This is a summary, written by members of the CITF Secretariat, of:

Drews SJ, Hu Q, Samson R, Abe KT, Rathod B, Colwill K, Gingras AC, Yi QL, O’Brien SF. SARS-CoV-2 Virus-Like Particle Neutralizing Capacity in Blood Donors Depends on Serological Profile and Donor-Declared SARS-CoV-2 Vaccination History. Microbiol Spectr. 2022 Feb 16;10(1):e0226221. doi: 10.1128/spectrum.02262-21.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

This study, published in Microbiology Spectrum and carried out by CITF-funded researchers Drs. Steven Drews and Sheila O’Brien of Canadian Blood Services, characterized the neutralization capacity and the breadth of protection against SARS-CoV-2 and its variants of concern (Alpha, Beta, Gamma, and Delta). The authors gathered data based on the serological profile of Canadian blood donors. They found that those who were neither vaccinated nor previously infected had no pre-existing neutralizing antibodies. The highest absolute levels of neutralizing capacity were in vaccinated blood donors, further reinforcing the requirement for vaccination even in people who have been previously infected.

Samples from 4500 blood donors were stratified, first, based on donor-declared vaccination history, and then on the presence and absence of anti-N antibodies in the blood sera. In countries that are only using S antigen targeting vaccines (such as Canada), the presence of anti-N antibodies is indicative of past infection.

Key messages:

  • Anti-S and anti-RBD (receptor binding domain) values were generally higher for vaccinated donors (median – 1.6 and 1.5, respectively) compared to the unvaccinated (median – 0.46 and 0.18 respectively). This means that antibody levels generated after vaccination were higher compared to antibodies due to infection.
  • Anti-N serum signal-to-cutoff value was lower for vaccinated donors (median value of 0.05) compared to unvaccinated donors (median value of 0.39). This indicates that unvaccinated people had higher levels of anti-N antibodies generated after infection compared to vaccinated people who may have had an infection.
  • The “vaccinated and anti-N” (vaccination and prior infection) group developed neutralizing antibodies against wild-type virus-like particles () and variants of concern (VOCs) VLPs. This group had the highest absolute levels of neutralizing antibodies, with higher levels against the wild type than VOCs.
  • For the “vaccinated and no anti-N” (vaccination and no likely prior infection) group, there was a significant reduction in neutralization capacity against the VOC VLPs compared to wild-type VLPs. Neutralization of Beta was also reduced compared to Alpha and Delta VLPs.
  • For the “unvaccinated and anti-N” (prior infection only) group, there was a significant reduction in neutralization capacity of antibodies against Alpha, Beta, and Gamma compared to wild-type VLPs. Neutralization of Beta was also reduced compared to Alpha, Gamma, and Delta VLPs.
  • The “unvaccinated and no anti-N” group did not exhibit any neutralization capacity against wild-type and variant of concern VLPs.

This study is based on blood samples from people who donated to the Canadian Blood Services between January 1 and March 31, 2021. Of the donors, 54.8% were male, and the median age was 47 years. At the time of the study, only 3.1% of Canadian blood donors stated that they were vaccinated with at least one dose of a SARS-CoV-2 vaccine in the three months covered in the study. Donors were classified into four groups: vaccinated with evidence of infection-induced immunity (anti-N), vaccinated without anti-N, unvaccinated with anti-N, unvaccinated without anti-N.

Overall, this study highlighted the importance of vaccination in populations with low seroprevalence and even in those who have had a previous SARS-CoV-2 infection.