Last week, a third human case of infection by the H5N1 virus, also known as “bird flu”virus, was reported in a farm worker in Michigan. This week, Rick Bright, PhD, the former head of the Biomedical Advanced Research and Development Authority, wrote that the state of spread “is at a dangerous inflection point,” as it is currently in cattle in nine states.
Although the first two human cases caused minor symptoms – such as eye irritation or conjunctivitis – the third case included flu-like symptoms, which has some epidemiologists and other health professionals concerned about the spread of the virus and associated disease into and among people.
Below, Fred Krebs, PhD, an associate professor in the department of Microbiology and Immunology and Institute for Molecular Medicine and Infectious Disease in Drexel University’s College of Medicine and an expert in viruses and viral infections, shared whether it’s safe to drink cow’s milk, how to keep farm workers safe, the current state of monitoring and testing, and whether the U.S. is prepared in the event of a bird flu outbreak in humans.
Please talk briefly about your expertise in preventative and immunotherapeutic approaches to combat viral pathogens.
My interest in preventing and treating viral infections began during my PhD training at the Penn State College of Medicine, where we were working on compounds for use in preventing HIV-1 transmission. Our current research projects at Drexel focus on establishing a novel antiviral and immunologic treatment for herpesvirus infections and developing an immunotherapy for people infected with HIV-1. Both projects involve the use of non-thermal plasma, which is at the heart of the expanding field of plasma medicine.
At this point, only three dairy farm workers have been diagnosed with bird flu. That said, seeing H5N1 in the tissue of cattle is unnerving. What’s your level of concern right now that this could mutate and cause a major outbreak in people?
At present, the risk to the general public – those outside the dairy industry – is low. The three dairy workers were apparently infected through close proximity to dairy cattle carrying the virus. In the absence of evidence that the virus is being transmitted from person to person, my level of concern remains low.
It may be beneficial to define some terminology. The terms “avian influenza,” “avian flu,” and “bird flu” describe the disease caused by infection with a specific kind of influenza virus. While the bird flu virus is typically limited to infections of wild aquatic birds and other animals, this type of virus can occasionally infect humans. The term “H5N1” refers to specific variations in two proteins contained within influenza viruses. Variations in these two proteins are used to classify all influenza viruses, including bird flu viruses as well as the strains that arise during the annual flu seasons.
It’s also important to remember when reading about the bird flu virus that the term “Highly Pathogenic Avian Influenza (HPAI)” is not as scary as it sounds. The “highly pathogenic” part of the name refers to the disease severity in birds but not necessarily in humans.
Based on what we know, is pasteurized milk safe to drink? How about unpasteurized milk?
I consider pasteurized milk to be safe to drink. Studies published on May 24 in the New England Journal of Medicine demonstrated that simple heat treatment inactivated over 99.99% of infectious bird flu virus in raw milk from infected cows. Since this laboratory experiment was not designed to replicate the rigorous and controlled conditions of large-scale industrial pasteurization, I think it’s safe to assume that the risk of bird flu infection by drinking pasteurized milk is negligible.
The risk posed by raw (i.e., not pasteurized) milk is a different story. In those same studies, mice fed raw milk from an infected cow were readily infected by the bird flu virus and developed symptoms of infection one day later. Of course, consumption of raw cow’s milk is not advisable for other reasons. Drinking raw milk also puts someone at risk for infection by disease-causing bacteria such as E. coli and several types of Salmonella.
Following concern from public health experts about farmers being resistant to testing workers, wearing protective gear while touching animals, etc., the federal government is now giving farms financial incentive to help combat the spread of H5N1 bird flu. Do you expect this to help?
Prevention, surveillance, reporting, and dissemination of information are all important elements of an effective response to an emerging virus.
First, measures like cattle testing and the use of personal protective equipment (PPE) by dairy workers will help efforts to limit the spread of the virus among animals and prevent infections in people. Limiting the spread of the virus to a variety of wild and domesticated animals will reduce the probability that the virus will mutate into a strain that can pass easily among humans.
Second, testing people for the virus, as well as consistent and timely reporting of human infections, will increase our chances of early detection and containment of a virus that may have mutated into a variant that can be transmitted from person to person. While wastewater surveillance doesn’t provide information about individual infections of animals or humans, it is nevertheless useful for monitoring the spread of the virus within a community. In addition, wastewater surveillance can be used as an early warning system to detect outbreaks of other important human pathogens, such as measles virus, poliovirus, the virus that causes COVID-19, and mpox virus.
Finally, the bird flu website maintained by the Centers for Disease Control and Prevention (CDC) is a valuable source of up-to-date information and guidance. Within an information landscape that includes a considerable number of questionable sources, the CDC website offers timely information and expert guidance to the general public, physicians and healthcare workers, and researchers. The CDC’s H5N1 Bird Flu: Current Situation Summary provides details about findings and events as they become available.
It looks like we have two candidate vaccine viruses that can be used to protect against bird flu and possibly an mRNA-based vaccine. Is there data available yet to suggest how effective the vaccines would be?
The current vaccine picture includes products that are available and products under development. As of February, the World Health Organization reported the availability of four vaccines against a type of virus related to those found in cattle and the three dairy workers. The same report indicated that two more vaccines against that same type of virus are now under development. As stated by the CDC, preliminary data indicate these vaccines “may provide reasonable protection” against the current bird flu virus. It’s also important to note that the current seasonal vaccines are not effective against the bird flu virus.
Given the success of mRNA-based vaccines against the COVID-19 virus, it’s not surprising that efforts are moving ahead to develop a bird flu virus vaccine using this technology. Researchers at the University of Pennsylvania have already shown that an mRNA bird flu vaccine is highly effective in preventing virus-associated disease and death in small animal models. This same vaccine will be tested in cattle next month by the U.S. Department of Agriculture (USDA). Building on their success with an mRNA-based vaccine against the COVID-19 virus, Moderna is reported to be in talks with the U.S. government to test and produce an mRNA vaccine effective in humans against the current bird flu virus.
What’s the likelihood that this virus will mutate and lead to human-to-human transmission?
The emergence of a virus variant that can spread from human to human will depend on the opportunities that the current virus has to spread to and mutate in different animal populations. If the spread of the current bird flu virus can be limited through surveillance and perhaps vaccination of cattle and other domesticated animals, the probability that an epidemic- or pandemic-level virus will emerge will be reduced.
Can we expect to have enough doses available in the event of an outbreak in humans? What are your biggest concerns from a vaccination standpoint?
Answers to your questions combine good news with some concerns. I’ll start with the four pieces of good news. First and as mentioned above, there are existing stocks of bird flu virus vaccines that may provide some protection against the current virus. Second, production and distribution of new bird flu vaccines will be facilitated by decades of experience in manufacturing and distributing seasonal flu vaccines around the world. Third, the U.S. government recently ordered 4.8 million doses of the H5N1 (bird flu) vaccine to prepare for a potential bird flu virus epidemic or pandemic. Fourth, mRNA vaccines, which look promising against the bird flu virus in early animal testing, may again play significant roles in our responses to a global virus outbreak.
There is, however, an important concern relevant to making vaccines available in response to a rapidly expanding epidemic or pandemic. The methods historically used to manufacture vaccines are not conducive to rapid production; manufacturing large quantities of vaccines by traditional approaches can take months. While mRNA vaccine technology has been shown to offer a more agile and rapid response to a critical vaccine need, mRNA vaccines specific to the bird flu virus have not yet been shown to be effective in humans. Trials in humans will need to be conducted before bird flu virus mRNA vaccines can be made available for widespread distribution. However, the promising results from recent animal studies, which mirror early successes achieved with the COVID-19 mRNA vaccine, suggest that mRNA vaccines could be part of early responses to an emerging bird flu virus that is capable of human-to-human transmission.
Media interested in speaking with Krebs should contact Assistant Director of News & Media Relations, Greg Richter, at gdr33@drexel.edu or 215.895.2614.
