Boosting Dose of Pfizer–BioNtech mRNA Vaccine Against SARS-CoV-2 Does Not Affect Reproductive Outcomes in In-Vitro Fertilization Patients: A Cohort Study

Abstract

Background:

Since the introduction of anti-COVID-19 mRNA vaccination, few studies have shown that reproductive outcomes in artificial reproductive technology (ART) treatments are not impaired, after receiving the two-dose regimen. Our aim was to investigate whether a boosting dose of the Pfizer–BioNtech mRNA vaccine affects reproductive outcomes in ART patients.

Materials and Methods:

This is a prospective observational study, including 157 consecutive in-vitro fertilization (IVF) cycles between October 1, 2021, and November 24, 2021, in a single university affiliated IVF unit. We included female patients going through an ART procedure and male partners in cases of utilization of a fresh sperm sample. The study population was divided into four groups according to exposure status: vaccinated and boosted patients (three total doses of Pfizer–BioNtech mRNA vaccine), patients who were vaccinated without the booster dose (one or two vaccine doses), PCR-confirmed convalescent COVID-19 patients, and unvaccinated nonconvalescent patients. Main outcome measure was clinical pregnancy rate.

Results:

In total, 99 (63%) female patients were vaccinated three times, 24 (15.3%) were vaccinated without the booster dose, 21 (13.4%) were convalescent, and 13 were (8.3%) unexposed. Although age differed between study groups, vaccination exposure status did not affect treatment outcome: clinical pregnancy rates, maximal estradiol levels, and number of oocytes retrieved did not differ significantly between study groups (p = 0.78, 0.50, and 0.97, respectively). Vaccinated patients who received a boosting vaccine dose were treated within 43.3 ± 30.9 days after receiving the last dose, whereas vaccinated, nonboosted, or convalescent patients were treated 168.7 ± 53 and 209.6 ± 85.1 days after their last exposure, respectively. We stratified the male cohort according to boosting vaccine dose status. Sperm concentration and motility did not differ significantly after boosting (p = 0.49 and 0.49, respectively).

Conclusions:

Our results provide further reassurance that IVF outcomes are not affected by the anti-SARS-CoV-2 Pfizer–BioNtech mRNA vaccine, in particular the three-dose regimen.

Introduction

Since the emergence of the mRNA vaccines against SARS-CoV-2 infection, broad concerns regarding their effect on male and female future fertility have persisted. Social media publications continue to cause hesitation regarding vaccination of the young population, even though no reproductive adverse effects were proven in clinical trials. Among anti-SARS-CoV-2 vaccine trial participants, rates of unintended pregnancies were similar in vaccinated and nonvaccinated groups, with no difference in miscarriage rates.¹ Several cohort studies demonstrated no effect of vaccination on artificial reproductive technology (ART) outcomes either in frozen embryo transfers² or in ovarian stimulation cycles.³

Our group demonstrated that recent vaccination with the Pfizer–BioNtech mRNA vaccine did not alter follicular function during ART.⁴ Semen analysis studies showed no negative effects on sperm parameters after receiving the common two-dose regimen of mRNA vaccines.^5,6 Hence, the clinical data currently support the initial finding that there is no harmful effect on fertility as a result of anti-COVID-19 vaccination.

Nationwide anti-COVID-19 vaccination began in Israel in December 2020, employing the Pfizer–BioNtech vaccine (BNT162b2 mRNA; BioNTech SE, Rhineland-Palatinate, Germany). During July 2021, Israeli citizens began receiving a boosting vaccine dose, starting with high-risk patients and later available for all citizens above 12 years of age and at least 5 months after the second vaccine dose. By the end of our study period (November 24, 2021), 6,292,211 patients had received their first vaccine, 5,776,797 received their second dose, and 4,064,932 had received the boosting vaccine dose. These numbers represent 67.66%, 62.12%, and 43.71% of the total population of Israel, respectively.

Clinical data regarding the booster vaccine dose and its impact on female and male fertility are lacking. In the absence of reliable information, fake news and faulty reasoning may compromise vaccination efforts. This is particularly important in the context of fertility patients, since completing the vaccination regimen is recommended before pregnancy.

In this study, we aimed to assess whether the Pfizer–BioNtech mRNA vaccine boosting dose produced an effect on reproductive outcomes in ART.

Materials and Methods

The study was approved by the Hadassah Medical Center IRB (Permit 0594-21-HMO).

Study population and design

We performed a prospective observational study, including 157 consecutive cycles carried out in a single university-affiliated in-vitro fertilization (IVF) unit. All patients undergoing an ART procedure between October 1, 2021, and November 24, 2021, were eligible for inclusion; patients who were unable to provide the dates for the relevant events were excluded. Female patients who were both vaccinated and convalescent were excluded as well. Male patients were included only in cases of a fertilization cycle utilizing a fresh sperm sample.

The study time period included a window between the pandemic waves, starting at the fading phase of the Delta variant outbreak and ending just before the emergence of the Omicron variant in Israel. This enabled us to assess the vaccine exposure without coexposure of a new strain, which would involve cancelation of treatments and a mixed effect.

In Israel, the entire population is covered by the public health system, therefore, vaccination was available for all patients upon consent. Patients were questioned before the scheduled ART procedure regarding their vaccination status or SARS-CoV-2 infection history, and asked to provide dates for each option. When the date was provided by month and year, but not by day, the 15th day of the specified month was used as the reference date.

The study population was divided into four groups according to their exposure status: vaccinated patients who received a boosting vaccine dose (three total doses), vaccinated patients who were vaccinated without the booster dose (one or two vaccine doses), PCR-confirmed COVID-19 convalescent patients, and unexposed patients (i.e., those who declined vaccination and had no history of COVID-19 disease).

The following demographic and clinical information was retrieved and assembled into the database: age at oocyte retrieval, ART indication, sperm source (partner/donor), ovarian stimulation results, and fertilization and pregnancy rates. In cases of a fertilization cycle involving a fresh sperm sample of a male partner, the concentration and motility on oocyte retrieval day were compared with the basal sperm analysis upon admission. Pregnancy was defined as a positive beta Human chorionic gonadotropin (bHCG) result 12–14 days after embryo transfer (<5 IU/L). Clinical pregnancy was defined as a visible gestational sac on transvaginal ultrasound, at least 7 days after a positive bHCG result. The primary outcome measure was clinical pregnancy rate. Secondary measures were ovarian response parameters and sperm parameters.

Statistical analysis

All analyses were performed using SPSS 27.0 (SPSS, Inc., Chicago, IL). Continuous intervals and ratios that were not normally distributed were transformed by square root or logarithmic scale for normality correction. Normally distributed continuous variables were compared across study groups by ANOVA. Rates and proportions were compared with the chi-square or Fisher's exact tests as appropriate in case of small numbers. All p-values were tested as two tailed and considered significant at <0.05.

Results

Outcomes among female patients

During the study period, there were 137 ovarian stimulation cycles in our IVF unit, and 96 frozen thawed embryo cycles. In total, 30 patients were excluded from the study results since they were both vaccinated and convalescent, and 46 were excluded due to lack of knowledge regarding their vaccination timing.

The study cohort included 157 consecutive cycles: 130 fertilization cycles (82.8%) and 27 oocyte cryopreservation cycles (17.2%). Female patients ranged in age from 20 to 47 years; 32 (20.4%) were undergoing ART for male infertility, 75 (47.8%) for female or unexplained infertility, and 50 (31.8%) for noninfertility indications (preimplantation genetic testing, fertility preservation, and oocyte donation embryo transfer).

Vaccination and convalescent status among the female study population were distributed as follows: 99 (63%) vaccinated and boosted, 24 (15.3%) were vaccinated without the booster dose (22 patients with two doses and 2 patients with one dose), 21 (13.4%) convalescent, and 13 (8.3%) patients were unexposed. ART indication and ART treatment type did not significantly differ between the study groups, but convalescent patients were significantly younger (Table 1).

Table 1.

Artificial Reproductive Technology Characteristics Among Study Groups (Entire Cohort)

	Total, N = 157	Vaccinated with boosting dose, N = 99	Not vaccinated, N = 13	Vaccinated without boosting dose, N = 24	Convalescent, N = 21	p
Age at oocyte retrieval	33.42 ± 6.0	34.23 ± 5.9	34.75 ± 5.6	32.43 ± 7.5	29.9 ± 5.6	0.026^{^*}
ART indication
Male factor	32 (20.4%)	18 (18.2%)	1 (7.7%)	6 (25.0%)	7 (33.3%)	0.41
Female+unexplained	75 (47.8%)	45 (45.5%)	8 (61.5%)	13 (54.2%)	9 (42.9%)
No infertility	50 (31.8%)	36 (36.4%)	4 (30.8%)	5 (20.8%)	5 (23.8%)
ART treatment type
Ovarian stimulation and fertilization	58 (36.9%)	41 (41.4%)	3 (23.1%)	8 (33.3%)	6 (28.6%)	0.79
Thawed embryo transfer	72 (45.9%)	41 (41.4%)	8 (61.5%)	12 (50.0%)	11 (52.4%)
Oocyte cryopreservation	27 (17.2%)	17 (17.2%)	2 (15.4%)	4 (16.7%)	4 (19.0%)

The bold column represents the boosting dose group, for easier orientation.

p value < 0.05.

ART, artificial reproductive technology.

Vaccinated patients who received a boosting vaccine dose were treated within 43.3 ± 30.9 days of receipt of the last dose, whereas patients who were vaccinated without the boosting dose or convalescent were treated 168.7 ± 53 and 209.6 ± 85.1 days after their last exposure (to virus or vaccine), respectively.

There were 97 embryo transfers, among them 30 (30.9%) were fresh cycles and 67 (69.1%) were thawed embryo cycles. Clinical pregnancy rate did not differ between the study groups despite age differences (Table 2) (p = 0.78).

Table 2.

Embryo Transfer Data and Pregnancy Rate by Study Group

	Total, N = 97	Vaccinated with boosting dose, N = 58	Not vaccinated, N = 9	Vaccinated without boosting dose, N = 17	Convalescent, N = 13	p
Age at oocyte retrieval	33.1 ± 6.7	34.5 ± 6.4	34.3 ± 4.9	31.3 ± 7.8	28.4 ± 4.1	0.018^{^*}
Thawed embryo cycle, n (%)	67 (69.1%)	38 (65.5%)	6 (66.7%)	12 (70.6%)	11 (84.6%)	0.60
Endometrial lining (mm)	9.3 ± 1.8	9.4 ± 2.0	9.5 ± 1.1	9.2 ± 1.6	9.2 ± 1.9	0.97
Double embryo transfer	29 (29.9%)	16 (27.6%)	4 (44.4%)	7 (41.2%)	2 (15.4%)	0.34
Pregnancy rate	43 (44.3%)	24 (41.4%)	5 (55.6%)	7 (41.2%)	7 (53.8%)	0.75
Clinical pregnancy rate	33 (34.0%)	19 (32.8%)	2 (22.2%)	7 (41.2%)	5 (38.5%)	0.78

The bold column represents the boosting dose group, for easier orientation.

p value < 0.05.

Ovarian stimulation parameters were compared among stimulated patients (N = 85) (Table 3). Vaccination or virus exposure status did not impact treatment outcomes; specifically maximal estradiol levels and number of oocytes retrieved (p = 0.50, 0.97 respectively) (Table 3). Although endometrial thickness was found to differ statistically significantly within the exposure groups (p = 0.04), this finding does not seem to bear any clinical relevance, due to sufficient thickness. Fertilization rates in intracytoplasmic sperm injection and using insemination were distributed equally among the study groups (p = 0.60, 0.96 respectively).

Table 3.

In-Vitro Fertilization Cycle Parameters by Study Group (Ovarian Stimulation Cycles)

	Total, N = 85	Vaccinated with boosting dose, N = 58	Not vaccinated, N = 5	Vaccinated without boosting dose, N = 12	Convalescent, N = 10	p
Age at oocyte retrieval	34.81 ± 5.7	34.79 ± 5.3	37.0 ± 4.0	37.08 ± 6.11	33.1 ± 6.8	0.07
AFC	15.88 ± 5.9	15.75 ± 6.2	14.0 ± 2.6	14.9 ± 7.4	17.85 ± 3.1	0.55
Induction days	9.64 ± 2.2	9.5 ± 2.2	9.0 ± 1.4	10.3 ± 1.8	10.10 ± 3.1	0.50
Total FSH units	2773 ± 1307	2685 ± 1335	2902 ± 1125	3257 ± 858	2638 ± 1670	0.28
Maximal E2 levels (pmol/L)	10119.31 ± 6857	10930.72 ± 7133	8311.40 ± 2857	8458.25 ± 7471	8310.30 ± 5610	0.50
Endometrial lining (mm)	10.1 ± 2.1	10.1 ± 2.1	8.8 ± 1.2	9.1 ± 1.8	11.4 ± 2.0	0.04^{^*}
Retrieved oocytes	11.9 ± 8.8	12.0 ± 8.8	10.2 ± 7.2	12 ± 10.9	11.8 ± 7.9	0.97
Fertilization rate
Insemination (N = 15)	0.41 ± 0.3	0.41 ± 0.3	0.36 ± 0	0.47 ± 0.3	0.32 ± 0.02	0.96
ICSI (N = 51)	0.69 ± 0.2	0.68 ± 0.2	0.67 ± 0.3	0.67 ± 0.4	0.84 ± 0.2	0.60
Top quality embryos	4.09 ± 4.7	4.38 ± 5.3	4 ± 2.6	2.25 ± 2.7	4.8 ± 2.8	0.34

The bold column represents the boosting dose group, for easier orientation.

p value < 0.05.

AFC, antral follicle count; FSH, follicle stimulating hormone; ICSI, intracytoplasmic sperm injection.

Outcomes among male patients

Male parameters were compared between procedure and baseline, only if a fresh nondonor sample was provided (N = 46). Although baseline values differed in terms of time elapsed since exposure to disease or vaccination, all baseline values were obtained before the third vaccine dose. Sperm parameters for the entire cohort did not differ significantly when comparing baseline and procedure-day results (p > 0.5 for concentration and motility parameters). Among male partners, 22 of 46 (47.8%) had received a third vaccine dose and 17 of 46 (37%) were treated due to a male factor diagnosis.

We stratified the cohort according to the third vaccine dose: sperm concentration and motility were not significantly different after the vaccine (p = 0.49 and 0.49, respectively). A stratification according to male factor infertility and vaccination status resulted in small samples: seven male partners diagnosed for male factor infertility received the third dose versus eight male partners with male factor infertility who were convalescent and/or received fewer than three doses. The small groups limited the analysis but did not demonstrate a significant difference—neither clinical nor statistical.

Discussion

Since mRNA vaccines against COVID-19 became globally available in December 2020, there has been public concern regarding their safety in men and women of reproductive age. To the best of our knowledge, our study is the first to evaluate fertility outcomes in ART-treated patients who were exposed to the three-dose regimen. We found similar clinical pregnancy rates among vaccinated groups and comparable ovarian stimulation parameters in vaccinated boosted patients, vaccinated without the booster dose, convalescent patients, or nonexposed patients.

In terms of semen parameters, vaccination had no effect on sperm concentration or motility. These results further support the observation that the Pfizer–BioNtech vaccine is not associated with adverse reproductive effects and is not potentially deleterious to fertility.

Previous studies demonstrated similar results in the context of the two-dose regimen.^2
–4 Lifshitz et al. tested sperm parameters within 1–2 months receipt of a second dose of Pfizer–BioNTech anti-COVID-19 vaccine in healthy fertile males: no significant differences in sperm parameters were noted.⁶ Similarly, Gonzalez et al. reported no differences in sperm parameters among a cohort of healthy males after two doses of an anti-COVID-19 mRNA vaccine.⁵ Changes in anti-Müllerian hormone (AMH) levels before and after vaccinations were also assessed: Mohr-Sasson et al. followed 129 reproductive-age women who received two doses of mRNA vaccinations and reported that AMH levels before and after vaccinations did not demonstrate a significant difference.

In addition, no association was found between the degree of immune response and AMH levels.⁷ Among infertile female patients, anti-COVID-19 mRNA vaccine was not shown to impact ovarian function and was not shown to have a detrimental effect on function of the ovarian follicle or IVF cycle performance.⁴ Our results provide further reassurance regarding long-term reproductive effects of the mRNA vaccine, since patients in the present cohort who received the two-dose regimen only were followed up for a longer period than in the previous studies.

Several animal studies demonstrated improved fertility postvaccination against different organisms, through an unknown mechanism.^8,9 In humans, Human Papilloma Virus (HPV) vaccine was not associated with self-reported infertility.¹⁰ Another study found that HPV vaccination was positively associated with increased fecundability, especially in patients with a history of sexually transmitted infections. This effect can be attributed to the protection from HPV infection, which can impair fertility.¹¹ A similar explanation may be reasonable for the improved fertility observed in animal studies, however, the available data are inconclusive.

Our results did not demonstrate improved fertility postvaccination, although similar pregnancy rates in older patients may support a beneficial effect. Nevertheless, receiving the third boosting dose was not harmful regarding reproductive results in relation to the two-dose regimen. This outcome together with previous studies reassures safety of mRNA vaccines in reproductive-age male and female patients.

This study is limited by its small sample size, hence future additional studies are required for further support of our results. Since we wished to avoid a confounding effect of recent COVID-19 infection, we limited the study so that it ended as soon as the Omicron variant outbreak emerged. This limitation led to small study group populations. Therefore, the male partner study group was too small to enable statistical subgroup analysis and to explore possible subpopulation differential effect. Furthermore, we did not perform concordance tests between partners. Lastly, we could not perform a comparison between patients who were partially vaccinated because only two patients were vaccinated once.

Our strengths include follow-up of a full cohort and does present, for the first time, postboosting dose performance of IVF patients in terms of response and pregnancy. Our ability to perform such a study is enabled by a public health system covering both vaccine and IVF treatment.

Conclusions

Our present study provides further reassurance that IVF outcomes are not negatively affected after the Pfizer–BioNtech mRNA vaccine, in particular for the three-dose regimen. Although it includes a small sample size, the preliminary results are reassuring. We expect that our results together with future studies will enhance our knowledge regarding vaccination safety. By providing evidence-based data, practitioners of reproductive medicine may promote the health and well-being of their patients.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for performance of this study.

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