Making a difference - identifying severe side effect of Covid-19 vaccine

Severe side effect of Covid-19 vaccine

Rapid identification of the mechanism for COVID vaccine related blood clots, saved lives

Vaccination is the mainstay of controlling the global COVID-19 pandemic. The first vaccine, made by Pfizer, was rolled out in December 2020, followed by the AstraZeneca/Oxford vaccine (ChAdOx1) in January 2021.

By mid-March 2021, a rare side-effect of ChAdOx1 affecting previously fit, well young adults was identified by UCLH haematologist Professor Marie Scully and Dr Will Lester at Birmingham Hospital, now known as Vaccine-induced immune thrombocytopenia and thrombosis (VITT).

One of UCLH’s first cases was a 21-year-old man admitted with stroke and epileptic fits 12 days after his first ChAdOx1 jab in March 2021. Tests revealed thrombosis (blood clots) inside his brain and very low levels of platelets (the clotting agents in blood).

Scully and team rapidly collected and studied data on 23 similar patients who had thrombosis and low platelet counts after receiving ChAdOx11. All but two had abnormally high levels of a type of immune system protein called platelet factor 4 (PF4). Excess PF4 is usually triggered through use of a blood-thinning drug called heparin, but none of those studied had taken this drug.

The UCLH team concluded that this was a new syndrome caused by the vaccine2. The usual treatment for blood clots and low platelet counts is heparin, which would actually worsen VITT, so they realised urgent action was required.

They immediately alerted the UK regulatory authority and published their findings, in which they identified a diagnostic test and recommended treatment with immunoglobulins - immune system-dampening agents, plasma exchange and non-heparin blood thinners.

Between March and June 2021, an expert haematology group of 5 clinicians met daily to discuss new VITT cases across the UK, and liaised with colleagues worldwide to compare findings and care. In August 2021 their major review of these cases showed that VITT carries a 22% risk of death, which increased to 78% in those with poor prognostic factors. However, 90%  of this latter group survived if treated with plasma exchange, immunoglobulins and non-heparin blood thinners3.

The UK halted clinical trials using the AstraZeneca COVID-19 vaccine in children shortly after VITT was identified and the NHS stopped using the vaccine in the under-40s. In the UK there have been no new cases since July 2021, and booster vaccine roll-out has been with the Pfizer vaccine only.

References

  1. Perry et al, Lancet 2021
  2. Scully, NEJM 2021.
  3. Pavord et al, 2021