The battle continues against H5N1 flu in North America, but followers of the news will be reassured to hear that a cutting edge H5N1 vaccine for the highly virulent strain currently spreading in cows is in the works. Since seasonal flu vaccines do not protect against H5N1 flu, vaccine scientists have been racing against the virus to generate an effective shot before it starts transmitting between humans.
National Institutes of Health (NIH) Scientists reported last week in Nature Communications that they have successfully developed an effective vaccine against the bird flu virus currently spreading in dairy herds. The researchers demonstrated that immunization with their novel jab provided complete protection in preclinical testing.1
Making an H5N1 Vaccine
The strain of H5N1 flu making the rounds right now has public health officials across North America deeply concerned.2 The US Centres of Disease Control (CDC) has been preparing for an H5N1 outbreak for some years.3 Currently scientists are encouraged to create what they call a Candidate Vaccine Virus (CVV).4 In short, flu researchers make educated guesses about which strains of H5N1 virus might circulate in the next year or so. They base these predictions on a database of genetic sequences found in versions of the H5N1 virus that they have seen before.
Once they choose a good suspect, they piece together a sample virus using their DNA database. These virus designs are usually close enough to the real flu virus that if they use it to make a vaccine, they can limit an H5N1 outbreak. The CDC has built a stockpile of candidate vaccines against older variants of the H5N1 virus. In normal circumstances this would be reassuring, however, Montana based Rocky Mountain University Scientists say that this new, more virulent H5N1 strain is evolving fast.
The virus has jumped from birds to dairy cattle, a process which has led to significant mutation of the virus. As a consequence, those stockpiled vaccines may not be as effective as we would like them to be.
A rapid response
The researchers developed an updated vaccine from a current version of the virus isolated from a US dairy cow. Part of the problem with the Clade 2.3.4.4b strain of H5N1 is that the chunk of virus that vaccines typically use to train our immune system has mutated further from historical strains that the CDC would usually expect to find.
After carefully examining its genetic sequence the Rocky Mountain investigators were able to make a shot that targets the variant of the H5N1virus that is now spreading between cows in US dairy herds.
Testing Times
Three sets of mice were vaccinated in the study:
- a group given the new vaccine and challenged against the Clade 2.3.4.4b H5N1 virus;
- a group given an older version of the H5N1 vaccine and tested against the older virus and the Clade 2.3.4.4b H5N1 virus;
- a control group given a vaccine with the same mechanism but with an irrelevant virus and then exposed to both flu viruses.
Four weeks after vaccination, the mice were euthanized and their immune response to the flu viruses was analysed. Mice inoculated with the new vaccine produced an excellent immune response to the Clade 2.3.4.4b strain of H5N1. The mice displayed good antibody levels that effectively neutralized the virus, and conferred complete protection from a lethal dose of the virus. Overall, the mice did well with the vaccine and had minimal side effects.1
The older version of the H5N1 bird flu vaccine that targeted a strain that was circulating in Hong Kong during the last large outbreak 2004, performed poorly against Clade 2.3.4.4b H5N1. It seems that the genetic sequence of the HA antigen they used to prepare the candidate vaccine virus has mutated more than would be expected, possibly rendering some of the stockpiled CVVs obsolete.1
Essential Research Into H5N1 Vaccines
This report highlights the importance of the CDC in maintaining an up-to-date stockpile of vaccines and the continuing work by flu researchers to collect and characterize new strains of influenza. MNB will continue to monitor developments in vaccines as this epidemic progresses.
References
- Hawman, D.W., Tipih, T., Hodge, E. et al. Clade 2.3.4.4b but not historical clade 1 HA replicating RNA vaccine protects against bovine H5N1 challenge in mice. Nat Commun 16, 655 (2025). https://doi.org/10.1038/s41467-024-55546-7
- CDC. H5 Bird Flu: Current Situation. Avian Influenza (Bird Flu). January 27, 2025. Accessed January 28, 2025. https://www.cdc.gov/bird-flu/situation-summary/index.html
- CDC. Prevention and Antiviral Treatment of Avian Influenza A Viruses in People. Avian Influenza (Bird Flu). November 6, 2024. Accessed January 28, 2025. https://www.cdc.gov/bird-flu/prevention/index.html
- CDC. Making a Candidate Vaccine Virus (CVV) for a HPAI (Bird Flu) Virus. Avian Influenza (Bird Flu). October 2, 2024. Accessed January 28, 2025. https://www.cdc.gov/bird-flu/php/severe-potential/candidate-vaccine-virus.html
The battle continues against H5N1 flu in North America, but followers of the news will be reassured to hear that a cutting edge H5N1 vaccine for the highly virulent strain currently spreading in cows is in the works. Since seasonal flu vaccines do not protect against H5N1 flu, vaccine scientists have been racing against the virus to generate an effective shot before it starts transmitting between humans. National Institutes of Health (NIH) Scientists reported last week in Nature Communications that they have successfully developed an effective vaccine against the bird flu virus currently spreading in dairy herds. The researchers demonstrated that immunization with their novel jab provided complete protection in preclinical testing.1 The strain of H5N1 flu making the rounds right now has public health officials across North America deeply concerned.2 The US Centres of Disease Control (CDC) has been preparing for an H5N1 outbreak for some years.3 Currently scientists are encouraged to create what they call a Candidate Vaccine Virus (CVV).4 In short, flu researchers make educated guesses about which strains of H5N1 virus might circulate in the next year or so. They base these predictions on a database of genetic sequences found in versions of the H5N1 virus that they have seen before. Once they choose a good suspect, they piece together a sample virus using their DNA database. These virus designs are usually close enough to the real flu virus that if they use it to make a vaccine, they can limit an H5N1 outbreak. The CDC has built a stockpile of candidate vaccines against older variants of the H5N1 virus. In normal circumstances this would be reassuring, however, Montana based Rocky Mountain University Scientists say that this new, more virulent H5N1 strain is evolving fast. The virus has jumped from birds to dairy cattle, a process which has led to significant mutation of the virus. As a consequence, those stockpiled vaccines may not be as effective as we would like them to be. The researchers developed an updated vaccine from a current version of the virus isolated from a US dairy cow. Part of the problem with the Clade 2.3.4.4b strain of H5N1 is that the chunk of virus that vaccines typically use to train our immune system has mutated further from historical strains that the CDC would usually expect to find. After carefully examining its genetic sequence the Rocky Mountain investigators were able to make a shot that targets the variant of the H5N1virus that is now spreading between cows in US dairy herds. Three sets of mice were vaccinated in the study: Four weeks after vaccination, the mice were euthanized and their immune response to the flu viruses was analysed. Mice inoculated with the new vaccine produced an excellent immune response to the Clade 2.3.4.4b strain of H5N1. The mice displayed good antibody levels that effectively neutralized the virus, and conferred complete protection from a lethal dose of the virus. Overall, the mice did well with the vaccine and had minimal side effects.1 The older version of the H5N1 bird flu vaccine that targeted a strain that was circulating in Hong Kong during the last large outbreak 2004, performed poorly against Clade 2.3.4.4b H5N1. It seems that the genetic sequence of the HA antigen they used to prepare the candidate vaccine virus has mutated more than would be expected, possibly rendering some of the stockpiled CVVs obsolete.1 This report highlights the importance of the CDC in maintaining an up-to-date stockpile of vaccines and the continuing work by flu researchers to collect and characterize new strains of influenza. MNB will continue to monitor developments in vaccines as this epidemic progresses.
Making an H5N1 Vaccine
A rapid response
Testing Times
Essential Research Into H5N1 Vaccines
References
