Neutralizing antibodies are critical in the fight against COVID-19 because they defend cells from infection by the virus. A virus typically produces an immune response of many antibodies that act as an army to help fight off the virus; however, only a small subset of those antibodies are capable of neutralization—blocking the virus from infecting additional cells. Those neutralizing antibodies develop either in response to natural infection or to vaccination, then subsequently bind to the virus and block infection.
Validation trials of Covishield and the Pfizer vaccine trials have used COVID New Ab test as a marker to measure immunogenecity.
In Oxford vaccine trials the primary end point was appearance or avoidance of severe COVID symptoms confirmed by RT-PCR and not antibody testing or humoral immunogenecity. There was no secondary end point of antibody response.