Table 4.

Mixed effects linear regression of individual HAIT titre in pigs' sera (≥40 threshold)

HAIT titre in the individual pig
Predictors	Coefficients	SE	P values	95% CI
Antigen subtypes
swH3N2	Reference
swH1N1	188.31	221.34	0.395	−245.51	622.13
swH1N2	−285.43	223.13	0.201	−722.76	151.91
H1N1pdm09	811.53	221.71	<0.001	376.99	1246.07
Year
2009	Reference
2010	−149.38	90.24	0.098	−326.26	27.49
2011	81.26	88.53	0.359	−92.25	254.78
2012	132.23	88.30	0.134	−40.84	305.31
2013	−47.89	88.42	0.588	−221.19	125.41
2014	−63.55	88.85	0.474	−237.69	110.58
2015	−77.27	89.03	0.385	−251.77	97.24
2016	−40.84	89.17	0.647	−215.61	133.93
2017	8.30	91.17	0.927	−170.38	186.99
Production
Fattening	Reference
Sow	100.33	34.39	0.004	32.92	167.73
Heterologous reactions
1 antigen subtype	Reference
2 antigen subtypes	461.50	17.87	<0.001	426.47	496.53
3 antigen subtypes	938.01	32.68	<0.001	873.97	1002.06
4 antigen subtypes	556.89	293.45	0.058	−18.25	1132.04
Proportion of pigs positive	68.87	41.61	0.098	−12.68	150.41
Constant	−730.66	239.96	0.002	−1200.97	−260.36

There were 13,771 observations of HAIT titre (outcome) for the four antigen subtypes (H3N2, swH1N1, swH1N2 & immunogen H1N1pdm09) from 8,214 pigs sera sampled from 3629 positive herd tests. Norwegian serosurveillance data between 2009 and 2017.

Categorical predictors: Antigens & Production. Ordinal predictors: Year & Heterologous reactions (number of antigens). Continuous predictors: Proportion pigs positive.