Is it a cold or the flu? A common cold, including chest cold and head cold, can be caused by more than 200 viruses. Seasonal flu is caused by three types of viruses: influenza A, B, and C. Flu season usually occurs in the UK from October to April. The NHS provides flu jabs between late September and early November for those people most at risk from developing complications. At-risk patients may also be prescribed antiviral medications like zanamivir (Relenza) or oseltamivir (Tamiflu) soon after flu symptoms start.