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Influenza activity and influenza viruses
during the 2005-2006 epidemic season in Finland

Updated on May 22, 2006

Influenza A: The first laboratory-confirmed case of infection with influenza A was a 1-year-old boy from the south-east part of Finland; H3 subtype virus antigenically related to A/California/7/2004 and A/New York/55/2004 was isolated from a specimen collected during week 1, 2006. Similarity to A/HongKong/4443/05 and A/Annecy/1138/05 was shown at the National Institute for Medical Research, London. Local outbreaks due to the H3 subtype virus were recorded during weeks 8 to 9 in three garrisons in North and South-East Finland and during weeks 10 to 11 in three garrisons more, one of these in the southern coastal district. During weeks 13 to 14, small local outbreaks and sporadic cases of A/H3 were still recorded in some garrisons in different parts of the country. In the civilian population, sporadic cases and small local outbreaks due to influenza A (a representative proportion of the cases verified as A/H3) were recorded in different parts of Finland from January to the late April. First evidence of circulation of A/H1 was obtained during week 12 in a municipality adjacent to Helsinki; the isolate was antigenically closely related to A/New Caledonia/20/99. During weeks 15 to 16, local outbreaks due to A/H1 were recorded in the civilian population in two localities, one in the south-western part and the other in the northern part of Finland. Afterwards only sporadic influenza A cases were detected.

Influenza B: First evidence of influenza B was obtained in week 4. A local outbreak was recorded in a garrison in Central Finland during week 7 and three additional outbreaks in garrisons in East Finland during weeks 8-9. More outbreaks dotted around Finland began in three garrisons during weeks 11 to 12 and in two garrisons during weeks 13 to 14. In one of the garrisons, infections with influenza B were confirmed virologically during a period of four weeks. In the civilian population, sporadic cases and small local outbreaks were recorded in different parts of Finland from February to the end of April. With exception of one strain that fell to the B/Yamagata/16/88 lineage, the isolates belonged to the B/Victoria/2/87 lineage and, consequently, were separated from B/Jiangsu/10/2003, the influenza B virus component recommended for the 2005-2006 influenza vaccine. Analysis of vaccination-induced antibody response in relation to the current antigenic diversity is in progress. The HA1 sequences from the first nine influenza B virus isolates from Finland fell into two groups, A and B respectively, that differed from each other by four amino acid changes, K48E, E80R, K129N and S217A, and from B/Shangdong/7/97, the influenza B virus component in the vaccine composition for autumn 2003, not more than in 4 to 5 residues ( Table 3 ).

For weekly figures of laboratory-detected influenza viruses, see Table 1 and Table 2.

Table 1: Diagnostic laboratory findings of influenza made by NPHI

(data by week of sampling specimens)

INFLUENZA ISOLATES AND DETECTION OF VIRAL ANTIGENS AND RNA
YEAR	WEEK	A*	A H3	A H1	B	YEAR	WEEK	A*	A H3	A H1	B
2005	35-52	0	0	0	0	2006	1	0	1	0	0
	Total	0	0	0	0		2	0	0	0	0
							3	1	0	0	0
							4	2	1	0	0
							5-6	0	0	0	0
							7	0	1	0	7
							8	0	3	0	7
							9	1	11	0	23
							10	1	10	0	1
							11	3	9	0	7
							12	1	2	1	18
							13	1	6	0	5
							14	2	7	0	9
							15	2	3	5	7
							16	3	1	2	2
							17	0	0	0	0
							18	1	3	0	0
							19**	0	1	0	0
							Total	18	59	8	86

* Not studied for the subtype, ** Incomplete data

Table 2: Diagnostic laboratory findings of influenza made by virological laboratories in association with universities of Helsinki, Kuopio, Oulu and Turku

(data by week of report)

INFLUENZA ISOLATES AND DETECTION OF VIRAL ANTIGENS AND RNA
YEAR	WEEK	A*	A H3	A H1	B	YEAR	WEEK	A*	A H3	A H1	B
2005	35-52	0	0	0	0	2006	1	0	0	0	0
	Total	0	0	0	0		2	0	0	0	0
							3	0	0	0	0
							4	1	0	0	2
							5	3	0	0	1
							6	2	0	0	0
							7	0	0	0	0
							8	4	0	0	2
							9	1	0	0	3
							10	7	0	0	4
							11	13	0	0	6
							12	9	0	0	4
							13	19	0	0	11
							14	8	0	0	6
							15	18	0	0	7
							16	10	0	0	2
							17	4	0	0	6
							18	3	0	0	0
							19	4	0	0	0
							20	1	0	0	1
							Total	107	0	0	55

* Not studied for the subtype, ** Incomplete data

Table 3: Amino acid sequence differences in the HA1 protein between the recent influenza B virus isolates.

	Amino acid residue
	48	80	120	129	199	217
B/Shangdong/7/97	K	K	I	K	N	A
Consensus in Finland in 2002/03	K	K	T	K	T	A
Group A in Finland, 2005/06	K	E	T	K	T	S
Group B in Finland, 2005/06	E	R	T	N	T	A

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