Newly released Pfizer document - Vaccination Effects on Fertility in Rats from 2020

Important study

Superb Timing

I was looking for some information from one of the Pfizer documents when I came across this one. It was released in the latest November tranche of documents and is a Combined Fertility and Developmental Study (Including Teratogenicity and Postnatal Investigations) of BNT162b1, BNT162b2 and BNT162b3 by Intramuscular Administration in the Wistar Rat. The Pfizer vaccine that was approved for emergency use was BNT162b2.

Remember, these were the documents that were only released after a Court ruled the FDA should do so and therefore it was always likely the worst documents would be released last.

Photo by Kalyan Sak on Unsplash

This document was approved on 22 December 2020. In April 2021, the UK issued new advice that pregnant women should be offered the COVID-19 vaccine at the same time as the rest of the population, based on their age and clinical group.

The study was undertaken by Charles River, an American pharmaceutical company specialising in a variety of pre-clinical and clinical laboratory services for the pharmaceutical, medical device and biotechnology industries. That description was taken from their 2019 Wikipedia page.

Their current Wikipedia page now includes specialising in gene and cell therapy. In what one might consider impeccable timing, their new specialisation came about through the acquisition of California based HemaCare, which was announced in December 2019.

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Abstract & Conclusion

The objective of the study was to assess potential effects of the vaccine candidates and the immune response, on fertility and pre and postnatal development in the female Wistar rat.

The vaccines were administered intramuscularly to Female Wistar rates 21 and 14 days before mating and then on gestation day 9 and 20 (4 doses in total). The control group had a saline solution on the same days and under the same conditions. Each group had 44 females, 22 which were assigned to the caesarean subgroup and 22 to the littering subgroup.

After mating with unvaccinated males (so we have no idea if there are any fertility issues with males), 22 rats underwent caesarean section on day 21, whilst the rest were allowed to litter and offspring observed up to weaning on postnatal day 21.

So let’s skip straight to the conclusion as most people might do.

Intramuscular administration of BNT162b1, BNT162b2 and BNT162b3 before and during gestation to female Wistar (CRL:WI[Han]) rats was associated with non-adverse effects (body weight, food consumption and effects localized to the injection site) after each dose administration. There were no effects of any of the 3 vaccine candidates on mating performance or fertility in F0 female rats or on embryo-fetal or postnatal survival, growth, or development of the F1 offspring. An immune response was confirmed in F0 female rats following administration of each vaccine candidate and these responses were also detectable in the F1 offspring (fetuses and pups).

Only non-adverse effects and no effects on mating performance or fertility. Furthermore, no effects on embryo-fetal or postnatal survival, growth or development of the offspring. However, an immune response was detectable in the F1 offspring, so clearly something is being transferred to the pups.

All sounds promising - quick get every pregnant woman vaccinated - it has been tested on 44 rats after all. However, a closer look at the body of the report raises some concerns.

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Main report

Unscheduled deaths

Although the report states that there were no deaths throughout the study related to any of the 3 vaccine candidates, later in the text it says there were three unscheduled deaths in the female rates.

A moribund female showing signs of parturition difficulties and 2 females with total litter death were euthanized by carbon dioxide inhalation and exsanguination.

Mortality

Further down the report it contradicts itself again and says there was no unscheduled death related to any of the 3 vaccine candidates.

However it notes that one female from the BNT162b3 group had parturition difficulties and was euthanised for ethical reasons.

The female delivered 8 pups. On LD0, distended/blue abdomen was noted. On LD1, hunched posture, pale, marked piloerection, bleeding at the vulva/red vaginal discharge, distended/purple abdomen were noted and 4 of the delivered pups were missing/dead/cannibalized. At necropsy, the female had 13 implantations, 3 fetuses were retained in the uterus. No macroscopic findings were noted.

The authors say that such cases of parturition difficulties are present in historical control data (a study in 2016) for this strain of rat so these finding were considered to be incidental.

One female in the BNT162b1 group incurred total litter death of 15 pups (9 stillborn, 3 cannibalised, 1 dead and 2 missing pups). Another female from the BNT162b3 group delivered 8 stillborn pups.

Again, the authors say total litter death at or shortly after birth is present in historical data (two studies out of 18 between 2015 and 2019) so they conclude the deaths were incidental and not related to the vaccines.

Clinical Observations

Apparently there were no adverse clinical signs because again they were considered incidental.

Other clinical signs such as abnormal vocalization, chromodacryorrhea, desquamation, erythema, localized hairloss, malocclusion, long or missing teeth, red vaginal discharge, red stained fur, scab(s), sore(s) noted sporadically across the groups were considered to be incidental, related to the method of dose administration or to the pregnancy status of the females.

Body Weight

Mean body weight gain was lower in the BNT162b1 and BNT162b3 groups (26 g and 30 g), compared with the control group (33 g) throughout the lactation phase. This was not considered vaccine-related, but due to an atypical high value in the control group compared with the historical control data range (from 10.9 g to 32.6 g).

Food Consumption

Reduced mean food consumption was noted after the first 3 dose administrations (M-21, M-14 and GD9) in the BNT162b1, BNT162b2 and BNT162b3 groups compared with the control group (up to -14, -16 and -17% on GD9, respectively). Complete recovery was noted between each of the dose administrations such that mean food consumption was comparable with the control group during the premating and gestation periods, therefore none of the transient differences from control were considered adverse.

Pre-Implantation Data

The mean percentage pre-implantation loss was higher in the BNT162b2 and BNT162b3 groups (9.77% and 7.96%, respectively) compared with the control group (4.09%). However, the differences were not biologically meaningful and the values remained within the historical control data range (5.1% to 11.5%) for pivotal studies, so the difference was considered to be incidental.

External Observations

From the BNT162b1 group, Fetus 17 (F35) had exencephaly, open eye and spina bifida in the cervical region. Exencephaly and open eye are part of the background data for this strain of rat. These malformations noted for a single fetus were therefore considered incidental in view of the isolated incidence.

In the BNT162b2 group, there was Fetus 14 (F58) had gastroschisis and Fetus 14 (F64) had a small mouth and agnathia. These malformations are part of the background data for this strain of rat (CRL:WI(Han)) and were considered incidental in view of their isolated and sporadic nature

Visceral Observations

Again, the report states there were no effects on fetal soft tissue morphology due to the vaccines.

However, from the BNT162b1 group, one fetus has narrowed ductus arteriosus and another had a retinal fold. One fetus in the BNT162b2 group has a right-sided aortic arch and one from the BNT162b3 group has a ventricular septum defect. These were, again, all considered incidental, as were less severe soft tissue anomalies.

Skeletal Observations

No effects on fetal skeletal morphology were reported but in the BNT162b1 group a fetus had acrania and multiple abnormalities of thoracic and cervical vertebrae. In the BNT162b2 group a fetus had short and fused mandibles. All of these, including other less severe anomalies, such as supernumerary lumbar ribs, 7 lumbar vertebrae or incomplete ossification of thoracic centrum, were considered incidental.

Pre-Birth Loss

No effect on pre-birth loss reported. However, in the BNT162b1 group pre-birth loss was 12.2% and in the BNT162b3 group it was 13.8%. This compared with the control group at 6.8% but was within historical ranges so considered incidental.

Consequently, the mean number of pups delivered was marginally lower in the BNT162b1 and BNT162b3 groups (11.9 and 11.4, respectively) compared with the control group (13.3). However, the values remained consistent with the historical control data range (from 9.9 to 11.8) for pivotal studies.

Pup Viability and Litter Sizes

No effects were observed which were related to the vaccines. However, in the BNT162b1 group the live birth rate was 93.2% and in BNT162b3 it was 94.7%, compared with 98% in the control group.

Consequently, the mean live litter size was marginally lower in the BNT162b1 and BNT162b3 groups (11.0 and 11.3, respectively) compared with concurrent control group (13.0). However, the values were consistent with the background data for this strain of rat (from 9.8 to 11.6)

Necropsy finding of adult females

Abnormalities of the liver (diaphragmatic hernia, mottled surface, abnormal shape or adherent mass) were occasionally noted for isolated females across all groups (including controls) and were considered incidental.

It seems all of the adverse events above were considered incidental by the authors but I guess they are in a much better position to analyse the data. Furthermore, many of the adverse events related to the other two vaccine candidates, it was BNT162b2 which was eventually selected for emergency use authorisation.

However, with so many adverse events only happening in the vaccine groups I would want to study the effects on more than 44 rats before advising every pregnant woman in the world to get injected.

This article just looked at the first 40 pages out of 1145 but flicking through the rest there is a lot more to report on. I will do so over the next few days so please subscribe to get the latest articles in your inbox.