Another Pandemic on the Horizon?

Emerging viruses are nothing new. Scientists have tracked viruses, planned for their potential transmission to and between humans, and developed vaccines and other treatments for centuries – even as early as the 1700s with the smallpox virus and the first known vaccine developed by Edward Jenner.

That said, simply reading the headline “another pandemic” is likely enough to elicit a stress response in most of us (sorry). The world has been through a great deal since early 2020, and no one wants to experience a similar situation again anytime soon. However, most infectious diseases specialists will tell you that the next pandemic is not an “if” but rather a “when.” Viral spread of pandemic proportions is always possible, especially given the ease and speed at which humans can travel around the world. Indeed, our ability to contain transmissible viruses is increasingly difficult – hence the expected alarm when scientists start monitoring a virus more closely for potential zoonotic spillover.

H5N1 rises

The latest virus ringing alarm bells is a subtype of the influenza A virus – H5N1 or bird flu. This isn’t the first time we’re paying close attention to bird flu; there have been many recorded incidents of mass avian flu infection in bird populations over the past few centuries. Various strains of influenza A virus have been documented by scientists, but transmission primarily remained isolated to avian populations. However, in the late 1990s, an outbreak of H5N1 in Hong Kong was detected with zoonotic transmission – causing 18 human infections and six deaths. Although the current trending news on H5N1 bird flu is alarming, I believe it should not be a cause for panic just yet – at least in the US.

There are many factors that enable the easy transmission of influenza A viruses – in this case, H5N1. Scientists have long believed that wild bird populations could be considered the original host of influenza A and bird flu viruses. Over time, as wild bird migratory patterns shifted and the human population and global trade practices increased, we have witnessed increased transmission of such viruses in wild and domestic animals – and in humans.

H5N1 – a strain said to be the most contagious among birds – has been spreading through bird populations since 2020 and is now causing concern due to cases of bird–mammal transmission. Housing large numbers of birds in confined spaces is a major contributor to the increasing spread among birds – as is housing different animal species in one location. Upon infection, it is almost impossible to contain the spread among birds and other animals, which creates the perfect breeding ground for viral mutations.

Of the several stories of H5N1 mammal infections that have recently emerged, a mink farm in Spain dealt with a large outbreak in 2022, which resulted in the loss of thousands of minks and birds across the farm (1). A concerning factor here was the discovery of an uncommon mutation in the PB2 gene in H5N1, which has only been noted once before during the 2009 H1N1 swine flu pandemic. Scientists believe this mutation may possess characteristics that would allow it to be recognized by receptor cells in the human airway.

Drawing on experience

The good news? Even with this genetic mutation identified, the mink farm’s eleven workers who had direct contact with the infected animals remained asymptomatic and tested negative for the virus throughout the incident. Scientists have yet to detect any additional mutations that would increase the virus’ transmissibility to humans, but they are remaining extremely vigilant in monitoring the strain’s spread among bird and animal populations. There have been few documented human infections with the current strain of H5N1 and only one in the US to date.

If we gained anything from the COVID-19 pandemic, it was the ability to quickly implement procedures and plans for containing viruses. We know the spread of bird flu to humans is still extremely rare and that it is transmitted through respiratory droplets, much like COVID-19. However, in an H5N1 infection, the associated droplets are less likely to establish in the upper respiratory tract than those of a COVID-19 infection. Attachment to host cells further down in the respiratory tract makes it much more difficult for droplets to become airborne and infect others (2). However, we learned from the COVID-19 pandemic that strict mask wearing can be effective in minimizing the spread of viral respiratory illnesses; therefore, rapid implementation of precautionary masking could once again prove beneficial should it be needed for an H5N1 breakout among humans.

If a human is infected with H5N1, the incubation period is estimated to be about seven days. Illness severity can range from asymptomatic to acute, with symptoms including a fever, cough, sore throat, body aches, headaches, and fatigue. In severe cases, where the virus settles into the lower respiratory tract, some humans may experience difficulty breathing and go on to develop pneumonia – which can even result in death.

Vaccines and good hygiene practices are some of the most effective tools against contagious diseases; the public should continue to practice good hygiene – encouraging hand washing, wearing a mask in certain settings, and staying home when ill to avoid contact with others. Modern scientific practices allow us to rapidly create safe and effective vaccines to target various viral strains. As with the COVID-19 pandemic, vaccines will be necessary to contain viral spread. Vaccines against avian flu viruses do exist for humans, and manufacturers can tailor a vaccine to a particular strain should it become necessary. The World Health Organization and Centers for Disease Control and Prevention continuously monitor all viruses for mutations and remain at the ready for updating vaccines appropriately. Currently, the US federal government maintains a stockpile of Avian H5N1 vaccines, which could be deployed (3); however, if the strain is different from the stockpiled vaccines, it would be possible to develop and implement a specific H5N1 vaccine in a timely manner – leveraging the lessons learned from rapid vaccine development and dissemination during COVID-19.

As an infection control and prevention specialist, I will be monitoring H5N1 closely and paying attention to reports of mutations that may increase transmissibility to humans. Currently, the risk to humans is still low, but there is enough evidence to suggest we should remain cautiously vigilant at this time. I’m confident that we as scientists, healthcare providers, and humans learned a great deal from the COVID-19 pandemic – and we will be prepared to implement all of these lessons when the next pandemic arises.