Vaccination efforts against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the culprit behind the coronavirus disease (COVID-19) pandemic, have commenced in most countries. SARS-CoV-2 genetic sequence data was shared through GISAID on 10 January 2020, and on 19 March, the global pharmaceutical industry announced a major commitment to address COVID-19.
Currently, 18 vaccines are approved by a national regulatory authority for use by the public as of June 2021. As a result of the SARS-CoV-2 vaccines, the spread, severity, and death due to COVID-19 have significantly been reduced. Phase III trials have shown that several COVID-19 vaccines reduce symptomatic SARS-CoV-2 infections by as much as 95%.
Some of the vaccines include new messenger RNA (mRNA) vaccines like the BNT162b2 mRNA COVID-19 vaccine, also known as the Pfizer-BioNTech vaccine. The BNT162b2 vaccine induces spike protein-specific neutralizing antibodies tied to protective immunity.
Researchers at the Institute of Biomedicine, the University of Turku in Finland showed that the blood of BNT162b2-vaccinated health care workers effectively neutralized the SARS-CoV-2 variant with the D614G substitution and the B.1.1.7 variant (Alpha variant) after the second dose.
The study, which was published in the journal Nature Communications, demonstrated that the neutralization of the B.1.351 variant or the Beta variant has been reduced five-fold. However, despite the decrease, 92 percent of the seronegative vaccinees have a neutralization titer of more than 20 for the B.1.351 variant, showing some protection.
Currently, many countries are vaccinating residents against SARS-CoV-2. To date, more than 3 billion doses of COVID-19 vaccines have been administered globally.
SARS-CoV-2 vaccines target the spike protein (S), which binds and invades healthy host cells. Currently, two messenger RNA (mRNA) vaccines (BNT162b2 and mRNA-1273) and two adenoviral vector-based vaccines (ChAdOx1-S by AstraZeneca-Oxford and COVID-19 Vaccine Janssen by Janssen Biologics B.V. and Janssen Pharmaceutica NV) are approved by the European Medicines Agency (EMA) for use in Europe.
The vaccines are designed to produce spike protein-specific antibodies and induce anti-S immunoglobulin G (IgG) with neutralizing activity against the first pandemic SARS-CoV-2 Wuhan Hu-1 variant and the currently circulating D614G variants.
However, the recent emergence of new variants of concern, including the B.1.1.7 or Alpha variant in the United Kingdom and the B.1.351 variant or the Beta variant that was first reported in South Africa, has raised concerns about increased infectivity and reduced vaccine efficacy. Also, these variants are characterized by eight to ten protein changes in the S protein, where vaccine-induced antibodies are targeted.
BNT162b2 vaccine-induced antibody responses
To arrive at the study findings, the researchers characterized the BNT162b2 vaccine-induced antibody responses in the sera of 180 Finnish healthcare workers who received two doses of COVID-19 vaccine with three weeks intervals.
From there, they checked for SARS-CoV-2 S1-specific IgG, Immunoglobulin A (IgA), and the immunoglobulin M (IgM) antibody responses and neutralization titers for three SARS-CoV-2 variants, namely the D614G, B.1.1.7, and the B.1.351 variants.
The team revealed that receiving a two-dose vaccination yields high levels of anti-S1 IgG antibodies in 100 percent of the vaccinees. Further, the team noted that the second vaccine dose induces antibodies for efficient neutralization of the D614G and the B.1.1.7, while the titers for the B.1.351 variant were lower.
“The study showed that the Pfizer-BioNTech BNT162b2 COVID-19 mRNA vaccine is highly immunogenic, and particularly after two vaccine doses, all vaccinees showed a very high humoral immune response to D614G variant viruses,” the researchers noted in the study.
“All vaccines that have currently obtained market authorization in the E.U. show excellent protective efficacy against severe COVID-19. Thus, it is very likely that immunogenicity results similar to those presented here will be applicable to them as well,” they added.
The team recommends that future studies should tackle the development and persistence of cell-mediated immunity. As more people become vaccinated, the team plans to systemically collect serum and cellular samples to compare analyses about vaccine-induced immunity, the longevity of vaccine, natural infection-induced immunity, and cross-protection.