During the week No 51 (20.12.2021 - 26.12.2021) ARI and influenza intensity in Bulgaria increase compared to the previous 50 (13.12.2021 - 19.12.2021). The total incidence per 10,000 population was 72.95 (during week No 50 the incidence was 85.86). From a total of 345 591 persons under surveillance, belonging to all age groups, a total of  2 521 ARI cases have been reported (during week No 50 the cases were 3 379). The incidence was highest in the age group 0-4 yrs (314.68 per 10,000 population), followed by age group of 5-14 yrs (215.21 per 10,000 population).