Covishield vaccine induces immunity for at least one year following a single dose

Strong immune responses following either a late second dose or a third dose

by Emme Haddon

In early March 2021, I received my first shot of Covishield but began to get a little worried when the recommended three-month time frame had passed for the second dose with no sign of the promised shipment from India. Finally, in the first week of August, some months later, after what seemed like an interminable wait, I was fortunate enough to secure my second dose of Covishield, along with 490,000 or so others.

The findings of a study of Vaxzevria, the European brand name for the UK’s AstraZeneca vaccine of which the Indian-manufactured Covishield is biologically identical, from the Oxford-led COV001 and COV002 trials by researchers at the University of Oxford, released on June 28, 2021 on the pre-preprint server of the Lancet, demonstrated that antibody levels remain elevated from baseline for at least one year following a single dose.

Furthermore, a 45-week dosing interval between the first and second dose of Covishield, resulted in an 18-fold increase in antibody response, measured 28 days after the second dose. Antibody titers (test determining level of antibodiess in the blood) were four times higher than with a 12-week interval, demonstrating that a longer dosing interval is not detrimental but can derive stronger immunity. The analysis included volunteers aged 18 to 55 years who were enrolled in COV001 and COV002 trials and had received either a single dose or two doses of COVID-19 Vaccine AstraZeneca.

In addition, a third dose of Vaxzevria given at least sixmonths after a second dose, boosted antibody levels sixfold, maintained T cell response and also resulted in higher neutralising activity against the Alpha (B.1.1.7, ‘Kent’), Beta (B.1.351, ‘South African’) and Delta (B.1.617.2, ‘Indian’) variants. Both the late second dose and the third dose of Vaxzevria were less reactogenic than the first dose.

It seems that those of us who patiently endured a five-month wait for their second dose of Covishield, may in fact, be better protected than those who, by whatever means they felt necessary, managed to secure their second dose in the previously recommended three-month dosing interval, before supplies ran out. As the old adage goes: good things come to those who wait springs to mind!

The release of the findings of a second study on July 28. 2021, by researchers from the University of Oxford, concluded that the risk of the rare blood clotting thrombocytopenia, venous thromboembolism and arterial thromboembolism after receiving first doses of AstraZeneca or Pfizer COVID-19 jabs is far lower than from the actual virus.

Rates of venous thromboembolism were eight times higher after a diagnosis of COVID-19 infection compared with the expected rate. Many developed countries limited AstraZeneca’s use to older adults because of concerns about an elevated risk of blood clots affecting the younger population. These findings should allay any fears about the vaccine’s safety.

Results from the Canadian Immunization Research Network with support from the Public Health Agency of Canada and the Canadian Institutes of Health Research, published as a pre-print on July 23, 2021, showed that one dose of Vaxzevria (Covishield) was 82% effective against Beta/Gamma and 87% and 90 % effective against the Delta (B.617.2, ‘Indian’) and Alpha (B.1.1.7, ‘Kent’) variants’ hospitalisation or death.

Research into the coronavirus is on-going and it important to ensure that officials keep abreast of new developments and plan accordingly. In countries such as Sri Lanka with limited resources, hard hit economically by Covid-19, where the majority of those under the age of 30 have yet to receive a first vaccine, the findings that Covishield’s antibody levels remain elevated from baseline for at least one year following a single dose, with increased immunity provided as a result of a longer dosing interval are potentially game-changing.

The Delta virus variant has changed the shape of the pandemic. At a time when the vaccination program is struggling to keep up with rapid transmission of the Delta variant, any Covishield vaccines kept aside for second doses, might be better utilised now as first doses to prevent hospitalizations and deaths in those higher risk as yet unvaccinated groups.