BRIEF REPORT
An ibody esponse in pa ien s admi ed o he hospi al
wi h suspec ed SARS-CoV-2 in ec ion: esul s om a mul icen e
s udy ac oss Spain
Ana Fuen es
1
&Es he Se ano-Conde
1
&Ca olina Roldán
2
&Ra ael Beni o-Ruesca
3
&G ego ia Mejías
4
&
An onio Samped o
5
&Gab iel Ma ch-Roselló
6
&Isabel Fe nández-Na al
7
&Juliana Espe alba
8
&Ma io José Rod íguez
9
&
Paula Ma ínez de Agui e
10
&Ca los Salas
11
&Ma ía Lou des Roc
12
&Luis Miguel So ia
13
&Mónica Pa a-G ande
14
&
Ma ía Dolo es Mon e o
15
&Rica do Fe nández-Roblas
16
&F ancisco F anco-Ál a ez de Luna
17
&Ca men Lozano
18
&
Fede ico Ga cía
1
Recei ed: 29 Sep embe 2020 /Accep ed: 20 Decembe 2020
#The Au ho (s) 2021
Abs ac
Aim To e alua e he se ological esponse agains SARS-CoV-2 in a mul icen e s udy ep esen a i e o he Spanish COVID
pandemic.
Me hods IgG and IgM + IgA esponses we e measu ed on 1466 samples om 1236 Spanish COVID-19 pa ien s admi ed o he
hospi al, wo comme cial ELISA ki s (Vi cell SL, Spain) based on he de ec ion o an ibodies agains he i al spike p o ein and
nucleop o ein, we e used.
Resul s App oxima ely hal o he pa ien s p esen ed an ibodies (56.8% we e IgM + IgA posi i e and 43.0% we e IgG posi i e)
as soon as 2 days a e he i s posi i e PCR esul . Se ological es posi i i y inc eased wi h ime om he PCR es , and 10 days
a e he i s PCR esul , 91.5% and 88.0% o he pa ien s p esen ed IgM + IgA and IgG an ibodies, espec i ely.
Conclusion The high alues o sensi i i y a ained in he p esen s udy om a ela i ely ea ly pe iod o ime a e hospi aliza ion
suppo he use o he e alua ed se ological assays as supplemen a y diagnos ic es s o he clinical managemen o COVID-19.
Keywo ds COVID-19 .SARS-COV-2 .IgG .IgM .IgA .Diagnosis
In oduc ion
Co ona i us disease 2019 (COVID-19) is a se e e acu e e-
spi a o y synd ome p oduced by a no el co ona i us (SARS-
CoV-2) ha has sp ead globally and e y quickly since i s i s
appea ance in Wuhan, China, in Decembe 2019 [1]. SARS-
CoV-2 is he se en h known co ona i us ha in ec s humans;
SARS-CoV, MERS-CoV, and SARS-CoV-2 can cause
*Fede ico Ga cía
ega cia@ug .es
1
Hospi al Uni e si a io Clínico San Cecilio, Ins i u o de In es igación
Ibs, A , Inno ación S/N, 18016 G anada, Spain
2
Complejo Hospi ala io de Jaén, Jaén, Spain
3
Hospi al Clínico Uni e si a io Lozano Blesa, Za agoza, Spain
4
Hospi al Uni e si a io de Bu gos, Bu gos, Spain
5
Hospi al Uni e si a io Vi gen de las Nie es, G anada, Spain
6
Hospi al Clínico Uni e si a io de Valladolid, Valladolid, Spain
7
Complejo Asis encial Uni e si a io de León, León, Spain
8
Hospi al Uni e si a io Valle de Heb ón, Ba celona, Spain
9
Hospi al Ramón y Cajal, Mad id, Spain
10
Clínica Uni e sidad de Na a a, Pamplona, Spain
11
Hospi al Uni e si a io Ma qués de Valdecilla, San ande , Spain
12
Hospi al Uni e si a io Miguel Se e , Za agoza, Spain
13
Hospi al San Ped o, Log oño, Spain
14
Complejo Hospi ala io Uni e si a io de Albace e, Albace e, Spain
15
Hospi al Uni e si a io La Paz, Mad id, Spain
16
Hospi al Uni e si a io Fundación Jiménez Díaz, Mad id, Spain
17
Hospi al Uni e si a io Juan Ramón Jiménez, Huel a, Spain
18
Hospi al Uni e si a io Vi gen del Rocío, Se illa, Spain
Eu opean Jou nal o Clinical Mic obiology & In ec ious Diseases
h ps://doi.o g/10.1007/s10096-020-04139-5
se e e disease, whe eas HKU1, NL63, OC43, and 229E a e
associa ed wi h mild espi a o y illness [2]. The i us has a
genome size o 30 kilobases ha encodes mul iple s uc u al
and nons uc u al p o eins. The s uc u al p o eins include he
spike (S) p o ein, he en elope (E) p o ein, he memb ane (M)
p o ein, and he nucleocapsid (N) p o ein.
The diagnos ic app oach o SARS-CoV-2 includes he de-
ec ion o i al RNA by eal- ime PCR (RT-PCR). Di e en
ac o s could con ibu e o alse nega i e esul s o RNA es s
wi h RT-PCR, such as insu icien amoun o i us a he si e
o sample collec ion, inco ec sample collec ion o being ou -
side in he i al eplica ion ime window [3–6]. Se ological
me hods combined wi h PCR could be o help o inc easing
he sensi i i y and accu acy o he diagnosis, especially in
pa ien s wi h nega i e RT-PCR esul s; se ology may also
help o iden i y asymp oma ic and pas in ec ions. SARS-
COV-2 se ology undoub edly helps ounde s and he immune
s a us o he popula ion and o e alua e i al sp ead [7]; hence,
se ology should be used o epidemiological s udies o in es-
iga e he a e o asymp oma ic in ec ions and o be e es i-
ma e mo bidi y and mo ali y [7]. Se ological me hods include
binding and neu aliza ion assays. Binding assays such as
ELISAs a e easilyau oma ized, and hey a e e y welladap ed
o a pandemic si ua ion; neu aliza ion assays equi e i al
cul u e, and hey mus be pe o med in a acili ies wi h highe
biosecu i y le els [8].
P elimina y s udies ha e analyzed an ibody esponses
agains SARS-COV-2. Some au ho s [2,9–12] ound ha
IgM was de ec ed on day 7 and peaked on day 28, and IgG
appea ed by day 10 and peaked on day 49, while o he s [13]
de e mined ha se ocon e sion among 173 pa ien s ook
place a median imes o 12 (IgM), 14 (IgG), and 11 (neu al-
izing an ibodies) days. The du a ion and na u e o SARS-
CoV-2 immuni y is unknown. The imescale o p o ec ion is
a c i ical de e minan o he u u e impac o he pa hogen. The
p esence o absence o p o ec i e immuni y due o in ec ion o
accina ion (when a ailable) will a ec u u e ansmission
and illness se e i y and will allow he iden i ica ion o indi-
iduals wi h p o ec i e immuni y [2,7,10,13,14].
Addi ional s udies a e needed o cha ac e ize how an i-
SARS-CoV-2 an ibodies will change o e p olonged pe iods
o ime. The p esen s udy p esen s da a om a la ge se ies o
samples co e ing bo h IgG and IgM + IgA esponses o wo o
he main i al an igenic p o eins (N and S).
Ma e ials and me hods
Pa ien s
One housand wo hund ed hi y-six pa ien s sc eened o
COVID-19 admi ed o 18 Public and P i a e Spanish
Hospi als (Clínica Uni e sidad de Na a a, Complejo
Asis encial Uni e si a io de León, Complejo Hospi ala io
Uni e si a io de Albace e, Complejo Hospi ala io de Jaén,
Hospi al Clínico Uni e si a io Lozano Blesa, Hospi al
Clínico Uni e si a io de Valladolid, Hospi al Ramón y
Cajal, Hospi al San Ped o, Hospi al Uni e si a io Clínico
San Cecilio, Hospi al Uni e si a io de Bu gos, Hospi al
Uni e si a io Fundación Jiménez Díaz, Hospi al
Uni e si a io Juan Ramón Jiménez, Hospi al Uni e si a io
La Paz, Hospi al Uni e si a io Ma qués de Valdecilla,
Hospi al Uni e si a io Miguel Se e , Hospi al Uni e si a io
Valle de Heb ón, Hospi al Uni e si a io Vi gen de las Nie es,
and Hospi al Uni e si a io Vi gen del Rocío) we e s udied.
All pa ien s we e posi i e by RT-PCR; sex da a we e a ailable
o 513 men and 353 women; age da a we e a ailable o 1066
pa ien s, mean age 64 yea s, ange 15–100 yea s.
Se um samples
Samples we e d awn on he same day o a e he RT-PCR es
was pe o med. Di e ences in days we e due o clinical needs
in he gene al managemen o he pa ien s.
Single se um samples we e ob ained om 1054 pa-
ien s, while mul iple se um samples (n= 413) we e
ob ained om 183 pa ien s, comp ising 1467 samples.
The dis ibu ion o samples acco ding o ime om
RT-PCR can be seen in Table 1. The e we e wo sam-
ples a ailable o 43 pa ien s, he i s collec ed be o e 4
days a e PCR and he second collec ed 7–17 days
a e PCR.
ELISAs
An i-SARS-CoV-2 IgG and IgM + IgA ELISAs (Vi cell SL,
Spain) we e ca ied ou acco ding o he manu ac u e ’sp o-
ocol. Reac ion wells in bo h assays we e coa ed wi h nucleo-
capsid and spike p o eins. Se um samples we e p e iously
inac i a ed a 56 °C o 30 minu es. Samples we e immedia e-
ly es ed a e inac i a ion o s o ed a 4 °C o no longe han
4 days be o e es ing. The speci ici y decla ed by he manu-
ac u e o he IgG and IgM + IgA assays is 98.2% and
98.9%, espec i ely, based on s udies pe o med on
p epandemic popula ions. Bo h ELISAs a e quali a i e; he
IgM + IgA ELISA does no di e en ia e be ween bo h
inmunoglobulins.
RT-PCR assays
RT-PCR om naso- and o o-pha yngeal swabs was pe -
o med a e nucleic acid ex ac ion wi h di e en comme cial
CE-app o ed assays.
Eu J Clin Mic obiol In ec Dis
S a is ical analysis
S a is ical analysis was pe o med wi h he help o he R p o-
g am e sion 3.6.3 (2020-02-29)—“Holding he Windsock”
Copy igh (C) 2020 The R Founda ion o S a is ical
Compu ing Pla o m: x86_64-w64-mingw32/x64 (64-bi ).
Bo de line esul s we e p ima ily in e p e ed as nega i e.
The Wilcoxon-Mann-Whi ney es was used o p- alue cal-
cula ions. Da a we e g aphically p esen ed in box-and-
whiske plo s wi h boxes encompassing 90% o he da a and
whiske s p esen ing he 95% and 5% pe cen iles.
Resul s
An i-SARS-CoV-2 an ibody kine ics
The esul s om 1467 se um samples om PCR-posi i e pa-
ien s e e ed o he collec ion da e wi h espec o he i s
PCR-posi i e esul o he pa ien a e shown in Table 1.A day
0, a highe eac i i y was obse ed o IgM + IgA (154 pos-
i i e samples, 47.2%) han o IgG (135, 41.4%), wi h 187
samples (57.4%) wi h any se ological ma ke . This endency
o a highe eac i i y in he IgM + IgA esponse only eached
s a is ical signi icance a day 1 (p= 0.016), and could be seen
du ing he i s 16 days, wi h 84.0% o IgM + IgA posi i e
esul s agains 74.0% o IgG posi i e esul s a day 7 a e
PCR. A e he hi d week, he p opo ion o posi i e esul s
was simila in bo h pa ame e s, while IgG was mo e p e alen
in samples collec ed one mon h a e PCR. Posi i e IgM + IgA
oge he wi h posi i e IgG was he mos equen ly ound
pa e n (36.5%) a day 0, ollowed by posi i i y o only IgM
+ IgA (11.7%) and posi i i y o only IgG (5.8%). Th oughou
all he ime anges s udied and whene e a single ma ke was
p esen , IgM + IgA was mo e equen han IgG.
Figu e 1shows he e olu ion o IgG and IgM + IgA o e
ime. The p opo ion o posi i e cases was highe o IgM + IgA
un il day 24, when posi i i y o bo h IgG and IgM was equal.
To be e unde s and he kine ics o he an ibody esponse,
se ocon e sion was s udied in 43 pa ien s o whom wo sam-
ples we e a ailable (T1: samples collec ed no la e han 4
days pos PCR; T2, second samples collec ed be ween 7 and
17 days pos PCR). The esul s a e shown in Table 2. IgG was
de ec ed in 15 (34.9%) o he T1 samples, while IgM + IgA
was de ec ed in 23 (53.5%). IgG and IgM + IgA we e de ec ed
in 35 (81.4%) and 40 (93.0%) o he T2 samples, espec i ely.
Twen y pa ien s se ocon e ed o IgG and 19 o IgM + IgA,
whe eas 2 pa ien s did no show se ocon e sion. The index
means we e 1.97 (IgG) and 2.55 (IgM + IgA) o he acu e
in ec ion samples and 3.04 (IgG) and 3.15 (IgM + IgA) o he
con alescen samples.
E ec o age and sex on an ibody esponses o SARS-
CoV-2
PCR-posi i e pa ien s we e classi ied in o ou g oups acco d-
ing o he esul s o he se ological es s: only IgG posi i e,
only IgM + IgA posi i e, posi i e in bo h es s o nega i e in
bo h es s. Figu e 2a shows he dis ibu ion o se ological e-
sul s by age g oup co esponding o he 1066 pa ien s o
Table 1 Posi i e a es o IgG and IgA + IgM de ec ion in 1466 se um samples om PCR-posi i e pa ien s. The esul s a e exp essed as absolu e
equencies (pe cen age shown in pa en heses) o posi i e samples in each pa ame e o in bo h pa ame e s a he same ime
Sample day
a
To al no.
o se a
IgG IgM + IgA IgG and/o
IgM + IgA
Only IgG posi i e Only IgM
+IgAposi i e
Bo h IgG and IgM
+IgAposi i e
Bo h IgG and IgM
+ IgA nega i e
0 326 135 (41.4) 154 (47.2) 187 (57.4) 19 (5.8) 38 (11.7) 116 (35.6) 153 (46.9)
1 332 134 (40.4) 165 (49.7)
b
180 (54.2) 21 (6.3) 52 (15.7) 113 (34.0) 146 (44.0)
2 154 83 (53.9) 98 (63.6) 95 (61.7) 6 (3.9) 21 (13.6) 77 (50.0) 50 (32.5)
3 106 61 (57.5) 68 (64.2) 69 (65.1) 8 (7.5) 15 (14.2) 53 (50.0) 30 (28.3)
4 111 79 (71.2) 89 (80.2) 92 (82.9) 7 (6.3) 17 (15.3) 72 (64.9) 15 (13.5)
5 51 40 (78.4) 42 (82.4) 39 (76.5) 2 (3.9) 4 (7.8) 38 (74.5) 7 (13.7)
6 53 34 (64.2) 38 (71.7) 38 (71.7) 1 (1.9) 5 (9.4) 33 (62.3) 14 (26.4)
7 50 37 (74.0) 42 (84.0) 41 (82.0) 1 (2.0) 6 (12.0) 36 (72.0) 7 (14.0)
8 42 26 (61.9) 33 (78.6) 32 (76.2) 1 (2.4) 8 (19.0) 25 (59.5) 8 (19.0)
9 30 20 (66.7) 23 (76.7) 23 (76.7) 1 (3.3) 4 (13.3) 19 (63.3) 6 (20.0)
10–16 129 114 (88.4) 119 (92.2) 118 (91.5) 2 (1.6) 7 (5.4) 112 (86.8) 8 (6.2)
17–23 40 36 (90.0) 36 (90.0) 38 (95.0) 1 (2.5) 1 (2.5) 35 (87.5) 3 (7.5)
24–30 16 16 (100) 16 (100) 16 (100) 0 (0.0) 0 (0.0) 16 (100) 0 (0.0)
> 30 26 24 (92.3) 20 (76.9) 24 (92.3) 4 (15.4) 0 (0.0) 20 (76.9) 2 (7.7)
a
Days a e he i s posi i e PCR esul
b
p= 0.016 compa ed o IgG (all o he compa isons no signi ica i e)
Eu J Clin Mic obiol In ec Dis
whom age da a we e a ailable. The p opo ion o pa ien s wi h
nega i e se ological esponses o bo h es s inc eased wi h
pa ien age. When hese esul s we e analyzed acco ding o
he ime elapsed be ween he PCR and he se um collec ion
(Fig. 2b and c), his e ec could also be seen o samples
collec ed ea ly a e he i s PCR diagnosis, while mos sam-
ples collec ed in he second week a e PCR showed posi i e
se ological esponses in all age g oups.
Figu e 3shows he di e ences in se ological esul s by age
and sex. No signi ican di e ences we e seen be ween men
and women as a whole ei he o IgG o o IgM + IgA.
Al hough di e ences be ween he sexes could be obse ed
o some age g oups, he e was no a clea endency ha sup-
po ed a highe se ological esponse o men o e women, and
his esul may e lec di e ences in he popula ion sizes.
Discussion
The u ili y o se ological es s o help in he diagnosis o
COVID-19 was e alua ed in a mul icen e s udy wi h a la ge
se ies o samples collec ed om 1236 pa ien s in se e al
Spanish hospi als du ing he peak o he pandemic. In ou
s udy, we obse ed high alues o sensi i i y, especially o
he IgM + IgA es a ea ly pe iods o ime a e hospi aliza ion
(61.7% p esen ed a posi i e se ology in he i s 4 days o he
diagnosis, and 90.5% a e he i s week). We belie e ha ou
indings suppo he use o se ological assays as supplemen-
a y diagnos ic es s o he clinical managemen o COVID-
19. We also obse ed a dec eased sensi i i y o se ology in
olde pa ien s in samples collec ed ea ly in he disease.
Twocomme cialki swe eused omeasu e heIgG
and IgM + IgA esponses agains wo majo an igenic
componen s o he i us, he N and S p o eins. To ou
knowledge, ew comme cial es s a e simul aneously
basedonbo hp o eins.S udieswi hgoodpe o mances
o assays based ei he on he N p o ein [15,16], he S
p o ein [7,13,17]o bo han igens[9,10,14,18]ha e
been published. Ano he peculia i y o he assays used in
he s udy is he inclusion o IgA oge he wi h IgM o
ea ly de ec ion o he disease. Se e al s udies ha e de-
sc ibed a good sensi i i y o his immunoglobulin class,
be e han ha o IgG, al hough wi h a lowe speci ici y
[2,7,12,18,19]. The speci ici y o he es was
es ablished by he manu ac u e o he ki on he basis
o samples collec ed om p epandemic popula ions
(98.8% CI 95% 95.52–99.68). The high le els o sensi-
i i y epo ed in he p esen s udy, abo e hose epo ed
in o he s udies [17,20,21], may be ela ed o he a o e-
men ioned special ea u es o he assays used in he s udy:
he use o wo i al an igens and he inclusion o IgA.
The pe cen age o IgM + IgA-posi i e pa ien s wi h IgG-
nega i e le els was highe in samples collec ed a ea ly s ages
o he disease, as can be expec ed o hese immunoglobulin
classes. Howe e , we did no obse e a dec ease in IgM + IgA
alues, as has been shown by o he au ho s [9], p obably due
o he low numbe o samples a e hospi al discha ge included
in he s udy. Posi i i y o he se ological es s inc eases wi h
ime, eaching alues close o 100% in samples aken 10 days
o mo e a e he i s PCR esul . Con e sely, in s udies ca -
ied ou wi h MERS pa ien s, 20% o he pa ien s did no show
Fig. 1 Dynamic end o he
posi i e a e o IgG and IgM +
IgA in se a o RT-PCR-posi i e
pa ien s
Table 2 Posi i e a es o IgG and IgA + IgM de ec ion in se a om
selec ed pa ien s o whom wo samples collec ed a wo di e en ime
poin s we e a ailable. Time anges we e 0–4 days pos PCR o i s
se um collec ion and 7–17 days pos PCR o second se um collec ion
Se ological pa ame e No. o posi i e se a (%)
0–4days 7–17 days
IgG 15(34.9) 35(81.4)
IgM + IgA 23 (53.5) 40 (93.0)
Bo h IgG and IgM + IgA 15 (34.9) 34 (79.1)
IgG only 1 (2.3) 1 (2.3)
IgM + IgA only 8 (18.6) 6 (14.0)
Bo h nega i e 19 (44.2) 2 (4.7)
T1 i s se um, T2 second se um
Eu J Clin Mic obiol In ec Dis
a de ec able se ological esponse a e mo e han 30 days o
e olu ion [22]. Fo SARS, all pa ien s de eloped an ibodies
[23], bu 28% showed nega i e IgM a e 60 days [24], and
mos pa ien s had los he an ibody esponse by six yea s [25].
Howe e , i is su p ising ha he la ge p opo ion o pa-
ien s wi h posi i e IgG le els in samples we e su eyed so
close o he i s PCR-posi i e esul s: 45.0% wi hin he i s 3
days. Some o he pa ien s e en debu ed wi h an IgG-posi i e/
IgM + IgA-nega i e pa e n. This inding could be in ag ee-
men wi h p e ious con ac wi h o he co ona i uses showing
an igenic simila i ies wi h he no el SARS-CoV-2, as has
been ound by au ho s s udying immune cell esponses [26],
and i could also be explained by he ac ha pa ien s a e
a ending he eme gency oom and need hospi aliza ion, sug-
ges ing ad anced disease. Howe e , i is no in ag eemen
wi h he e y low le els o IgG agains he spike p o ein and
Fig. 2 Se ology es esul s o posi i e PCR pa ien s g ouped by age. Ba
heigh s ep esen absolu e equencies. aDa a om all PCR-posi i e pa-
ien s, b esul s co esponding o samples collec ed in he i s week a e
he i s PCR esul , and c esul s co esponding o samples collec ed la e
han one week a e he i s PCR esul
Fig. 3 IgG and IgM + IgA index alue (10 X se um/cu o ) boxplo o all PCR-posi i e pa ien s dis inguishing be ween male and emale and g ouped
by age. Boxes encompass 90% o he da a, and whiske s p esen he 95% and 5% pe cen iles
Eu J Clin Mic obiol In ec Dis

nucleop o ein ound in he p epandemic popula ion ha ans-
la es o he e y high speci ici y o he se ological assays used
in his and o he s udies [27].
Due o he la ge se ies o se a s udied, se ological esul s
could be s a i ied acco ding o he age o he pa ien s. A
dec eased numbe o pa ien s wi h posi i e se ology was ob-
se ed among he olde pa ien s o samples collec ed ea ly in
he disease. Howe e , he p opo ion inc eased o nea 100%
posi i i y in all age g oups o samples collec ed in he second
week o la e a e he i s posi i e PCR esul . Some au ho s
ha e sugges ed a ela ionship be ween his delayed esponse
in elde ly indi iduals, wi h less a o able disease e olu ion in
his popula ion g oup [28]. Fo he compa ison o se ological
esponses be ween men and women, no global signi ican
di e ences we e obse ed ei he in he p opo ion o posi i e
esul s o in he immunoglobulin le els a ained ineach g oup.
The low numbe o samples in some o he subg oups may
ha e limi ed he s a is ical po ency o he compa isons.
In summa y, he high alues o sensi i i y a ained in he
p esen s udy om a ela i ely ea ly pe iod o ime a e hos-
pi aliza ion suppo he use o he e alua ed se ological assays
as supplemen a y diagnos ic es s o he clinical managemen
o COVID-19. The la ge numbe o samples gi es a pa icula
s eng h o he e alua ion compa ed wi h ha o o he s p e i-
ously published. Howe e , he lack o clinical and e olu ion-
a y da a o he pa ien s, as well as ha ing used ime om
posi i e PCR esul a he han ime om symp om onse ,
cons i u es i s majo limi a ions.
Acknowledgmen s We acknowledge Vi cell SL o hei echnical
suppo in he se ological assays. We also hank all o he heal hca e
wo ke s hei inc edible e o s and i eless commi men du ing his
pandemic.
Au ho s’con ibu ions Ana Fuen es and Es he Se ano-Conde: da a col-
lec ion, sample p ocessing, da a analysis, d a ing o he manusc ip .
Ca olina Roldán, Ra ael Beni o-Ruesca, G ego ia Mejías, An onio
Samped o, Gab iel Ma ch-Roselló, Isabel Fe nández-Na al, Juliana
Espe alba Esque a, Ma io José Rod íguez, Paula Ma ínez de Agui e,
Ca los Salas Vene o, Ma ía Lou des Roc, Luis Miguel So ia, Mónica
Pa a-G ande, Ma ía Dolo es Mon e o, Rica do Fe nández-Roblas,
F ancisco F anco-Ál a ez de Luna, Ca men Lozano: da a collec ion,
sample p ocessing, e iewing o he manusc ip .
Fede ico Ga cía: da a analysis, d a ing o he manusc ip , e iewing,
and edi ing o he manusc ip .
Funding The ELISA ki s o he IgG and IgM + IgA assays we e p o-
ided by Vi cell SL. No addi ional unding was ecei ed.
Da a a ailabili y Da a may be p o ided upon eques o he co espond-
ing au ho .
Compliance wi h e hical s anda ds
E hical app o al, consen o pa icipa e, consen o publish Se a we e
anonymized and sou ced om emnan specimens. The Spanish Heal h
Minis y issued a special au ho iza ion o he collec ion o hese samples
du ing he pandemic pe iod in Spain o suppo he e alua ion o new
diagnos ic es s.
Compe ing in e es All au ho s decla e no con lic o in e es o he
subjec o he s udy
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Publishe ’sno eSp inge Na u e emains neu al wi h ega d o ju isdic-
ional claims in published maps and ins i u ional a ilia ions.
Eu J Clin Mic obiol In ec Dis