The antibodies provided by Covid-19 booster doses are not only effective at recognising the virus, but also neutralising it. — Filepic
A study involving 286 volunteers conducted during a surge of Covid-19 cases in Bahia, a state in north-east Brazil, reinforces the importance of a third dose of vaccine to protect against all main variants of the SARS-CoV-2 virus, including Omicron.
The study, which was published in the Journal of Medical Virology, found that people who had been given three doses of a Covid-19 vaccine had more antibodies capable of neutralising the SARS-CoV-2 virus than those who had not completed the primary vaccination schedule, and even people who had previously had Covid-19.
More than 80% of the participants who tested positive for the disease had not received the booster dose, which is normally administered after the standard two-dose scheme.
“Although some of the participants who had had the disease previously had more antibodies that recognised the virus, those who had received three doses of the vaccine had antibodies of higher quality, meaning they not only recognised, but effectively neutralised the virus,” said study last author Professor Jaime Henrique Amorim from the Federal University of West Bahia (UFOB).
Prof Amorim led the study, along with penultimate author Prof Luiz Mário Ramos Janini from the Federal University of São Paulo's Medical School (EPM-UNIFESP).
The study population consisted of patients with flu-like symptoms seeking treatment at a clinic in Barreiras, Bahia State, during an outbreak of the Omicron viral variant that occurred between January and March 2022.
Nasopharyngeal swabs and blood samples were collected from over 230 volunteers.
The viruses present in the swabs and samples were isolated and sequenced, confirming that they were Omicron.
Blood serum samples were then separated to test the action of antibodies on this variant and on the original Wuhan strain that gave rise to the pandemic.
“The antibodies found in samples from patients who had been given three doses of vaccine neutralised both the Wuhan strain and the Omicron variant.
"Antibodies from unvaccinated patients and patients given one or two doses did not,” said study co-author and EPM-UNIFESP post-doctoral fellow Dr Robert Andreata-Santos.
Only 16 of the vaccinated subjects who tested positive had taken a third dose.
Among the 189 who tested negative, 166 were vaccinated and 51 had taken three doses.
The study was conducted at a time when few people had taken a third dose of any of the Covid-19 vaccines then available.
Most had taken two doses of the Sinovac or AstraZeneca/Oxford vaccines.
Pfizer/BioNTech’s vaccine was then the most widely available for the booster dose.
“As expected, we found that vaccination does not necessarily prevent infection.
"What's new in our study is that people vaccinated with three doses had antibodies that neutralised even Omicron, which appeared when the vaccines in use already existed,” said study co-author Prof Luis Carlos de Souza Ferreira from the University of São Paulo's Institute of Biomedical Sciences (ICB-USP).
According to him, the results are globally relevant because they prove that booster doses of existing vaccines should be given to everyone, and also that the different combinations of vaccines administered in Brazil are efficacious in terms of protecting people against severe disease when infected even by recent SARS-CoV-2 viral variants such as Omicron.
“Most research on the third dose was done in countries of the northern hemisphere, which were more homogeneous in terms of the vaccine brands used.
"What we have now is relevant to Brazilian reality,” Prof Amorim said.
Preliminary results of a new analysis conducted recently by the group in the same city show that administration of a fourth dose also had a significant effect.
The researchers observed an even smaller number of cases of the disease even among people who were infected by the virus.
“The fourth dose appears to be as important as the third,” Dr Andreata-Santos said.
“Until vaccines produced specifically for novel variants are available, it’s vital to keep levels of neutralising antibodies high in the population, and that can only be done with booster doses.” – By André Julião/Agência FAPESP
