Could vaccines make bird flu worse?

Anti-vaxxers are seizing on an interview Sean Hannity conducted with HHS Secretary Robert Kennedy Jr. to say that bird flu vaccines may not work well and could make the virus stronger, cause more chickens to get sick, and increase egg prices.

These claims show a basic misunderstanding about vaccines and viruses. The idea of a “leaky vaccine” does exist. But as proof, they point to Marek’s disease in chickens. In that case, the virus changed, causing a stronger version that could make unvaccinated chickens sicker. But this has only happened with Marek’s disease, not with other diseases. Even with this “leaky vaccine,” vaccination greatly reduced how much the disease spread and how many chickens got sick. Because of vaccines, chicken deaths from Marek’s disease dropped by 99% from 1970 to 2006.

Another incorrect claim is that vaccines turn birds into mutation factories. Viruses naturally change or mutate over time. But most mutations happen when a lot of sick animals spread the virus. Vaccines actually slow down virus spread, making it harder—not easier—for new mutations to form.

He also claims that chickens would gain natural immunity if they were allowed to catch bird flu. The problem with this idea is that flu viruses mutate very quickly. Also, immunity against one type of flu virus doesn’t always protect against other types.

Scientists around the world agree that vaccinating poultry safely prevents bird flu outbreaks. It also protects farms and reduces the chance that bird flu might spread from birds to people. Vaccines are a safe and effective way to control disease, protect animals, and keep food supplies stable.