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Covid jab study of 99m people links shots to rare risk of disorders

Covid vaccines have been linked to small increases in heart, blood and neurological disorders, according to the largest global study of its kind, in which an international coalition of vaccine experts looked for 13 medical conditions among 99m recipients across eight countries.

The goal was to identify higher rates of those conditions after people had received the shots, according to the findings in the journal Vaccine, and while the scientists linked some of the jabs to higher risk of several conditions, the absolute risk of developing these was small. For instance, they said, the benefits of vaccination far outweighed the risks for any neurological issues.

However, their findings suggest that the PfizerModerna and AstraZeneca vaccines are linked to significantly higher risk of five specific conditions – including a nerve-wasting condition that leaves people struggling to walk or think – and warned of several other disorders warranting further investigation, as well as the links between a brain-swelling condition and Moderna’s shot.

But, they said, the risk of developing any one of the conditions was minimal, reports Daily Mail.

For instance, of the total 13bn doses of vaccines administered, there have only been 2 000 cases of all conditions.

Dr Harlan Krumholz, director of the Yale New Haven Hospital Centre for Outcomes Research and Evaluation and a lead investigator in the study, said: “Both things can be true.

“Vaccines can save millions of lives, and there can be a small number of people who’ve been adversely affected.”

Covid vaccines are estimated to have averted more than 19m deaths worldwide, including 3m in the US alone.

Among the team’s discoveries was a two-fold increase in the risk of the neurological autoimmune condition Guillain-Barre Syndrome.

The report said that of the 23m AstraZeneca shots administered worldwide, they would have expected 76 cases of GBS – but 190 events were observed, accounting for a 2.9-fold increased risk.

While it cannot be proven that the vaccine caused these events, there is some evidence it triggers the immune system to attack its own nerves.

Meanwhile, the study also confirmed a three-fold higher risk for the heart inflammation condition myocarditis, though researchers did not give the number of expected cases versus actual cases.

Myocarditis was seen most commonly in young men. It’s believed to be related to immune response triggered by the mRNA vaccines by Pfizer and Moderna, which work by instructing cells to produce the same protein that sits atop the coronavirus.

This prompts the immune system to produce antibodies against the spike protein, providing protection against Covid. In rare cases, this immune response may lead to inflammation in the heart muscle.

Typically, the myocarditis instances have been relatively mild, leading to just 28 deaths.

Additionally, both the first and fourth doses of the Moderna vaccine had between 1.7 and 2.6 times a greater number of instances of pericarditis, the inflammation affecting the protective sac encasing the heart.

The teams looked at more than 39m Moderna vaccine doses administered.

Like the link between myocarditis and the vaccines, links to pericarditis are still under investigation. It is believed to be caused by the same mechanism, an overactive immune response that attacks the thin sac-like membrane.

There was a greater than 3.7 times risk of a condition called Acute Disseminated Encephalomyelitis (ADEM), which causes swelling in the brain and spinal cord that damages the protective covering of nerve fibres in both after the first dose of the Moderna vaccine.

Seven instances of ADEM occurred after vaccination with the Pfizer-BioNTech vaccine, surpassing the anticipated count of two cases.

There were nearly 190m shots considered in the study.

The study also found that after getting the first dose of the AstraZeneca vaccine, there were 1.9 and 3.9 times increased risks of transverse myelitis and ADEM, respectively.

Bell’s palsy, which causes temporary weakness or paralysis of the muscles on one side of the face, had an increased odds of 1.05 after a first dose of the Pfizer vaccine.

There was also a 1.3 to 1.4 times greater risk of having a seizure after the first and second doses of the Moderna vaccine, as well as the fourth dose of the Pfizer vaccine.

The researchers added a major caveat to this finding: “Chances of having a neurological event after acute SARS-CoV-2 infection were up to 617-fold higher than after Covid vaccination, suggesting that the benefits of vaccination substantially outweigh the risks.”

After a first dose of the AstraZeneca vaccine, there was a 3.2-times-greater than expected risk of Cerebral Venous Sinus Thrombosis (CVST).

The risks after the first dose of the Pfizer vaccine and after the second dose were 1.49 and 1.25 times higher.

CVST is a rare but serious condition characterised by the formation of blood clots in the large channels that drain blood from the brain and deliver it back to the heart after the AstraZeneca vaccine.

In total, 21 events were expected, while 69 events were observed.

Also after the first dose of the AstraZeneca vaccine, there was a 1.07 times higher risk of thrombocytopenia, a condition characterised by a lower-than-normal number of platelets in the blood.

After a third dose of ChAdOx1, the risk notably rose to 1.95.

Study details

Covid-19 vaccines and adverse events of special interest: A multinational Global Vaccine Data Network (GVDN) cohort study of 99 million vaccinated individuals

K. Faksova, D. Walsh, Y. Jiang, J. Griffin, et al.

Published in Vaccine on 12 February 2024


The Global Covid Vaccine Safety (GCoVS) Project, established in 2021 under the multinational Global Vaccine Data Network™ (GVDN®), facilitates comprehensive assessment of vaccine safety. This study aimed to evaluate the risk of adverse events of special interest (AESI) following Covid-19 vaccination from 10 sites across eight countries.

Using a common protocol, this observational cohort study compared observed with expected rates of 13 selected AESI across neurological, haematological, and cardiac outcomes. Expected rates were obtained by participating sites using pre-Covid-19 vaccination healthcare data stratified by age and sex. Observed rates were reported from the same healthcare datasets since Covid-19 vaccination program rollout. AESI occurring up to 42 days following vaccination with mRNA (BNT162b2 and mRNA-1273) and adenovirus-vector (ChAdOx1) vaccines were included in the primary analysis. Risks were assessed using observed versus expected (OE) ratios with 95 % confidence intervals. Prioritised potential safety signals were those with lower bound of the 95 % confidence interval (LBCI) greater than 1.5.

Participants included 99,068,901 vaccinated individuals. In total, 183,559,462 doses of BNT162b2, 36,178,442 doses of mRNA-1273, and 23,093,399 doses of ChAdOx1 were administered across participating sites in the study period. Risk periods following homologous vaccination schedules contributed 23,168,335 person-years of follow-up. OE ratios with LBCI > 1.5 were observed for Guillain-Barré syndrome (2.49, 95 % CI: 2.15, 2.87) and cerebral venous sinus thrombosis (3.23, 95 % CI: 2.51, 4.09) following the first dose of ChAdOx1 vaccine. Acute disseminated encephalomyelitis showed an OE ratio of 3.78 (95 % CI: 1.52, 7.78) following the first dose of mRNA-1273 vaccine. The OE ratios for myocarditis and pericarditis following BNT162b2, mRNA-1273, and ChAdOx1 were significantly increased with LBCIs > 1.5.

This multi-country analysis confirmed pre-established safety signals for myocarditis, pericarditis, Guillain-Barré syndrome, and cerebral venous sinus thrombosis. Other potential safety signals that require further investigation were identified.


Vaccine article – COVID-19 vaccines and adverse events of special interest: A multinational Global Vaccine Data Network (GVDN) cohort study of 99m vaccinated individuals


Daily Mail article – Largest Covid vaccine study ever finds shots are linked to small increased risk of neurological, blood and heart disorders – but they are still extremely rare (Open access)


See more from MedicalBrief archives:


Covid jabs saved 2.4m lives in first eight months – US study


Looming legal challenges against AstraZeneca over Covid jab


Man claims R31m for Covid-19 jab ‘paralysis’


Higher myocarditis risk in young males after mRNA jabs – Nordic cohort study of 23m






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