Joint Vaccine Against COVID-19 And Flu Provides Strong Protection In Early Tests

We’re all used to the routine by now – we know we need to get a new flu shot every year for the best protection, as well as regular COVID-19 boosters if they’re available. It can be inconvenient, even leaving aside the potential costs depending on your health system and insurance situation.

But it’s also important. There are an estimated 1 billion cases of seasonal influenza across the globe every year, causing up to 650,000 deaths. The current Northern Hemisphere flu season has been hitting headlines, with health authorities in various countries reporting high case numbers.

COVID-19, meanwhile, began to wreak havoc on our world five years ago. While the rapid development of effective vaccines undoubtedly saved many lives and allowed us to move out of the initial emergency phase of the pandemic, the disease and its lasting consequences have not gone away. 

“Although individual vaccines have been developed and approved for use in humans against SARS-CoV-2 and influenza viruses, there is no vaccine approved to simultaneously protect against both viral diseases, which continue to impact public health globally,” reads the new paper.

The team, from Cornell University, therefore set out to develop a bivalent vaccine, containing pieces of both viruses. 

The vaccine candidate they came up with is based on yet another virus – stay with us! – called vesicular stomatitis virus (VSV). The VSV particle they used is what’s called replication-incompetent, meaning it lacks all the machinery it would need to reproduce itself. You can think of it as a vessel to carry the flu and SARS-CoV-2 viral proteins where they need to go. 

Those proteins in this case are the SARS-CoV-2 spike protein, which has always been a key focus of research during this pandemic and is vital to the virus’s ability to invade our cells; and an influenza A cell surface protein called neuraminidase. If you’ve heard of flu viruses described by their “H” and “N” numbers – H5N1 is all over the news right now – the N refers to neuraminidase.

In this way, the approach stands out from current flu vaccines, which generally use haemagglutinin (the “H” number). There are fewer subtypes of neuraminidase, and previous research has suggested that it could be a good candidate for universal flu vaccines, offering broad-spectrum protection. 

After the authors optimized the production of their VSV-based vaccine candidate, they tried it out in mice. After receiving either the real vaccine or a mock vaccine as a control, the mice were carefully monitored for four days before serum samples were obtained. Testing revealed that the vaccine induced a strong antibody response against SARS-CoV-2 and a weaker response against the influenza virus. 

As well as cellular assays to further measure the immune response, vaccinated and control mice were exposed to either SARS-CoV-2 or an H1N1 flu strain. All of the control mice got sick or died, but the vaccinated mice were well protected.

The findings are promising and aren’t necessarily limited to COVID-19 and flu – a VSV-based vaccine already exists in the form of one of only two approved vaccines against Ebola. The authors also discuss their own previous work using a VSV platform to immunize against Ebola, Nipah virus disease, and Hendra virus disease. 

“This study highlights the potential of multivalent vaccine approaches targeting enveloped respiratory viruses with similar transmission patterns, addressing global vaccine demands,” the authors conclude.

The study is published in the journal Science Advances.