Nikolova Z, Kotseva R
Zh Mikrobiol Epidemiol Immunobiol. 1992(11-12):30-2.
The National Influenza Center of Bulgaria made the epidemiological analysis of the spread of influenza virus, type A, for the period of 11 years on the basis of mass laboratory investigations. Subtype A (H1N1) was found to be the main factor of epidemics in 1978 and 1982, while the epidemics of 1980, 1983, 1985, 1986, 1987 and 1988 were mainly caused by subtype A (H3N2). The data of laboratory and epidemiological studies indicated that after 20-year absence influenza virus A, subtype A (H1N1), was found again to circulate among the population of Bulgaria, and in 1978-1988 circulated simultaneously with the previous subtype A (H3N2). The simultaneous circulation of two subtypes of influenza virus was of great importance for the frequency, spread and duration of influenza epidemics.
保加利亚国家流感中心基于大规模实验室调查，对甲型流感病毒传播情况进行了为期11年的流行病学分析。发现甲型（H1N1）亚型是1978年和1982年流感流行的主要因素，而1980年、1983年、1985年、1986年、1987年和1988年的流感流行主要由甲型（H3N2）亚型引起。实验室和流行病学研究数据表明，在甲型流感病毒消失20年后，甲型（H1N1）亚型再次在保加利亚人群中传播，并在1978 - 1988年期间与之前的甲型（H3N2）亚型同时传播。两种流感病毒亚型的同时传播对流感流行的频率、传播范围和持续时间具有重要意义。
