The postal strike will not prevent GPs ensuring that at-risk patients are vaccinated against swine flu, the Royal College of GPs has pledged.
Appointment letters will be sent out to 14 million people who are priority cases to invite them for vaccination by their family doctors.
However, with three 24-hour Royal Mail strikes starting on Thursday, and more threatened for the months to come, doctors have said they are willing to telephone individually to inform patients of appointments.
Delivery of vaccine supplies began this week, with health professionals told to concentrate on vulnerable groups including diabetics, pregnant women and people with heart disease or damaged immune systems.
Chief medical officer Sir Liam Donaldson had warned that a postal strike would cause problems for the immunisation programme, and president of the Royal College of GPs, Professor Steve Field, described the timing as "unhelpful".
But he added: "There may be some delays in people getting the vaccine, but GPs and patients are pretty resilient and we will find a way."