The first ever vaccine against RSV could be approved in 2023

By Michael Le Page

The respiratory syncytial virus, better known as RSV, is a major killer of very young and very old people, but we are almost certainly at a turning point in the battle to prevent it being so lethal.

On 17 January, Moderna reported promising results from a vaccine trial in older adults, the latest of four such trials by various pharmaceutical companies to announce highly encouraging outcomes. This may mean that 2023 is the year that the first RSV vaccine is approved anywhere in the world.

What’s more, a long-lasting antibody treatment that prevents otherwise healthy babies from catching RSV was approved in the European Union and UK in 2022. If these preventative measures live up to their promise, they could together save tens of thousands of lives.

RSV infects us all during our life. In most people, it causes cold-like symptoms, but among the more vulnerable, such as babies and older people, it can be deadly.

Around 100,000 children, most of whom are very young, die from RSV every year worldwide, says Harish Nair at the University of Edinburgh, UK. Of these deaths, 97 per cent occur in low or middle-income countries, he says.

When it comes to deaths in older people, we don’t know the exact numbers, says Nair. High-income countries report at least 15,000 adult RSV deaths a year, with the risk increasing with old age. As most people aren’t tested for the virus, however, the true figure is probably two or three times higher, he says. Statistics aren’t available for RSV deaths among older people in low and middle-income countries.

For every death from RSV, many more people become seriously ill, with millions needing hospitalisation.

Developing RSV vaccines has historically been difficult because the main protein on the outside of the virus, called the F protein, changes shape when it infects cells. The most effective antibodies, either natural or factory-made, target a part of this protein that is only exposed before this shape change.

In 2013, researchers at the US National Institutes of Health unveiled a synthetic form of the F protein that is locked in the pre-infection shape. Companies including GSK, Pfizer and Moderna have developed vaccines based on this locked-open protein.

The GSK and Pfizer vaccines consist of the protein itself, while the Moderna vaccine contains an mRNA sequence that codes for it, which enables cells to make the protein following the injection.

In trials in people aged 60 and over, each vaccine was more than 80 per cent effective at preventing symptomatic infections.

This suggests that routinely offering one of these RSV vaccines to people aged 60 or over could save many lives, but Nair expects this roll-out to happen only in high-income countries, as a lack of testing means some lower-income countries are less aware of RSV’s toll and the need for a vaccine.

We don’t yet know how effective any RSV vaccine will be among young children, as the trials are still in early stages. But in November 2022, Pfizer reported that when its vaccine was given during pregnancy, it was around 80 per cent effective at preventing severe infections in infants for up to 90 days after their birth, with this protection then gradually fading.

The initial protection is a result of the babies acquiring antibodies via the placenta, which then circulate in their blood.

Similar protection can be provided by injecting factory-made antibodies. In 2022, the EU and UK approved an antibody called nirsevimab (Beyfortus) after studies showed that receiving a single injection ahead of the RSV season protected against severe infections in babies. The antibody is being assessed for approval in the US.

Nirsevimab isn’t the first antibody for preventing RSV infection, but it persists for much longer in the body, making it feasible to administer to otherwise healthy babies as a preventative measure. However, its manufacturer AstraZeneca hasn’t yet announced the cost of the antibody, says Nair. Factory-made antibodies tend to be very expensive.

But, with the Pfizer vaccine expected to be approved in many countries for use in pregnancy, some nations could soon have two options for preventing RSV infections in babies: the antibody and the vaccine given during pregnancy. Given half of all RSV deaths in children are in babies aged less than six months, this could substantially reduce infant fatalities.

So, there are many reasons to be optimistic that we will see a huge fall in the deaths and medical complications caused by RSV.

“New products are coming,” says Nair. “New technologies are coming. It looks very, very promising.”