Nasal spray could prevent infections from any flu strain

An antibody nasal spray has shown promise for protecting against flu in preliminary human trials, after first being validated in mice and monkeys. It may be useful for combatting future flu pandemics because it seems to neutralise any kind of influenza virus, including ones that spill over from non-human animals.

The main tool we have for stopping the spread of flu is the annual vaccine, which stimulates our immune system to make antibodies against recently circulating strains of influenza virus. However, because influenza strains are constantly morphing, vaccines are only moderately effective.

To address this, pharmaceutical company Johnson & Johnson developed a special antibody called CR9114 that can neutralise any of these strains. It does this by recognising and binding to a part of the virus that always stays the same, regardless of how other parts of it are changing.

When CR9114 was initially injected into animals’ bloodstreams, it failed to provide robust protection against flu. This was because only a small proportion reached the nose, the main point of entry for influenza viruses. In 2022, the firm Leyden Labs licensed CR9114 and developed a formulation that could be sprayed up the nose instead.

Since then, the company has shown that spraying CR9114 up the noses of mice and macaques stops them from getting sick when they are exposed to various strains of influenza A and B, including one collected from a scientist’s throat during a bad flu season in 1933.

Preliminary tests were also conducted in 143 people aged 18 to 55. Researchers found that administering the spray twice a day maintained steady levels of the antibody inside participants’ noses and didn’t cause any major side-effects. Samples of their nasal mucus collected afterwards also neutralised a range of influenza strains, including a bird flu strain that crossed into people in China in 2013.

The next step will be to directly expose people who have used the spray to a range of influenza viruses to confirm that it actually stops them from getting sick.

The spray may not be 100 per cent effective because the virus can enter the body via routes other than the nose, like the mouth, says Linda Wakim at the University of Melbourne, Australia. “But nonetheless, blocking nasal entry would still intercept the virus at a major access point for infection.”

It will probably also be less convenient than the flu vaccine because it requires twice-daily administration rather than a single jab, says Wakim. “However, it could be a game changer for specific high-risk groups, such as immunocompromised individuals, frontline healthcare workers, or during a pandemic situation where rapid, short-term population protection is needed while vaccines are being developed or rolled out.”