There are no flu vaccines in Bulgaria yet. In a letter to the health ministry on 29 September, the manufacturers said the World Health Organization chose the strain late, which delayed production.

Pharmacies should get vaccines around the middle of November. Doses for the state programme are expected at the end of the month. The manufacturer guarantees 70,000 doses and is trying to get more.

The delay comes just as the flu season starts. The first flu cases have already been officially recorded, including one at the hospital where Prof Gergana Petrova works.

Other countries also have production problems, not just Bulgaria, said the distributors of the two injectable vaccines. The maker, Viatris, said the problems affect supplies in a number of countries. The company said the situation differs from country to country, and delivery dates and stocks depend on supply planning, regulatory rules and demand on the local market.

Katya Ivkova of the health ministry said the ministry learned about the delayed strain from the letter. She said it cannot act while the distributors themselves are unable to deliver. There is no answer yet on how the doses were shared out, or whether Bulgaria was late with its orders.

Prof Petrova says there is still time to vaccinate, and doctors expect the vaccines to arrive on time. The situation is making parents anxious. A mother of chronically ill children from her programme called her because she is not sure there will be vaccines for them. She plans to travel to a neighbouring country.

Relatives of a child at risk protect the child by getting vaccinated themselves. One mother's child has an immune deficiency and cannot be vaccinated, so everyone around the child gets the shot. This year they are struggling to find vaccines and are ready to travel abroad. The mother believes the vaccine works, which is why the family looks for it every year.

Prof Petrova added that some parents do not care. She said some children have had flu complications three years in a row, and their mother says the doctors will cure them.

Last year, all three main strains of the virus picked up mutations. Prof Iva Hristova said they do not mean a more severe course, a change in the clinical picture or a worse illness.

Experts expect the season to be no harder than usual. They advise people to wear masks that cover the nose and mouth in places where people with flu may be, such as outpatient clinics.