Article

Systemic Adverse Effects Induced by the BNT162b2 Vaccine
Are Associated with Higher Antibody Titers from 3 to 6 Months
after Vaccination
Ryousuke Koike 1,2 , Michiru Sawahata 1,3, * , Yosikazu Nakamura 4 , Yushi Nomura 1,2 , Otohiro Katsube 1 ,Koichi Hagiwara 3 , Seiji Niho 2 , Norihiro Masuda 5 , Takaaki Tanaka 6 and Kumiya Sugiyama 1,7
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Citation: Koike, R.; Sawahata, M.;
Nakamura, Y.; Nomura, Y.; Katsube,O.; Hagiwara, K.; Niho, S.; Masuda,N.; Tanaka, T.; Sugiyama, K. Systemic
Adverse Effects Induced by the
BNT162b2 Vaccine Are Associatedwith Higher Antibody Titers from 3
to 6 Months after Vaccination.
Vaccines 2022, 10, 451. https://doi.org/10.3390/vaccines10030451
Academic Editor: Moriya Tsuji
Received: 23 January 2022
Accepted: 13 March 2022
Published: 15 March 2022
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims inpublished maps and institutional affiliations.

Copyright: © 2022 by the authors.
Licensee MDPI, Basel, Switzerland.

*

Department of Respiratory Medicine and Clinical Immunology, National Hospital Organization Utsunomiya
National Hospital, Utsunomiya 329-1193, Japan; ryosuke@dokkyomed.ac.jp (R.K.);
nomura.yushi.wv@mail.hosp.go.jp (Y.N.); katsube.otohiro.qy@mail.hosp.go.jp (O.K.);
sugiyama@dokkyomed.ac.jp (K.S.)
Department of Pulmonary Medicine and Clinical Immunology, Dokkyo Medical University,
Shimotsuga 321-0293, Japan; siniho@dokkyomed.ac.jp
Division of Pulmonary Medicine, Department of Medicine, Jichi Medical University, Shimotsuke 329-0498,
Japan; hagiwark@jichi.ac.jp
Department of Public Health, Jichi Medical University, Shimotsuke 329-0498, Japan; nakamuyk@jichi.ac.jp
Department of Surgery, National Hospital Organization Utsunomiya National Hospital,
Utsunomiya 329-1193, Japan; masuda.norihiro.nt@mail.hosp.go.jp
Department of Orthopaedic Surgery, National Hospital Organization Utsunomiya National Hospital,
Utsunomiya 329-1193, Japan; tanaka.takaaki.vh@mail.hosp.go.jp
Department of Respiratory Medicine and Clinical Immunology, Saitama Medical Center, Dokkyo Medical
University, Shimotsuga 321-0293, Japan
Correspondence: sawahata@jichi.ac.jp; Tel.: +81-285-587-350

Abstract: Objective: We aimed to determine the relationship between vaccine-related adverse effects
and antibody (Ab) titers from 3 to 6 months after the second dose of the BNT162b2 coronavirus disease2019 (COVID-19) mRNA vaccine (Pfizer/BioNTech) in Japan. Methods: We enrolled 378 healthcare
workers (255 women and 123 men) whose Ab titers were analyzed 3 and 6 months after the second
dose in our previous study and whose characteristics and adverse effects were collected previously
by using a structured self-report questionnaire. Results: The workers’ median age was 44 years.
Although injection-site symptoms occurred with almost equal frequency between the first andsecond doses, systemic adverse effects, such as general fatigue and fever, were significantly more
frequent after the second dose than after the first dose. Multivariate analysis showed that fever was
significantly correlated with female participants for the second dose (odds ratio (OR), 2.139; 95%
confidence interval (95% CI), 1.185–3.859), older age for the first dose (OR, 0.962; 95% CI, 0.931–0.994)
and second dose (OR, 0.957; 95% CI, 0.936–0.979), and dyslipidemia for the first dose (OR, 8.750; 95%
CI, 1.814–42.20). Age-adjusted Ab titers at 3 months after vaccination were 23.7% and 23.4% higher inpatients with a fever than in those without a fever after the first and second dose, respectively. In
addition, age-adjusted Ab titers at 3 and 6 months after the second dose were, respectively, 21.7% and19.3% higher in the group in which an anti-inflammatory agent was used than in the group without
the use of an anti-inflammatory agent. Conclusion: Participants with systemic adverse effects tend tohave higher Ab titers from 3 to 6 months after the second dose of the BNT162b2 vaccine. Our results
may encourage vaccination, even among people with vaccine hesitancy related to relatively common
systemic adverse effects.
Keywords: SARS-CoV-2; viral infection; clinical epidemiology; adverse effectThis article is an open access article
distributed under the terms andconditions of the Creative Commons
Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

1. Introduction
The BNT162b2 vaccine (Pfizer/BioNTech, NY, USA / Mainz, Germany) was selected
as the first coronavirus disease 2019 (COVID-19) mRNA vaccine to be administered to

Vaccines 2022, 10, 451. https://doi.org/10.3390/vaccines10030451

https://www.mdpi.com/journal/vaccines

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healthcare professionals in Japan, beginning in February 2021. The vaccine helps to prevent
not only the onset [1] but also the progression of COVID-19. However, some people hesitatein getting vaccinated due to fear of relatively common adverse effects that occur shortly
after vaccination with the BNT162b2 vaccine [2–4].
If the maximum vaccine efficacy, including antibody (Ab) responses, is guaranteed,most people will accept a certain severity of vaccination-related adverse effects [2]. Although several reports concluded that there is no correlation or only low correlation
between adverse effects and the Ab titers detected immediately after vaccination [5–8], acorrelation is expected between adverse effects and the Ab titers detected several months
after vaccination [9]. Antibody titers alone do not correlate perfectly with protection because the benefits of mRNA vaccines include not only B-cell/humoral responses but also
T-cell/cell-mediated immunity. To examine the efficacy of vaccination, it is more importantto analyze the moderate-term levels of Ab titers after vaccination rather than the peak Abtiter obtained shortly after vaccination. Indeed, some reports [6,10] have suggested thatsystemic adverse effects may be induced as a hypersensitive immune reaction relative tothe accumulation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike
protein itself immediately after injection of the first mRNA vaccine dose rather than tochemical additives in vaccines. The analysis of the response to the first vaccine dose in persons with a previous COVID-19 infection revealed that Ab titers were 10 to 45 times higher
in individuals with preexisting immunity than in those without preexisting immunity at
the same time points after the first vaccine dose [10]. Interestingly, systemic adverse effects,
including fatigue, headache, chills, muscle pain, fever, and joint pain, were more common
among participants with preexisting immunity whereas local adverse effects occurred withsimilar frequency among participants with and without preexisting immunity [10].
In our previous studies [11,12], we showed that the most important factors associatedwith lower Ab titers at 3 and 6 months were age and smoking, probably reflecting their effecton peak Ab titers, and that the only factor significantly associated with the attenuation in the
Ab titer from 3 to 6 months was sex, which reduced the sex difference seen during the first
3 months. Against this background, we analyzed the relationship between adverse effects
and Ab titers against the SARS-CoV-2 spike antigen from 3 to 6 months after vaccination
with the BNT162b2 vaccine in Japan. This study is expected to contribute to maximizing
the efficacy of vaccination while minimizing adverse effects as a step toward optimizing
and individualizing the vaccination regimen.
2. Methods
2.1. Population and Study Design
In our previous single-center prospective observational study [11,12], we enrolled
378 healthcare workers (255 women and 123 men) at the National Hospital Organization
Utsunomiya National Hospital in the Tochigi Prefecture, Japan, and analyzed their Ab
titers at 3 and 6 months after the second of two BNT162b2 vaccine inoculations, which wereadministered 3 weeks apart in February and March 2021. The participants’ characteristics
and adverse effects were collected by using a structured self-report questionnaire 2 months
after the second dose of the vaccine, and in this study, we analyzed the relationships ofadverse effects with Ab titers at 3 and 6 months.
In our previous study [11], we used the participants’ blood samples to measure total
Ab titers against the SARS-CoV-2 spike antigen by using a commercially available electrochemiluminescence immunoassay (Elecsys® Anti-SARS-CoV-2 RUO; Roche Diagnostics,
Basel, Switzerland) [13]. In addition to their clinical and demographic characteristics,
adverse effects occurring shortly after the first and second doses were recorded in thatstudy by using a structured self-report questionnaire [11]. In total, 365 healthcare workers(250 women and 115 men) remained after the exclusion of 10 participants whose blood
samples were not obtained at 6 months and 3 participants whose blood samples confirmed
the presence of Abs against the nucleocapsid proteins for SARS-CoV-2 [12]; the blood samples of these 365 participants were used to measure total Ab titers against the SARS-CoV-2

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spike antigen 6 months after the second dose. The relationships between Ab titers against
the SARS-CoV-2 spike antigen and clinical and lifestyle characteristics were analyzed. In
the age-adjusted analysis, individual Ab titers were recalculated by subtracting the median
Ab titer of the corresponding age group from an individual’s Ab titer. For example, anage-adjusted Ab titer for an individual in his/her 20s was calculated as follows: individual
Ab titer − median Ab titer for participants in their 20s.
The Ethics Committee of the National Hospital Organization Utsunomiya National
Hospital (No. 03-01; 19 April 2021) approved this study, and written informed consent was
obtained from all participants before their enrollment.
2.2. Structured Self-Report Questionnaire to Obtain Individual Variables
Adverse effects in response to the first and second doses of the BNT162b2 vaccine,
as well as clinical history and demographic characteristics, were collected by means ofa structured self-report questionnaire. The maximum body temperature induced by the
BNT162b2 vaccine was taken under armpits and included in the questionnaire. In addition,
we asked participants about the use of an anti-inflammatory agent for adverse effects
induced by the BNT162b2 vaccine. However, the preventive use of acetaminophen was
excluded.
2.3. Data Analysis
Nonparametric continuous data were expressed as the median with the interquartile range (IQR). Categorical data were presented as absolute numbers (n) and relative
frequencies (%). We used Microsoft® Excel® 2016 MSO (Microsoft Corp., Redmond, WA,
USA). To calculate Spearman’s rank correlation coefficient and perform the Mann–Whitney
U test, chi-square test, and multivariate logistic regression analysis, we used Statistical
Package for Social Sciences (SPSS) version 28 (IBM Japan, Ltd., Tokyo, Japan). Univariate
and multivariate logistic regression models were applied to analyze the relationship between SARS-CoV-2 Ab or fever as the dependent variable and adverse effects or clinicalparameters as the independent variables.
3. Results
3.1. Incidence of Adverse Effects in Response to the BNT162b2 Vaccine
The participants’ baseline characteristics were reported in our previous publications [11,12]. In total, 378 healthcare workers (255 women and 123 men) were enrolled [11],and the median age (IQR) of the participants was 44 (32–54) years. Nurses (n = 177) andphysicians (n = 38) comprised 56.9% of the study population. Overall, the vaccine hadno adverse effects resulting in hospitalization. The prevalence of adverse effects and theanti-inflammatory agent used in response to the BNT162b2 vaccine is shown in Table 1.
The prevalence of each was higher after the second vaccine dose than after the first dose(chi-square test, p < 0.01). Local adverse effects occurred with almost equal frequency forthe first and second doses. The rates of concordance, in which the same reactions wereseen for both the first and second doses, were higher for systemic reactions than for local
reactions.

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Table 1. Prevalence of adverse effects induced by the BNT162b2 vaccine (n = 378).
Adverse Effects
Systemic reactions
Fever ≥ 37.0 ◦ C
General fatigue
HeadacheMuscle pain
Joint pain
NauseaDiarrhea
Local reactions
Pain
Swelling
Induration
Itching
Acetaminophen use

After First Dose

After Second Dose

Rate of Concordance
between 1st and 2nd

17.0% (56/274/48)
35.0% (132/245/1)
20.7% (78/299/1)
18.6% (70/307/1)
7.7% (29/348/1)
2.4% (9/368/1)
1.1% (4/373/1)

56.8% (191/145/42)
73.3% (277/101/0)
46.0% (173/203/2)
35.7% (135/243/0)
33.2% (125/252/1)
7.0% (26/347/5)
3.7% (14/362/2)

83.9% (47/56)
93.9% (124/132)
79.5% (62/78)
80.0% (56/70)
86.2% (25/29)
66.7% (6/9)
50.0% (2/4)

89.6% (337/39/2)
31.6% (119/257/2)
23.4% (88/288/2)
16.5% (62/314/2)
21.1% (76/284/18)

83.3% (310/62/6)
31.1% (117/259/2)
21.0% (79/297/2)
17.2% (65/313/0)
57.1% (210/158/10)

87.2% (294/337)
74.8% (89/119)
72.7% (64/88)
72.6% (45/62)
76.3% (58/76)

Data show the percentage of positive reactions (number of yes/no/unknown).

3.2. Relationship between Participants’ Characteristics and Vaccine-Related Systemic Adverse
Effects
Fever is one of the most common systemic adverse effects, and we used multivariate
logistic regression analysis to investigate whether participants’ characteristics were risk
factors for the occurrence of fever (Table 2). Fever was defined as a maximum bodytemperature of 37.0 ◦ C or higher. The multivariate analysis revelaed that the female sex(odds ratio (OR), 2.139; 95% confidence interval (95% CI), 1.185–3.859) was correlated withthe occurrence of fever after the second dose. Patients of a younger age also correlated withthe occurrence of fever after the first dose (OR, 0.962; 95% CI, 0.931–0.994) and second dose
(OR, 0.957; 95% CI, 0.936–0.979). A scatter plot of the distribution of body temperatureby age showed that younger participants had a significantly higher body temperature
shortly after both the first and second doses (correlation coefficient ρ = −0.370 and −0.184,
respectively) (Figure 1). Dyslipidemia was also correlated with fever after the first dose (OR,8.750; 95%CI, 1.815–42.25), but no other clinical or lifestyle characteristics were correlatedwith fever.
Table 2. Multivariate logistic regression analysis of risk factors associated with fever (≥37.0 ◦ C)
(n = 378).
After the First Dose
Risk Factors
Sex (female)Age (older)
BMI (obesity)
Smoking
Drinking
Any allergic history
Food
Drug or chemical
Any allergic disease
Allergic rhinitis
AsthmaAtopic dermatitis/Urticaria
Diabetes mellitus
Hypertension
Dyslipidemia
Collagen diseases

After the Second DoseOR

95% CIOR

95% CI

1.862
0.962
1.054
0.677
0.738
0.702
0.748
0.955
0.804
3.368
1.695
1.869
5.979
0.522
8.750
2.727

0.789–4.392
0.931–0.994
0.966–1.149
0.303–1.510
0.349–1.563
0.268–1.842
0.207–2.700
0.247–3.696
0.155–4.183
0.751–15.12
0.602–4.768
0.703–4.968
0.953–37.50
0.085–3.193
1.814–42.20
0.629–11.83

2.139
0.957
0.995
1.616
0.584
1.312
1.088
1.018
3.125
0.455
0.955
0.757
1.457
0.525
2.284
3.501

1.185–3.859
0.936–0.979
0.929–1.066
0.913–2.863
0.338–1.010
0.629–2.736
0.411–2.879
0.368–2.813
0.918–10.64
0.145–1.428
0.389–2.347
0.323–1.774
0.287–7.411
0.159–1.732
0.593–8.804
0.690–17.76

Vaccines 2022, 10, 451

5 of 10Figure 1. Relationships between age and body temperature after the first (A) and second (B) vaccine
doses. Significant negative correlations were observed after both the first and second vaccine doses.
(A: n = 176; B: n = 243).

3.3. Association between Ab Titers and Vaccine-Related Adverse Effects
We analyzed the relationship between Ab titers at 3 and 6 months after vaccination
and adverse effects after the first and second vaccine doses (Tables 3 and 4). Age-adjusted
Ab titers were used because the titers significantly differed between younger and older
participants at 3 and 6 months after vaccination. Fever after both the first and second doses
was associated with a significantly higher Ab titer at 3 months after vaccination. A scatterplot of the distribution of body temperature by Ab titer also showed that participants witha high body temperature as an adverse effect after the second dose had a significantly
higher Ab titer at 3 months after vaccination but not at 6 months (correlation coefficientsVaccines 2022, 10, 451

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ρ = 0.166 and −0.102, respectively) (Figure 2). General fatigue and joint pain after the first
and/or second vaccine doses were associated with significantly higher Ab titers at both3 and 6 months after vaccination. Nausea after the second vaccine dose was associatedwith a significantly higher Ab titer at 6 months after vaccination. In addition, the use of ananti-inflammatory agent after the second vaccine dose was significantly associated withhigh Ab titers at both 3 and 6 months after vaccination. However, local reactions were notassociated with Ab titers.
Table 3. Relationship between adverse effects and age-adjusted antibody titers at 3 months after
vaccination (n = 378).
Adverse Effects
Systemic reactions
Fever (≥37.0 ◦ C)
General fatigue *Headache *Muscle pain *Joint pain *Nausea *Diarrhea *Local reactions
Pain *
Swelling *Induration *Itching *Acetaminophen use *After the First DoseMedian (IQR) U/mL

p-Value

After the Second DoseMedian (IQR) U/mL

p-Value

153 (−242 to 529)/−28 (−306 to 293)
22 (−337 to 369)/0 (−279 to 334)
−30 (−416 to 334)/0 (−285 to 355)
32 (−329 to 395)/0 (−293 to 341)
189 (−133 to 751)/−13 (−308 to 321)
145 (−516 to 369)/0 (−299 to 340)
418(120 to 691)/0 (−299 to 340)

0.042
0.841
0.289
0.770
0.014
0.926
0.295

110 (−259 to 511)/−69 (−335 to 263)
60 (−287 to 430)/−109 (−327 to 130)
70 (−309 to 481)/−47 (−293 to 297)
90 (−246 to 340)/−39 (−336 to 352)
147 (−140 to 510)/−72 (−370 to 275)
−249 (−441 to 171)/9 (−285 to 353)
−91 (−413 to 376)/1 (−296 to 341)

0.002
0.010
0.120
0.058
<0.001
0.088
0.430

2 (−308 to 369)/−88 (−256 to 237)
0 (−307 to 395)/−3 (−299 to 317)
38 (−293 to 510)/−1 (−299 to 318)
81 (−174 to 451)/−17 (−309 to 339)
108 (−281 to 632)/−17 (−299 to 292)

0.498
0.822
0.289
0.265
0.136

−1 (−317 to 341)/26 (−226 to 335)
0 (−312 to 411)/−11 (−293 to 322)
−18 (−311 to 316)/0 (−299 to 339)
9 (−273 to 269)/0 (−301 to 364)
82 (−256 to 517)/−84 (−371 to 226)

0.528
0.780
0.902
0.896
<0.001* Yes/no are shown.

Table 4. Relationship between adverse effects and age-adjusted antibody titers at 6 months after
vaccination (n = 365).
Adverse Effects
Systemic reactions
Fever (≥37.0 ◦ C)
General fatigue *Headache *Muscle pain *Joint pain *Nausea *Diarrhea *Local reactions
Pain *
Swelling *Induration *Itching *Acetaminophen use *After the First DoseMedian (IQR) U/mL

p-Value

After the Second DoseMedian (IQR) U/mL

p-Value60 (−181 to 343)/−11 (−227to 256)0 (−242 to 286)/1 (−223 to 263)
−28 (−290 to 290)/8 (−214 to 263)
−4 (−256 to 248)/7 (−222 to 274)
142 (−71 to 461)/−7 (−240 to 256)−56 (−339 to 314)/6 (−224 to 270)
695 (169 to 1036)/0 (−225 to 268)

0.187
0.853
0.278
0.635
0.023
0.580
0.181

57 (−201 to 359)/−25 (−229 to 207)35 (−217 to 328)/−117 (−241 to 174)
30 (−240 to 336)/−20 (−224 to 254)
33 (−178 to 288)/−19 (−241 to 265)
54 (−92 to 339)/−58 (−264 to 244)
−188 (−303 to −7)/14 (−221 to 283)
−148 (−308 to 295)/1 (−224 to 271)

0.065
0.015
0.425
0.237
0.001
0.013
0.294

9 (−240 to 274)/−55 (−186 to 144)
31 (−210 to 306)/−9 (−238 to 268)
0 (−203 to 334)/6 (−233 to 268)
37 (−169 to 358)/−9 (−239 to 268)
78 (−224 to 446)/−8 (−233 to 251)

0.441
0.543
0.697
0.304
0.191

−9 (−317 to 341)/42 (−226 to 335)
−4 (−212 to 256)/3 (−232 to 273)−49(−244 to 244)/11 (−226 to 280)
1 (−239 to 200)/0 (−224 to 281)46 (−208 to 334)/−58 (−246 to 209)

0.257
0.785
0.476
0.735
0.019

* Yes/no are shown.

Vaccines 2022, 10, 451

7 of 10Figure 2. Relationships between body temperature after the second vaccine dose and age-adjusted
anti-SARS-CoV-2 Ab titers at 3 months (A) and 6 months (B) after the second dose of the vaccine.
Significant positive correlations were observed at 3 months after vaccination but not at 6 months.
(A: n = 243; B: n = 243).

The differences in age-adjusted Ab titers at 3 months after vaccination between individuals with and without fever after the first and second doses were 181 U/mL and 179 U/mL,
respectively. These values were 23.7% and 23.4% of the median Ab titer of 746 U/mL at
3 months after vaccination. In addition, differences in the age-adjusted Ab titers between
individuals with and without anti-inflammatory agent use after the second vaccine dosewere 166 U/mL and 104 U/mL at 3 and 6 months after vaccination, respectively. These
values were 21.7% and 19.3% of the median Ab titers of 746 U/mL and 539 U/mL at 3 and6 months after vaccination, respectively.

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4. Discussion
To our knowledge, this is the first study to report the relationship between adverse
effects and Ab titers against the SARS-CoV-2 spike antigen from 3 to 6 months after
vaccination with the BNT162b2 vaccine in Japan. Three important findings were obtained.
First, although injection-site symptoms occurred with almost equal frequency for the firstand second vaccine doses, systemic reactions were significantly more common after thesecond dose (Table 1). General fatigue and fever were the first and second most common
systemic adverse effects. Second, multivariate analysis revealed significant correlationsof fever with female patients for the second dose; younger patients for both the first andsecond doses; and dyslipidemia for the first dose (Table 2). No other clinical or lifestylecharacteristics were correlated with fever. Third, regarding the relationship between
systemic adverse effects and Ab titers (Tables 3 and 4), participants with general fatigue
after the second dose had significantly higher age-adjusted Ab titers at both 3 months and6 months than those without general fatigue. Compared with participants without fever,those with fever after the first or second dose had significantly higher age-adjusted Ab
titers at 3 months but not at 6 months. Participants with joint pain after the first or second
dose had significantly higher age-adjusted Ab titers at both 3 months and 6 months thanthose without joint pain. Participants who used anti-inflammatory agents after the second
dose showed a significantly higher Ab titer.
Not only high Ab responses against SARS-CoV-2 spike protein but also systemic
adverse effects induced by the BNT162b2 vaccine were reported to be more common among
participants with preexisting immunity due to COVID-19 infection [10], suggesting thatsome systemic adverse effects are induced as a more vigorous response to the SARS-CoV-2
spike protein itself produced by the BNT162b2 vaccine. Previous publications reported thatadverse effects induced by the BNT162b2 vaccine had no correlation or only low correlation
with Ab titers detected immediately after vaccination [5–8]. However, to evaluate thelong-term effects of vaccination, research should consider Ab titers several months after
vaccination and not only the peak level of Ab titers. Accordingly, we determined therelationship between adverse effects and Ab titers from 3 to 6 months after the second
dose of the BNT162b2 vaccine. Few studies have addressed this issue, but we found one
report from Estonia showing that the Ab response was negatively correlated with age andpositively correlated with the total score for vaccination adverse effects [9].
For the second findings, we found significant correlations of the female sex, younger
age, and dyslipidemia with fever (Table 2). Some studies have reported that women andyounger people more commonly show adverse effects of the BNT162b2 vaccine [6], andour results support those findings. However, the reasons for why dyslipidemia would
be a risk factor for fever are not known. Atherogenic dyslipidemia may have effects on
the activity of collagen diseases, such as systemic lupus erythematosus and rheumatoid
arthritis [14,15]. Diabetes mellitus, a known immune disorder, was also a near-significant
risk factor for adverse effects after the first dose. These metabolic diseases complicate
immune disorders, and these immune disorders may contribute to systemic reactions after
the first vaccine dose.
Regarding the third finding, the occurrence of systemic adverse effects, including
general fatigue, fever, and joint pain, and the use of an anti-inflammatory agent for adverse
effects were significantly associated with a high Ab titer. In particular, body temperatures
recorded as an adverse effect were significantly and positively correlated with the Ab
titer at 3 months after vaccination, suggesting that the severity of systemic adverse effects
may promote a stronger ability to maintain high Ab titers against the spike protein of
this virus. Joint pain contributed to significantly higher Ab titers after both the first andsecond doses at both 3 and 6 months after vaccination. Joint pain was one of the mostcommon reactions. However, we could not find previous publications that explained therelationship between Ab titer and joint pain, and we also are unable to speculate why
Ab titers were more strongly reflected by joint pain than by fever or general fatigue. We
speculate that participants taking anti-inflammatory drugs (acetaminophen) have moreVaccines 2022, 10, 451

9 of 10systemic inflammation and, thus, have higher titers because of greater reactogenicity; thehigher titers would not be a result of anti-inflammatory medications.
Some limitations and possible sources of bias in this study include the following. First,
participants were limited in number and were all healthcare workers vaccinated at a single
national hospital in the Tochigi Prefecture. Therefore, the results obtained in this study
might not be widely generalizable or even generalizable within Japan. Second, we may
require additional analysis and discussion to determine whether age is an important factor
independently associated with adverse effects. One possibility is that fever may be an
independent factor associated with higher Ab titers but not age. In this case, because mostof the participants with fever were younger, a younger age may not be independently
associated with a higher Ab titer. The opposite is also a possibility. In addition, both fever
and age may be important factors. Therefore, we cannot determine whether fever or young
age is a more important factor. Third, individuals with systemic or local symptoms useddrugs to counter them, resulting in bias whereby some other symptoms might have been
prevented from occurring.
5. Conclusions
In conclusion, participants with systemic adverse effects had approximately 20%
higher Ab titers at 3 and 6 months after the second dose of the BNT162b2 vaccine. Although
the systemic adverse effects induced by the BNT162b2 vaccine are sometimes unpleasant,higher Ab titers should reduce the risk of a more severe COVID-19 infection. We hope that
our results will encourage vaccine uptake.
Author Contributions: Conceptualization, M.S., K.S., R.K. and Y.N. (Yosikazu Nakamura); methodology and software, R.K., K.S., M.S. and Y.N. (Yosikazu Nakamura); validation, K.S., M.S. and Y.N.
(Yosikazu Nakamura); formal analysis and investigation, K.S., R.K., M.S. and Y.N. (Yosikazu Nakamura); resources, T.T., K.S., N.M., R.K., M.S., O.K. and Y.N. (Yushi Nomura); data curation, R.K.,
K.S. and M.S.; writing original draft preparation, M.S., K.S., R.K. and Y.N. (Yosikazu Nakamura);
writing review and editing, T.T., N.M., S.N., K.H., O.K. and Y.N. (Yushi Nomura); visualization, K.S.,
R.K. and M.S.; supervision, M.S., K.S., T.T., S.N., and K.H.; project administration, K.S. and T.T.;
funding acquisition, T.T. and K.S. All authors have read and agreed to the published version of themanuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: The study was conducted according to the guidelines of the
Declaration of Helsinki and approved by the Ethics Committee of National Hospital Organization
Utsunomiya National Hospital (No. 03-01, 19 April 2021).
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.
Acknowledgments: The authors thank all staff at the National Hospital Organization Utsunomiya
National Hospital for providing support during sample collection. We would like to thank Miwa
Okada, Minako Yamagishi, Junko Shibayama, Yuko Tajima, Mami Ochiai, Midori Takahashi, Hiroko
Ueno, Natsuka Suzuki, and Yoshino Iwaya for providing support in data analysis.
Conflicts of Interest: The authors declare no conflict of interest.

Abbreviations
COVID-19: coronavirus disease 2019; Ab: antibody; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; IQR: interquartile range; OR: odds ratio; CI: confidence interval.

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