Booster dose for everyone requires more data, says infectologist – 09/11/2021

The indication of a booster dose of vaccines against covid-19 for the entire population still requires more evidence, said today (11) the vice president of the SBI (Brazilian Society of Infectology) and clinical director of the University Hospital Clementino Fraga Filho, Alberto Chebabo, who says he has no doubts about this need for the elderly. The infectologist participated in the National Immunizations Journey and presented studies on what is known so far about the duration of immunity conferred by vaccines against SARS-CoV-2.

“I’m still not convinced that a third dose will be needed for the entire population. Right now, I have no doubt that it will be important for the population over 60 and immunosuppressed—understand who the immunosuppressed people are and why they are they need the booster dose. For the others, they need evidence, they need data, so we can make a better decision,” said Chebabo, who added that this dose could be extended to health professionals to reduce hospital infections and leaves of absence from work.

The infectologist explains that the vaccines currently used have played the role of reducing mortality and hospitalizations for covid-19, but have not yet managed to interrupt the circulation of the virus, especially given the emergence of new variants.

Other countries

Chebabo presented studies from the United Kingdom and Israel that indicate that vaccine protection against mild cases in the general population tends to diminish six months after the second dose, while protection against severe cases and hospitalizations appears to be longer lasting.

Therefore, the vice president of the Brazilian Society of Infectology argues that there are doubts whether a third dose will be able to produce lasting immunity against mild cases or whether the drop in protection against mild covid-19 will be repeated months after application and maintain a scenario conducive to the circulation of the virus.

“Important countries for us to evaluate would be Israel and the United Kingdom, which have different strategies,” pointed out Chebabo, who also highlighted Chile, where CoronaVac was the main vaccine used.

Israel applied only Pfizer’s vaccine, with a three-week interval between doses. When it detected a spike in positive tests for covid-19, the country decided to boost the immunization of the entire population with one more dose of Pfizer – six months after the second dose.

The UK used Pfizer and AstraZeneca, both 12 weeks apart. Experts are investigating whether the difference in the interval between the first and second doses can explain disparities in the effectiveness of vaccines against mild cases of the Delta variant, since one of the studies showed less protection among vaccinated people from Israel, in a comparison that considers only those who took Pfizer in the UK and Canada.

“We see that, probably, when we stretch this evaluation interval, with 12 weeks we get better protection”, commented the infectious disease specialist, who considered that the analyzed study was published in preprint and it still needs to be evaluated by other scientists.

herd immunity

The infectologist participated in a discussion table with the professor of infectology at Escola Paulista de Medicina and the clinical director of Grupo Fleury Celso Granato, who highlighted that the SARS-CoV-2 virus will require a high percentage of the immunized population to stop circulating.

“Establishing herd immunity to a virus that mutates in respiratory transmission is very complex,” he said. “There is, for any infectious disease, herd immunity, but the level is much higher than what we imagined, most likely 80%, 90%, something much closer to measles than to other less infectious diseases” .

For former coordinator of the National Immunization Program, Francieli Fantinato, the work of planning the immunization campaign against covid-19 leaves lessons, such as the importance of a strong and available advisory group to discuss new evidence and updates of the National Operational Plan of Vaccination against Covid-19, which is now in its ninth version due to constant discoveries about the disease and vaccines.