One of the important ways to control the COVID-19 pandemic is to producean effective vaccine. Currently, various vaccines generatedby different methods are being used all over the world with emergency use approval (2). When the effectiveness of vaccines in use are examined; Pfizer / BioNTech, Gamaleya, Moderna and AstraZeneca announced the vaccine efficiency as 95%, 92%, 94.5%, 70%, respectively (8, 9, 10). For the CoronaVac vaccine, efficacy statements have been received from different countries at different rates (50.4%, 65.3, 78, 91.25), and these data have not been published yet (11, 12).
Recently, different SARS-CoV-2 variants have brought some reservations about the effectiveness of vaccines. It is thought that the immunity created by the vaccine against some variants may not be effective. It is stated that especially mRNA vaccines will need to be revised (13–15). However, Iversen and Bavari stated that compared to vaccines targeting only spike protein, inactivated vaccines would provide additional benefit as they target many SARS-CoV-2 proteins (16). Another drawback regarding vaccines is whether or not a booster dose will be required. In a study conducted with healthcare workers infected with SARS-CoV-2, it was shown that neutralizing antibody levels decreased over time. Therefore, it has been suggested that booster vaccination may be required periodically (17).
SARS-CoV-2 vaccines have been developed very rapidly and because of this they have brought some concerns in terms of long-term side effect profile. Anaphylaxis is one of the important life-threatening side effects and there are concerns that it may be more likely to be seen in mRNA vaccines (12, 18–20).
CoronaVac 600 SU/0.5 ml (Sinovac Life Sciences, Beijing, China) vaccine, which is an inactive COVID-19 vaccine isbeing used after obtaining emergency use approval in our country (3). The vaccine is administered intramuscularly in 2 doses, 28 days apart. When the literature was examined, it was found that real-life data on CoronaVac vaccine was not shared before. The data in our research is the first real-life data of CoronoVac vaccine and is important in this regard.
Another issue is how protective the antibodies against SARS-CoV-2 are. In the study conducted by Lumley et al., itwas shown that the incidence of COVID-19 in healthcare workers with SARS-CoV-2 IgG positivity was significantly lower. Antibodies against spike protein and / or nucleocapsid have been shown to be protective (21). In the study conducted by Borgonovo et al.,itwas shown that IgG formed against spike protein continued for 7 months and symptomatic COVID-19 infection did not develop in these people (22). In another study by Zhang et al.,itwas shown that B lymphocyte response developed in the first 14 days after a single dose of CoronaVac vaccine, but T lymphocyte response developed after the second dose (23). When the data of our study were examined, the rate of antibody formation after the second dose of vaccination in all individuals was found to be 100%. These data show that the CoronaVac vaccine is effective after two doses.
There are some limitations in our study.One of them is being conducted in a single center with a small number of people. In addition, cellular immunity was not evaluated and protection was measured only by the antibody level. In this context, multi-centered studies consisting of larger groups evaluating antibody and cellular immune response level after first and second dose of vaccination are needed.
In conclusion, antibody development level was found to be 100% after two doses of CoronaVac vaccine. It can be said that two doses of CoronaVac vaccine create an effective humoral immunity. Therefore, two doses of CoronaVac vaccine application is effective against SARS-CoV-2.