Last updated on February 22nd, 2025 at 10:59 am

The H5N1 avian influenza variant, popularly called “bird flu,” has recently become a topic of conversation. People wonder if it might become a pandemic if vaccines work, or if it’s nothing.

We don’t know much right now because it’s very early, with just a handful of cases in the USA, mainly in California. Of course, for those of us who watched the COVID pandemic start with a flicker, we are all wondering if it’s deja vu.

This post will answer a few questions about H5N1 bird flu, but I want to state a gigantic caveat — everything I state will probably change in a few weeks or months.

What is H5N1 bird flu?

Avian influenza, or what everyone is now calling “bird flu,” is a type A influenza subtype designated as A(H5N1). The designation is based on antigens common to this influenza subtype.

Avian influenza viruses are classified into subtypes, which are named according to subtle variations in the structure of two key proteins on the virus surface — hemagglutinin (H) and neuraminidase (N). The hemagglutinin protein is what allows the virus to attach to the cell surface of the host, and then infect the cells. In general, H1 and H3 are best able to attach to human cells, while H5 is best at attaching to bird cells. However, H5 could mutate to a form that makes it better at attaching to human cells, and that would lead to human-to-human transmission of the disease.

Another avian influenza is designated as A(H5N9), but the current bird flu outbreak appears to be the H5N1 subtype. Thus, H5N9 and H5N1 have the same hemagglutinin protein, but a different neuraminidase protein.

As the name implies, these viruses usually affect birds but can occasionally pass from birds to humans, cattle, pigs, and other animals. The H5N1 subtype arose in Asia a few years ago and has spread worldwide. It is highly pathogenic (meaning it can cause disease in humans) and has passed to humans several times.

Infected birds shed the virus through their saliva, mucous, and feces. Human infections with bird flu viruses can happen when the virus gets into a person’s eyes, nose, or mouth, or is inhaled. This can happen when the virus is in the air (in droplets or possibly dust) and a person breathes it in, or possibly when a person touches something that has the virus on it and then touches their mouth, eyes, or nose. Human infections with bird flu viruses have occurred most often after unprotected contact with infected birds or surfaces contaminated with bird flu viruses. However, some infections have been identified where direct contact with infected birds or their environment was unknown.

There are numerous cases where bird flu has been transmitted between humans, but most infections of humans are from constant contact with infected birds. Human infection with avian influenza A virus poses pandemic potential, so CDC and other public health agencies investigate every case to assess whether human-to-human transmission might have occurred. Detailed public health investigations can help determine whether person-to-person spread of an avian influenza A virus occurred.

The signs and symptoms of bird flu infections in humans can range from nothing to severe. The infections are similar to other flu infections including fever, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue, and shortness of breath.

According to data collected by the WHO, there have been 954 documented cases between 2003 and 2024. Of those, 464 were fatal, leading to a fatality rate of about 49 percent among the documented cases.

What is the current state of the outbreak?

As of 8 January 2025, the CDC reports that there have been 66 cases of H5N1 in humans in 10 states. Most of the cases were from contact with cattle and poultry. There has not been any incidence of human-to-human infection.

H5N1 has been found widely in wild birds, poultry, and cattle.

As of today, there has been one death, in Louisiana, from H5N1. The person who was infected was over the age of 65 and had underlying medical conditions, which made the person particularly vulnerable to severe disease. This individual appeared to have contracted the virus from wild birds.

A 13-year-old girl in Canada also developed severe disease from an H5N1 infection in November and required intensive care, intubation, and the use of the life-support therapy extracorporeal membrane oxygenation (ECMO). The child is recovering. The virus isolated from the child showed some worrying mutations that could mean that H5N1 may be better adapted to infecting humans.

As of today, the disease seems to be most prevalent in the US, Canada, and Southeast Asia.

As I mentioned above, there has been no known human-to-human infection. However, and this is something that seems to be ignored, H5N1 has infected large numbers of cattle and poultry. These reservoirs for the disease can increase the risk of a mutation that suddenly makes the virus more infectious — suddenly, we’re in a pandemic again.

I am troubled that various agencies have not invested more effort into reducing the outbreaks in cattle and poultry, because they are reservoirs for H5N1 bird flu.

Is there a vaccine?

As I have previously written, there are no available vaccines for the H5N1 virus. The CDC maintains a small stock of a candidate vaccine for H5N1, but it has not been tested against the current virus, so we do not know its effectiveness. These doses will be used to vaccinate frontline workers if this outbreak grows.

The new universal flu vaccine may be more effective against H5N1 because it targets immunity against more conserved regions of the influenza A virus. However, it has to be tested against the variant, so we cannot be sure it will work.

On the other hand, the current seasonal flu vaccine probably does not protect against H5N1 since it targets other variants of the flu. It might slightly increase your immunity to H5N1 since the targeted influenza A variants in the vaccine share some similarities to H5N1.

As of today, the CDC is monitoring the situation closely so that they can respond quickly, if necessary, with a new vaccine.

Is there a chance that H5N1 bird flu becomes a pandemic?

Your Local Epidemiologist recently wrote:

The probability of a pandemic in any given year is 2%. Spillovers happen all the time, but very few become pandemics because many unlucky things must occur in sequence. The situation unfolding with H5N1 has increased the probability. CDC placed the potential risk of H5N1 to humans as “moderate,” and Metaculus (who hosts a CDC-sponsored respiratory disease forecasting tournament) places the probability of a pandemic in the next year at 5%. In May 2024, I wagered 5%. I now think it’s 7-9% given that H5N1 continues to spread largely unchecked.

So the chances are small, but according to the experts, the chances are growing. And given that this is the heart of the flu season, this could mean that the disease could spread quickly in the Northern Hemisphere.

I vary from grave concern to slight concern depending on what I’m reading at the time. I am extremely worried that the new team of vaccine-denying crackpots who will be running our public health effort will mess this up like they did with COVID. That is cause for grave concern.

How to prevent H5N1?

First of all, do not drink raw milk. It has zero health benefits (NONE) and it is a great way to contract bird flu from cattle. Pasteurized milk kills viruses and does not change the health benefits of milk. This should not be a discussion point, but here we are.

Here are a few other recommendations:

• Avoid contact with wild birds. Do not touch a dead or sickly bird, contact your public health agency in your area to collect it.
• Wear personal protective equipment when you are around sick animals.
• Get the seasonal flu vaccine. It may not protect you against H5N1, but it will reduce your risk of coinfection with the seasonal flu and the bird flu.
• If H5N1 does cause human-to-human infection, pull out that N95 face mask that’s been hanging on your car mirror and wear it.

Can pets get H5N1?

Absolutely yes. Cats on farms contract H5N1 by drinking raw milk, eating raw food, or coming into contact with wild birds or poultry that are sick with the disease. About 50% of cats die from H5N1 (and are another reservoir for mutations that can make the virus more infectious).

Citations

• Jassem AN, Roberts A, Tyson J, Zlosnik JEA, Russell SL, Caleta JM, Eckbo EJ, Gao R, Chestley T, Grant J, Uyeki TM, Prystajecky NA, Himsworth CG, MacBain E, Ranadheera C, Li L, Hoang LMN, Bastien N, Goldfarb DM. Critical Illness in an Adolescent with Influenza A(H5N1) Virus Infection. N Engl J Med. 2024 Dec 31. doi: 10.1056/NEJMc2415890. Epub ahead of print. PMID: 39740022.