Cooler weather heralds the peak influenza season in Hong Kong, and it’s time to book ourselves in for a flu jab. It’s no one’s favourite annual event, but in the future we might be able to acquire lifelong immunity with just a single shot.
Dr Sophie Valkenburg is a post-doctoral research fellow at Hong Kong University’s School of Public Health. She’s part of a team working in collaboration with researchers at the National Institutes of Health in the United States to develop a new type of influenza vaccination which promises to be more effective, and longer lasting, than anything now available.
“The current generation of flu vaccines are good but they have limitations,” says Valkenburg. These limitations include the notorious seasonality. “The current vaccine requires worldwide surveillance from a network of labs, coordinated by the World Health Organisation. They predict which strain to include in the vaccine for the upcoming flu season”.
The key to designing a truly effective vaccine is to tailor it to trigger a response that’s even stronger than our natural response to the actual flu virus, but without making you ill.
When we catch the flu, our immune system detects the infection and mounts a multi-pronged defence. An army of antibodies, tailor-made to attack the particular virus, are produced. The antibodies mostly bind to a virus’s surface, preventing it from entering healthy cells.
The body also produces T cells. There are two main types. Killer T cells hunt down infected cells and destroy them. Helper T cells play a less aggressive but equally important role, orchestrating the work of the other immune cells, boosting the production of antibodies and coordinating the activity of the killer T cells.
“Antibodies are designed to block the viruses but sometimes they fail to stop the virus breaking through, in which case the T cells are there as back up” says Valkenburg. “That’s why it’s important to have all arms of the immune system operating.”
Current vaccines primarily trigger an antibody response which is why we need an update every year.
“Antibodies recognise the outer surface of a virus, and as the virus mutates, and even swaps genetic code with other viruses, the surface continually changes. From one year to the next the outside of the virus might look only 40 per cent the same as last year’s virus,” explains Valkenburg.
The antibodies ‘remember’ the specific virus they were produced to fight, but as the enemy is constantly changing, the immunity they confer doesn’t last.
“It’s like a software update,” says Valkenburg. “The old response soon becomes out of date.”
The vaccine Valkenburg and her team are developing incorporates more influenza proteins than have been used before. Studies on mice have shown that it provokes both a strong antibody response and a broad T cell response – a double whammy for the flu viruses.
Like antibodies, T cells can recognise the outside of the flu virus but, crucially, they recognise the inside too. “The internal proteins have 90-95 per cent conservation between different viruses,” says Valkenburg.
Best of all, the new vaccine triggers a powerful helper T cell response. “This is the key to getting a good antibody response and a good killer T cell response,” says Valkenburg.
Not only will the new vaccine provide stronger, longer-lasting immunity, it will also protect against more influenza strains.
Influenza falls into two broad categories – the relatively familiar ‘seasonal’ flu strains which flare up every winter, and ‘outbreak’ flu. These are the pandemic influenzas, such as swine and avian flu. We lack natural immunity to many of these new viruses which is why mortality rates can be staggeringly high – as much as 60 per cent for some strains.
Current vaccines are only effective against seasonal flu and offer no protection against outbreak strains. The new vaccine, with its added helper T cell response, encompasses outbreak strains too.
“So far it has worked against every virus we’ve thrown at it. It looks very promising” says Valkenburg.