Coronavac vaccinated may need 4th dose, study suggests

Two doses of the inactivated Coronavac virus vaccine induce the body to produce neutralizing antibodies against the original form of the coronavirus and other variants of concern (VOCs) that have emerged, such as delta.

But when the omicron comes into play, Coronavac vaccinates have a very low, almost zero, capacity to neutralize this variant, compared to those vaccinated with two doses of mRNA vaccines.

When those immunized with the inactivated virus vaccine receive a booster dose from Pfizer, this antibody-conferred protection increases, although it is still slightly lower than that seen with messenger RNA immunizers, which may suggest the need for a extra booster dose.

These are the results of a study conducted by Akiko Iwasaki, a researcher at the Immunology Laboratory at Yale University.

The pre-print describing the study, still without peer review, was published on December 29 on the medRxiv platform, and therefore deserves caution in the analysis of the results, but the Iwasaki laboratory is renowned and internationally recognized as a reference in studies of immunology.

The research investigated the neutralization capacity of vaccines against the variant, which is currently dominant in almost all countries where it has spread, and other forms of the ancestral virus.

Neutralization is the protection provided by neutralizing antibodies, responsible for blocking the entry of the virus into cells, but vaccines also induce other immune responses, such as cellular protection, offered by T lymphocyte-like defense cells, and the production of antibodies against other parts of the virus.

To assess the protection against the micron, the researchers looked for the rate of neutralizing antibodies, which bind to the virus’s Spike S protein, and of the IgG type, specific against the region of Sars-CoV-2 known as RBD (binding domain). with the recipient) in blood samples from 101 subjects in the Dominican Republic.

As a control group, the researchers compared the values ​​found in the Dominican population with those observed in blood samples from Yale University health workers who received two doses of mRNA vaccines (Pfizer or Moderna).

After the blood was collected, the scientists tested the blood plasma — the portion of the blood that contains the antibodies — in the laboratory against the different viral strains.

The researchers confirmed that some variants, as expected and already demonstrated, lead to a decrease in the protection provided by vaccines after a certain time (four months). A booster dose of Pfizer in Coronavac vaccinates raised levels of protective antibodies against the parent strain and against delta by ten and sixfold, respectively.

Even those vaccinated with two doses of Pfizer or Moderna showed a reduction in the rate of neutralizing antibodies against the omicron that was up to 12 times lower than that observed against the ancestral virus.

In the case of Coronavac, those vaccinated with two doses had practically no antibodies against the micron. With the Pfizer booster, the amount of antibodies in the blood increased considerably.

On his Twitter account, Iwasaki stated that this data may indicate the need for two booster doses in individuals vaccinated with Coronavac to protect against the micron.

Unlike other studies, Iwasaki’s research did not find better protection conferred by antibodies produced post-vaccination in people who had been previously infected with the virus.

Even in people who received two doses of Coronavac and a Pfizer booster and already had Covid, the antibody rate was not enough to block the omicron.

According to the Brazilian Carolina Lucas, who participated in the study, the results should be interpreted with caution. “The data suggest that the micron is associated with a lower efficacy of vaccines against the micron, even after a heterologous booster, which can result in the so-called ‘vaccinal escapes’. However, vaccines are still extremely efficient in preventing a condition more serious clinical condition and deaths”, he says.

Vaccines against Covid-19 were developed, in large part, to stop the disease from developing, but results from clinical trials and mass use around the world indicate a limited ability to prevent infection.

Because of this, countries around the world rushed to speed up booster doses of the Covid-19 vaccine and try to stop this new variant.

The result worldwide, although it has been an exponential increase in new cases, seems to have had an effect with regard to hospitalizations and deaths, with a lower rate of hospitalized and dead in this new wave of the pandemic.

In early December, Sinovac announced that it is developing a Coronavac update that is effective against the onomicron and that it should be available by March 2022.

A study published last Sunday (2) by researchers at the University of Science and Technology of Hong Kong in partnership with the University of Melbourne shows that defense T cells maintain good protection against the micron even when neutralizing antibodies fail to block the virus entry.

T cells do not prevent infection by the coronavirus, but attack the virus in the cells, preventing its propagation and the occurrence of the so-called cytokine storm, associated with the most aggravated condition of Covid.

Some studies suggest that the omicron also causes less severe illness by infecting the lungs less, which may also partially explain the lower rate of hospitalized with severe illness.

Lucas, who has been a postdoctoral researcher in the Iwasaki lab since 2018, stresses the need for booster shots. “Our data support the idea that the Ômicron is associated with a greater immune escape than other variants already described, not only against vaccines, but also in relation to post-infection immunity, highlighting the global need for booster doses to combat the disease. pandemic”.