the vaccine and placebo groups respectively. the others were mild and quickly recovered. the incident of unsolicited adverse events was 0.69% in the vaccine group and 0.6% in the placebo group, including hypotension, vestibular disorders, knee pain, hand pain, hyperthyroidism, and upper respiratory tract inflammation. almost all of the unsolicited adverse events were not related to the investigational products and the majority of unsolicited (non-sae) adverse events in both vaccine and place groups were mild and moderate. there were 40 serious adverse events (saes) (including covid-19 cases) in both study groups (vaccine and placebo) in the trial, of which 36/40 saes were assessed as unrelated to the study product. four saes were assessed as possibly related by the dsmb and investigator assessments, including grade 2 anaphylactic reaction, grade 2 allergic reactions, grade 3 hypertension and exacerbation of chronic obstructive pulmonary disease (copd). all participants recovered completely. immunogenicity outcome gmc of anti-s igg binding antibody unit (bau/ml) were shown. before the 1st injection, anti-s igg level of the vaccine and placebo groups were 5.7 and 6.1 bau/ml, respectively. at day 42, anti-s igg concentration of the vaccine group reached 1254.7 bau/ml, while that of placebo group remained unchanged 5.9 bau/ml. in addition, igg response was negatively correlated with age. gmc anti-s igg of 18–45, 46-60 and above 60 groups at day 42 were 1525.8, 983.9 and 900.7 bau/ml, respectively. the correlation coefficient r was -0.2. at day 42, the gmfr of vaccine group was 218.9. meanwhile, gmfr of the placebo group was 0.96. group age of 18-45 had the highest gmfr (269.7), followed by 46-60 (166.4) and above 60 (157.9). the seroconversion rate was defined as gmfr > 4. at day 42, the seroconversion rate of vaccine group was 100%. neutralizing antibody was qualitatively and quantitatively evaluated by svnt and prnt50, respectively. svnt results were reported as the percentage (%) of participants in each group positive for the assay. at day 0, 0.6% and 3.3% participants in the vaccine and placebo groups were positive for svnt. at day 42, 96.4% in vaccine group was positive for the test but only 1.2% positive in placebo group. neutralizing antibody, assessed by prnt50, was expressed as gmt. a number of serum samples from vaccine and placebo groups at day 42 were randomly selected to assess neutralizing antibody titer on the original (wuhan) strain, the alpha variant and the delta variant. gmt of neutralizing antibody on the wuhan, alpha and delta were 57, 36.2 and 29.6, respectively. meanwhile, gmt of neutralizing antibody in placebo group was 10 (half of lower limit of detection). we found the neutralizing antibody level induced by nanocovax exceeded that of convalescent samples. type 1 and type 2 helper t cell (th1/th2) response on 77 randomly selected participants (66 in vaccine group and 11 in placebo group) were evaluated by ics for ifng and il-4 signal. il-4 signal was dominant to ifng signal at day 42, suggesting ath2 polarization induction by nanocovax. these observation was consistent with the nature of aluminum adjuvant which has been well established for th2 response induction. efficacy outcome at the data cutoff date of august 30, 2021, the vaccine efficacy was yet to be concluded due to insufficiency of confirmed positive covid-19 case. however, accumulated evidences have correlated neutralizing antibody level with the immunity against covid-19. khoury and cromer et al. provided a model to predict the vaccine efficacy by comparing the neutralizing antibody titers of vaccines to those of convalescent samples. accordingly, the neutralizing antibody titer of the nanocovax injection group was 2 times higher than that of the recovered group, thereby estimating the protective effect to be about 90% against the original (wuhan) strain, and 75% against infection of delta variant. in addition, anti-s igg antibody at 3 months after vaccination with nanocovax vaccine was still higher than the antibody content of the convalescent group. comparing immunogenicity results of nanocovax with those of covid-19 convalescent patients evaluated by the pasteur institute in ho chi minh city, as well as with the immunological results from other licensed vaccines, it was shown that the nanocovax vaccine is effective in preventing covid-19. the national ethics committee for biomedical research concluded that the nanocovax vaccine estimated protective efficacy based on the immunogenicity data of the research ensured scientific validity, qualified to transfer the dossier to the advisory council for consideration. accordingly, all dossiers and data presenting information about the search for the only made-in-vietnam covid-19 vaccine have been submitted to the moh's advisory council for the registration of circulation of drugs and medicinal ingredients for emergency use authorization. economics the vaccine can cost up to 120,000 vnd or around us$5.2 per dose. nanogen currently possesses the ability to produce 10 to 20 million doses a year. the company is expecting to increase its capacity to 50-70 million doses a year to meet the domestic demand. nanocovax vaccine may be ready to deliver to the general public in the second half of 2021, if efficacy is shown. if the government goes ahead with the emergency decision, it may be rolled out in may, a nanogen official told nikkei asia in february 2021. on 26 march 2021, deputy minister of science and technology phạm công tạc and deputy prime minister vũ đức đam received the second dose of the nanocovax covid-19 vaccine. on 22 june 2021, general director of nanogen said in an interview that the company had applied for an emergency authorization of nanocovax in vietnam the week before.