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HÀ NỘI - Major General, Associate Professor, Dr. Nguyễn Viết Lương, of the Military Medical Academy, Ministry of National Defence - the unit participating in the trial of home-grown COVID vaccine Nanocovax, has given more details addressing concerns about the vaccine’s immunogenicity in an interview with the Vietnam News Agency.

On August 29, after a meeting to consider the application for an emergency use licence for Nanocovax by Nanogen Biopharmaceuticals, the Advisory Council for Registration of Circulation of Drugs and Medicinal Ingredients acknowledged the results submitted and appraised by the Legal Subcommittee under the National Institute for Control of Vaccines and Biologicals, the Quality Subcommittee, and by the Pharmacology and Clinical Subcommittee. It also asked the company to urgently supplement and update a number of contents of the quality dossier: safety data on pharmacological and clinical records; immunogenicity in response to new virus strains; and size of samples for immunogenicity assessment according to the research plan; the relationship between vaccine immunogenicity and protective efficacy of at least 50 per cent according to World Health Organization guidelines.

Lương explained the four important tests to evaluate the immunogenicity of Nanocovax.

Lương said that the immunogenicity (using quantitative testing of IgG antibodies to COVID-19, which shows the level of antibodies generated after infection or vaccination) of Nanocovax vaccine reached 57.56 U/ml.

Lương said that in order to compare the IgG antibody levels of vaccines, it must be done using the same unit of measurement (WHO standard unit is BAU/ml). Even to ensure the accuracy of comparison, vaccines must use the same test kit, while here the studies use different types of kits with different units of measurement.

“To evaluate the immunogenicity of the vaccine must be based on many other criteria, not only on the concentration of IgG antibodies,” Lương said.

In the Nanocovax vaccine research, the units used four tests, including a quantitative antibody test; assessment of neutralisation antibody (surrogate neutralisation antibody); assessment of neutralising antibodies on live viruses by PRNT (plaque reduction neutralisation test); and assessment of cell-mediated immunity.

Lương said that in order to standardise the data to determine the immunogenic effect of the Nanocovax vaccine, researchers could use a comparison method with the sera of people having recovered from COVID-19.

In this study, the results showed that the IgG antibody efficacy of all the serum samples studied in recovered COVID-19 patients was 5.63 U/ml on average. Meanwhile, the IgG of volunteers vaccinated with Nanocovax vaccine (with a dose of 25 mg) reached 6.77 U/ml on ​​day 35, 60.47 U/ml on day 42, and fell to 16.25 U/ml on day 90.

The significantly reduced anti-S IgG antibody levels in the vaccinated volunteers, 3.7 times compared to day 42 (from 60.47 U/ml to 16.25 U/ml) were still 2.9 times higher than that in the group of recovered COVID-19 patients (5.63 U/ml).

Lương added the published figures of the Moderna vaccine showed 5.19 times higher antibody levels in the vaccinated group at the time of peaking (day 42 after injection) compared to the group of recovered COVID-19 patients. The comparable figure for Nanocovax vaccine was 10.74 times.

As for surrogate neutralisation, the results of the study on Nanocovax also showed that the neutralisation rate of serum samples from recovered COVID-19 patients reached 5.68 per cent while that in volunteers injected with Nanocovax vaccine (with a dose of 25 mg) on ​​day 35 reached 58.39 per cent, 85.5 per cent on day 42, 72.68 per cent on day 90.

Regarding the decline in antibody levels after the peak, Lương explained normally the half-life of IgG is about 25 days, which means that for all vaccines after IgG antibody production is stimulated and peaks, the antibody levels will gradually decrease.

“That doesn't mean the vaccine loses its ability to protect. Vaccination helps the body to form specific B cells. This cell will continue to produce antibodies when antigens or viruses enter. This also shows that it is necessary to re-inject the vaccine against COVID-19 after a certain period of time," Lương.

It had been shown in research results published by Moderna regarding its emergency licensed vaccine, Lương said. With Moderna vaccine antibody concentration decreased 3.96 times on day 119 compared to day 43. By comparison, Nanocovax had a similar reduction of 3.7 times (16.25 U/ml on day 90 versus 60.47 U/ml on day 42).

Yet the antibody level on day 90 in the vaccinated group was still much higher than that in the group of recovered COVID-19 patients (16.25 U/ml versus 5.63 U/ml).

Regarding the two cases of anaphylaxis during testing he said the two incidents among 13,627 volunteers are not a large proportion compared to the claims of many other vaccines. Moreover, these were only grade 1 and grade 2 anaphylaxis, who were promptly treated, have recovered and returned to a completely normal state.

These two cases were also reported to relevant medical authorities according to regulations.

He said when the vaccine candidate had not been officially approved by the licensing council, the publication of data on research results must be agreed upon by the manufacturer and the research and evaluation agencies. This regulation is intended to protect the legitimate interests of manufacturers and agencies participating in evaluation and research as well as to ensure commitments regarding ethical issues in research.

He was concerned that false and unfounded information would not only confuse the public but also directly affect volunteers as well as producers, units, organisations and scientists participating in the research.

Lương said after reviewing the report on the results of the first two phases and phase 3a of the Nanocovax vaccine trial, the Ethics Council had made a conclusion and transferred the file to the Advisory Council to consider emergency licensing for the Nanocovax vaccine.

“The evaluations and comments of the National Ethics Council in Biomedical Research are correct, fair and objective. Currently, the company and research units have supplemented the required documents. It is hoped that the Nanocovax vaccine will be granted an emergency licence by the Advisory Council for Registration of Circulation of Drugs and Medicinal Ingredients in the first half of September 2021 so Việt Nam will have an ‘important weapon’ in the war against the pandemic, contributing to protecting people's health and soon returning life to a new normal," said Lương. -VNS