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Through the eyes of a specialist: Isolation of SARS-CoV-2, immunogenicity, booster dose and vaccination on individuals that already had Covid, on the second day of the CoronaVac Symposium

Publicado em: 01/01/1970

On this second panel of the symposium regarding CoronaVac, a diversity of aspects about the immunogenicity of CoronaVac was discussed. The session was coordinated by Dr. Renato Mancini Astray, Scientific Researcher from Butantan Institute, and Dr. Yiming Shao, from the Control Center of Diseases from China.

The first lecture was ministered by Dr. Edison Luiz Durigon, professor of Virology from the Department of Microbiology of the Biomedical Science Institute of USP and had as a theme “Neutralizing antibodies for SARS-CoV-2: The brazilian experience”. Doctor Durigon highlighted the importance of the Virology Lab NB-3 of USP in the isolation of clinical samples from the first patient diagnosed with SARS-CoV-2 in Brazil. The isolation happened in a classic way, by the incubation of clinical samples in layers of Vero cells. The virus isolated and titrated was distributed to all the labs of NB-3 levels of the country, allowing a quick establishment of the diagnosis methods. The Lab was also able to quickly standardize the neutralization trial by cytopathic effect, known as VNT. In this trial, the serum to be tested is diluted in a serial way and incubated with a known quantity of the virus. Then,  a combination of serum and virus is transferred to the Vero cell culture and the cytopathic effect of the virus is evaluated after 72 hours. The result is reported as the highest dilution of serum capable of neutralizing the cytopathic effect of the virus. The group used the VNT test to evaluate the neutralizing antibodies of the individuals vaccinated with CoronaVac. The results of two cohorts demonstrates that, after the second dose, the CoronaVac induces the production of neutralizing antibodies on high titers, reaching the number of 640, for the strain Wuhan, P1 (gamma), P2 (zeta) and delta. The titers reach a peak between 30 and 60 days after the second dose, and afterwards there is a decrease, but are still detectable 5 months after the vaccination, and the immunological memory prevails. The follow up of some vaccinated patients that contracted the disease clearly showed that the vaccinated individuals, even after 6 months of the vaccine, has a really fast response to the infection, with an abrupt increase of the neutralizing antibodies titers, that contributes for a lighter symptomatology.The results presented by Doctor Durigon clearly demonstrates the immunogenicity of CoronaVac.

The immunogenicity of the vaccines has a direct correlation with its efficiency on the general population. In this context, the Doctor Zhijie An, from the Yunnan University from China, spoke about the progress of vaccination in China against Covid-19 and the efficacy data in the real world against the variant delta.Evidence from the real world complemented the data from a clinical trial of a vaccine, providing information from populations that are different from the clinical trial population, in different epidemiological situations, with different closes or against different pathogen strains.Since the beginning of the big outbreak of the infeccion by the virus SARS-CoV-2, China initiated an intense process of virus contention, diagnosing the cases and isolating in hospitals, focusing on the control of the communitary transmission. This way, even without available vaccines initially, the population was accessible to the virus, but with a low risk of infection. Nowadays, China has 7 different vaccines approved by the Chinese Regulatory Agency, most of them from inactivated viruses. Two of these vaccines are included in the official list of OMS. The global efficacy of the vaccines used (inactivated, adenovirus and of recombinant protein) was of almost 100% of prevention of serious cases, reducing the risk of sickness. Between May and June of 2021, an outbreak of the Delta variant was discovered and tracked on the Guangdong province, in China. Before this outbreak, Guangdong had begun mass vaccination using inactivated vaccines approved for use in adults. The researchers were benefited by the control protocols of China, which allows them to identify, put on quarantine and test all the close contacts to any infected person with SARS-CoV-2. This way, it was possible to determine the vaccination status of these close contacts and keep track of  which ones were infected. The study allowed them to estimate the effectiveness of the vaccines used in Guangdong against the Delta variant, in conditions of real life. The researchers monitored 12.501 individuals that were close contacts of the confirmed cases though the lab, categorizing them in groups (a) non vaccinated, (b) partially vaccinated and (c) fully vaccinated (14 days after the second dose, in a vaccinal scheme with 21 days of gap). The effectiveness of the complete vaccination was about 77% against pneumonia and 100% against serious diseases. The incomplete vaccination was not so effective against pneumonia (around 8%), but serious cases were not registered in this group, while 19 individuals of the non vaccinated groups presented critical or serious cases. Other similar studies were realized in other locations, like Jiangsu in China, and in the population of Chile, with similar results, reducing about 90% of the risk of evolution of light cases to serious cases, on individuals with the complete vaccine scheme. The studies proved the effectiveness of the inactivated virus vaccines against the variant Delta of SARS-CoV-2 and corroborated the necessity of guaranteeing the complete vaccination of the target population.

Doctor Xiangxi Wang, from the Biophysics Institute of the Chinese Academy of Science, punctuated in a more structured way the interaction between antigen/neutralizing antibodies and the importance of the administration of a third dose of inactivated vaccine. The pandemics is lasting almost two years and lots of vaccines were used during the last year and the advance in the end of the pandemics is being too slow, because of different reasons: one of them is the emergence of variants of concern (VOCs), like alfa, beta, gamma, delta and the most recent one, Omicron, that seem to be more resistant to the neutralizing antibodies since it has different mutations in the region of the Spike protein. As an example, Omicron, which possesses more than 30 mutations on the spike protein. Another reason is the reduction of the neutralizing antibody quantity with the passing of time after the vaccination or natural infection. A plausible approach to solve the problem is the administration of a booster dose of the vaccine between 6 to 12 months after the second dose, to improve and extend the protection. The serological analysis of plasma samples of individuals that received three doses of the vaccine with inactivated virus shows an increase in the titers of neutralizing antibodies and protection against the coronavirus variants, when compared to the plasma samples that received two doses of the vaccine. The administration of a third dose increased the production of neutralizing antibodies 20 times, 2 weeks after the vaccination, being stable after 6 months of the booster vaccination. The study evaluated the profile of antibodies of volunteers that received two or three doses of the CoronaVac vaccine, COVID-19 convalescent and healthy participants, with the intent to compare the immune humoral responses induced against variants on circulation of SARS-CoV-2. The number of mutations on V gene nucleotides (variable) on the antibodies of individuals vaccinated with three doses is higher than on individuals vaccinated with two doses or convalescent individuals. This shows that the highest mutation on these antibodies is also the highest bonding   and neutralizing activity. Therefore, it was analyzed almost 200 complex structures of neutralizing antibodies to SARS-CoV-2 and identified correlation between the structure and the activity, revealing ultra-potent antigenic fixes, resistant to the variants and of broad spectrum over the RBD, including the most recent variant, Omicron.  This demonstrates that the continuous somatic mutation of antibodies and the clonal renovation of the B cells of memory induced with three doses of the vaccine stimulate and increase the potency and amplitude of neutralization.

In sequence, Doctor Ahmet Soysal, from the Atasehir Memorial Hospital in Turkey, approached the vaccination with CoronaVac on individuals that were previously infected. Initially, Dr. Soysal contextualized the updated epidemiological data from Turkey and highlighted that most of the deaths nowadays in the country corresponds to the non vaccinated individuals. Doctor Soysal reported that there is not a guideline of how long after a natural infection an individual is apt to receive the first dose of the vaccine, reason why the study was realized, so it could compare the titers of antibodies and the adverse reactions induced by CoronaVac on health professionals that were previously infected or not. The adverse reactions were obtained by online tests or phone calls, seven days after each dose of the vaccine. The detection of antibody levels was evaluated considering the recognition of the RBD domain from the protein spike SARS-CoV-2, four weeks after the second dose of the vaccine. The vaccination of health professionals previously infected occured after 64 days, average time (gap: 15 - 136 days). From these volunteers, 40% were asymptomatic, 50% had light infection of the superior respiratory tract, 10% had pneumonia and 5% were hospitalized. Differently from what was related from other vaccines, there was no difference on the adverse reactions related to the vaccination among individuals previously vaccinated and non vaccinated, on first and second dose of the vaccine. The most common symptom reported was pain on the local of the vaccine and most of the adverse reactions were mild  (level 1). The average titers of antibodies anti-RBD were significantly higher on health professionals that had a natural infection before than the health professionals that were not infected. In summary, the study demonstrated that the CoronaVac vaccine induces antibodies response on non infected individuals with SARS-CoV-2 and on individuals that were previously naturally infected; the average of the antibody response was higher on individuals that were infected previously. The administration of CoronaVac was safe and can induce a higher response of antibodies on individuals that were previously infected.

During his speech, Dr Alexis Kalergis, of the Pontifical Catholical University from Chile, says that they formalized the collaboration with Sinovac in the beginning of 2020, which led to a beginning of a clinical study. The clinical trial of phase 3 realized in Chile, using the CoronaVac, included different centers, with volunteers that received two doses of the vaccine and volunteers that received placebo, with gaps of two weeks between the doses. The immune response in healthy adults two weeks after the second dose was a significant increase of anti-RBD antibodies in most of the individuals. Using tests of direct neutralization and with pseudovirus, there was a significant increase two weeks after the second dose of CoronaVac on healthy adults and eldery. They did a lot of analysis on TCD4+ and TCD8+ cells and saw that after 2 and 4 weeks after the second dose they were able to detect the presence of T cells using peptides derived from proteins of the virus. The clinical study is still being conducted in collaboration with Brazil, Turkey and Indonesia, and is still ongoing simultaneously. This scientific collaboration led Chile to be one of the countries with the highest number of  vaccinated people in the world. The benefits after some months showed that the vaccination campaign is considered one of the main reasons for the reduction in Covid-19 cases that Chile had in the last 5 months, showing that the vaccination in the real world really works and is positive for the population. With the natural decrease of the immunity 6 months after the vaccination, Doctor Kalergis recommends the use of a booster dose in Chile, which is part of clinical study that demonstrates that after the third dose, the level if antibodies increases quickly, having even higher levels than after the second dose, showing the same for the capacity of antibodies neutralization. They were able to detect TCD4+ cells productors of IFN-γ even after 20 weeks of the third dose. Study with the pediatric population with 3 and 17 years of age began, and the results are really positive, similar to the ones seen on adults. So, Doctor Kalergis spoke about the importance of transparency and dialoguing with the press every time they are requested to, so it can stimulate the vaccination.

The session ended with a great discussion over the immunogenicity, safety and importance of a third dose of CoronaVac. 

Highlight of the day

“If we want to stop the infection, we must have high titer levels of neutralizing antibodies constantly to avoid the virus entering into the cell and starting the disease. But if we want to stop the disease or the pandemics, we don’t need to have high levels of antibodies, we can have the memory for that, and the antibodies increase quickly and protect us against the severe form of the disease.” - Doctor Edison Luiz Durigon.