World’s first RSV vaccine could be approved in 2023

The respiratory syncytial virus, better known as RSV, is a major killer for the very young and very old, but we are almost certainly at a turning point in the battle to prevent its lethality.

On Jan. 17, Moderna reported encouraging results from trials of a vaccine in older people, the latest of four such trials conducted by various pharmaceutical companies that have reported very encouraging results. This could mean that 2023 is the year the first RSV vaccine is approved anywhere in the world.

What’s more, long-term antibody treatment was approved in 2022 in the European Union and the UK to prevent healthy children from becoming infected with RSV. If these preventive measures live up to their promise, they could together save tens of thousands of lives.

RSV infects all of us throughout life. In most people, it causes cold symptoms, but among the more vulnerable, such as infants and the elderly, it can be fatal.

Around 100,000 children, most of them very young, die from RSV worldwide each year, says Harish Nair of the University of Edinburgh, UK. Of these deaths, 97 percent occur in low- or middle-income countries, he said.

When it comes to mortality among the elderly, we don’t know the exact numbers, says Nair. In high-income countries, at least 15,000 adult deaths from RSV occur each year, with the risk increasing with age. However, since most people are not tested for the virus, the real figure is probably two or three times higher, he says. There are no statistics on mortality from RSV among older people in low- and middle-income countries.

For every RSV death, many more people become seriously ill, with millions requiring hospitalization.

Developing RSV vaccines has historically been challenging because the main protein on the outside of the virus, called the F protein, changes shape when cells are infected. The most effective antibodies, whether natural or manufactured, target the portion of this protein that is only exposed prior to this shape change.

In 2013, researchers at the U.S. National Institutes of Health introduced a synthetic form of the F protein that is locked into a pre-infectious form. Companies including GSK, Pfizer and Moderna have developed vaccines based on this closed-open protein.

The GSK and Pfizer vaccines are made from the protein itself, while the Moderna vaccine contains an mRNA coding sequence that allows cells to make the protein after injection.

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

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

We do not yet know how effective any RSV vaccine will be in young children, as trials are still in their early stages. But in November 2022, Pfizer reported that when its vaccine was given during pregnancy, it was about 80% effective in preventing severe infections in babies up to 90 days after they were born, and then that protection gradually wore off.

The initial protection results from babies receiving antibodies through the placenta, which then circulate in their blood.

Similar protection can be provided by injecting factory-produced antibodies. In 2022, the EU and UK approved an antibody called nirsevimab (Beifortus) after studies showed that a single injection before RSV season protected children from severe infections. The antibody is being evaluated for US approval.

Nirsevimab is not the first antibody to prevent RSV infection, but it persists in the body much longer, allowing it to be given to healthy children as a preventive measure. However, its manufacturer AstraZeneca has not yet announced the cost of the antibody, Nair says. Factory antibodies are usually very expensive.

But as Pfizer’s vaccine is expected to be approved in many countries for use in pregnancy, two options for preventing RSV infections in children may soon be available in some countries: an antibody and a vaccine given during pregnancy. Given that half of all RSV deaths in children occur in children under six months of age, this could significantly reduce infant mortality.

Thus, there are many reasons to be optimistic that we will see a huge reduction in mortality and medical complications caused by RSV.

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