Disease Severity

Despite the lack of full protection, some scientists believe preexisting immunity could still play a role in mitigating the impact of a potential outbreak. Florian Krammer, a virologist at Mount Sinai’s Icahn School of Medicine, discussed the possibility that existing defenses could buffer the most severe consequences of the virus.

That’s very likely not going to protect us as a population from a new pandemic, but it might give us some protection against severe disease.

Florian Krammer, Mount Sinai’s Icahn School of Medicine, March 19, 2025

Rising Risks of Human Transmission

These scientific inquiries come as H5N1 continues to evolve and spread among mammals. The virus has been detected in cats, rodents, and dairy cows, particularly on farms in the United States.

U.S. Officials have identified traces of the virus in wastewater and raw milk. While pasteurized milk is considered safe, the presence of the live virus in unpasteurized products provides an additional route for potential human exposure.

Public health concern centers on the risk that the virus could adapt to spread more easily between people. If H5N1 evolves this capability, researchers emphasize that current seasonal flu vaccines will not be sufficient to protect vulnerable populations, highlighting a critical need for targeted vaccines and improved pandemic preparedness.