The impact of early life exposure to Plasmodium falciparum on the development of naturally acquired immunity to malaria in young Malawian children

Table 5 Association between age at the time of malaria episode and antibody levels and seroprevalence in 18 months old children

Antigen tested/parasite isolate	No episode^a (n = 457)	≥ 1 episode before 6 months of age^a (n = 31)	p value^b	≥ 1 episode between 6 and 18 months of age^a (n = 113)	p value^b
MSP1 19 kD^c	2.36 (0.51, 5.73)	6.16 (1.92, 11.16)	0.0071	4.71 (1.43, 21.25)	< 0.0001
MSP1 19 kD^c	224 (49.0)	24 (77.5)	0.002	79 (69.9)	< 0.0001
MSP2^d	2.76 (0.79, 8.23)	5.76 (1.01, 10.55)	0.1043	3.06 (1.06, 13.97)	0.3165
MSP2^d	113 (24.7)	12 (38.8)	0.084	37 (32.7)	0.083
EBA175^e	3.49 (1.96, 17.05)	3.25 (1.89, 8.79)	0.5785	3.19 (1.93, 9.91)	0.3753
EBA175^e	50 (10.9)	3 (9.7)	0.827	16 (14.2)	0.338
Rh2A9^f	7.03 (3.97, 13.13)	8.24 (4.41, 17.32)	0.3790	7.92 (4.12, 15.87)	0.2223
Rh2A9^f	108 (23.6)	10 (32.3)	0.278	33 (29.2)	0.219
Schizont	2.95 (1.02, 7.24)	7.40 (2.24, 13.97)	0.0211	4.70 (1.77, 14.87)	0.0018
Schizont	222 (48.6)	23 (74.2)	0.006	80 (70.8)	< 0.0001
E8B^g	0 (0, 0.15)	0.03 (0, 1.11)	0.0177	0 (0, 0.26)	0.0967
E8B^g	24 (5.3)	10 (32.3)	< 0.0001	9 (7.9)	0.269
R29^g	0 (0, 0.002)	0 (0, 0.43)	0.0424	0 (0, 0.24)	0.2341
R29^g	13 (2.8)	5 (16.2)	< 0.0001	3 (2.6)	0.913
3D7^g	0 (0, 0.33)	0.01 (0, 0.37)	0.4718	0 (0, 0.42)	0.8673
3D7^g	36 (7.9)	4 (12.9)	0.324	10 (8.9)	0.734

Significant p value in italic format
^aFor each antigen represented, row 1: median antibody level (interquartile range); row 2: number of seropositive children (%)
^bp value calculated by Mann–Whitney test or Chi squared test for antibody level or seropositivity, respectively
^cMerozoite surface protein 1
^dMerozoite surface protein 2
^eErythrocyte binding antigen 175
^fReticulocyte binding protein homologue 2A
^gVariant surface antigen antibody responses