Sanofi said it has temporarily suspended the supply and sales of two types of seasonal flu vaccines in China as a precautionary measure due to decline in potency.

It expects the efficacy could possibly be affected before the product shelf life for one of the antigens in the vaccines and thus had taken the precaution of suspending the sales.

Potency is defined as the measure of a vaccine’s biological activity, and is directly linked to its effectiveness.

The company said it had found the potency decline during a routine quality follow-up testing in one of its sites in China for products that had not yet been distributed for the 2024-2025 influenza season.

All the trivalent Vaxigrip and the quadrivalent VaxigripTetra seasonal flu vaccines that were already distributed meet the necessary specifications for release and are both safe and effective, and there’s no indication safety and efficacy of these vaccines have been affected.

The suspension of sales of Sanofi products won’t influence the city’s flu shots, the local disease control and prevention authority said.

Flu vaccinations are not mandatory, with injections based on demand and people paying for them themselves.

Apart from Sanofi, there are another 10 plants offering flu vaccinations in Shanghai.

Officials from Shanghai United Family Hospital said flu vaccines from Sinovac and Adimmune had arrived at the hospital and people can make appointments. Supply is sufficient, officials said.

SinoUnited Health also said flu vaccines had arrived and people can make appointments via its WeChat mini program.

Flu is seasonal and a flu vaccination each year is recommended for better protection.

The best time to receive the injection is before late October, as the peak season for flu in China is winter and spring and usually starts in November.

Children can receive flu shots from six months. Children from six to 35 months should receive two injections with an interval of at least four weeks. Those aged three years or older can receive a one-dose injection.

In addition to flu shots, good personal hygiene, good sleep, a balanced diet and proper exercise are said to be important for flu prevention and control.