Brazil is starting to prepare to apply the third dose of vaccines against Covid in an unusual situation: it is in an intermediate group of vaccine coverage considering the population with at least one dose, but it has low coverage of those with full immunization.
The country has already reached 62% of the population immunized with at least one dose, a percentage that is even higher than the 60% in the United States. But it has only 28% with full immunization, compared to 51% of Americans (Thursday 26 figures).
Among the 130 countries with available data, only two have such a wide gap between those who took the first dose and those who are fully immunized (Costa Rica and Taiwan).
The difference in Brazil is 34.3 percentage points between the two groups; Costa Rica is 39.4 points; and Taiwan, 37.1.
Brazil is the 22nd with the highest proportion of vaccinated with at least one dose, but the 48th considering full immunization.
Almost 70 million Brazilians have started, but have not yet completed the vaccination schedule, according to data collected by the consortium of press vehicles.
Studies show that the first dose provides some protection against the disease, although the effectiveness can vary greatly depending on the manufacturer. The second dose, however, is essential to raise immunity to safer levels and promote it for longer periods.
Recent surveys show that this phenomenon is even more evident with the delta variant—the first dose has lost much of the expected protection against the mutation, but the loss after the second is more subtle.
Nations such as Denmark, Germany, Canada, Chile, Israel, Hungary and the United States have already started or will soon start the application of extra booster doses, whether in the most vulnerable, such as the elderly and immunosuppressed, or in broader groups.
All of them, however, have at least half of the population fully immunized (vaccinated with the second dose or the single dose vaccine). Even countries that started vaccination almost at the same time or after Brazil, such as Japan, Jordan and Colombia, already have larger shares of the population with the complete scheme.
Despite arguing that the third dose is important, especially for specific audiences such as immunodepressed and elderly people over 80 years of age, epidemiologists heard by the report stated that ensuring the application of the second dose for the population should also be a priority.
There are two ways to speed up this process: with more active search for those who already can, but have not yet taken the second dose, and shortening the interval between doses. This second option has started to take shape in the country.
Experts also point out two reasons why complete immunization is disproportionately slow in Brazil: the fact that a large contingent does not return for the second dose (there are more than one million missing in the state of São Paulo alone) and the long time. interval between applications for those taking Astrazeneca or Pfizer.
Both have a 12-week period between the two doses, although some states have recently reduced this time to 10 or 8 weeks.
In the case of Pfizer, the manufacturer recommends that the wait is 4 weeks. Following the strategy of the United Kingdom, Brazil adopted a longer period to be able to immunize more people with the first dose, since there is a shortage of immunizers. The explanation was that studies indicate that the first dose already confers some immunity against the coronavirus, although less than in the full regimen.
Epidemiologist and professor at the Federal University of Rio Grande do Sul, Paulo Petry says that the decision to space the doses to quickly expand the portion of the partially immunized population was correct.
“Before the delta, we had all indicators decreasing: cases, hospitalizations, admissions to ICUs and deaths. This drop is certainly due to vaccination. The problem with having a new variant now is the risk of new peaks”, he says.
The experience in other countries, especially in Israel, has lit the alert for a possible vulnerability of the elderly, who have a less efficient immune system than younger people. Therefore, the vaccine may be less effective for them, who are already a group more prone to complications from Covid.
Israel, which was celebrating the success of the vaccination campaign, saw the number of cases and deaths rise again with the arrival of the delta variant, with greater impact for the elderly. With that, he started to apply a third dose for reinforcement.
There are indications that this effect may occur in Brazil, although there is still little data available. The government of Rio de Janeiro stated that there was a high number of hospitalizations among vaccinated elderly, and a recent Fiocruz bulletin indicates that the current trend of falling cases and deaths could be reversed very soon.
The institution also carried out a study that shows that the effectiveness of vaccination is lower in those aged 80 or over, especially in the case of Coronavac. The drop in protection is even greater for those who are 90 and older.
For epidemiologist Ligia Kerr, member of the technical chamber of the National Immunization Program and vice president of the Brazilian Association of Public Health, the results reinforce the need for an extra dose in the elderly.
“It was the groups that were first vaccinated. We know that, in the case of Covid, the immune response to the infection drops over time, and the same happens with vaccination”, he says.
This does not mean, however, that the second dose can be left for later. “The percentage of Brazilians with the two doses is low to face the delta. We have to run with the vaccines, and it is worth remembering that the use of masks is absolutely essential, in addition to keeping distance. This strain has an extremely high viral load.”
André Giglio Bueno, infectious disease, professor at PUC-Campinas and curator of the HubCovid platform, says that the scenario is now different from the beginning of the vaccination campaign, when there was a great shortage of doses.
If the vaccine delivery schedule is met, he says, it will be possible to associate the completion of the population’s vaccination schedule with the administration of the booster dose in the elderly and immunocompromised.
“Even as a matter of prioritization, it will not be all the elderly who will receive the third dose in this first moment, but those aged 70 years or more. Even the immunosuppressed are a restricted group. The main objective is to reduce hospitalizations and deaths, and the decision was the right one”, he says.
Along with the announcement of the extra dose, the Minister of Health, Marcelo Queiroga, stated that the interval between doses of Astrazeneca and Pfizer vaccines would be reduced to 8 weeks.
He said that this would be possible from September, when the entire adult population would already be able to receive the first dose. Until this Thursday, 82% of Brazilians aged 18 and over had received at least one injection.
The strategy of advancing the second dose was adopted in other countries. In Germany, for example, the range is shorter in cases where the second dose is from a different manufacturer than the first — a mixture that experience suggests may boost immunity to Covid.
Petry, from UFRS, agrees with the need to anticipate the second dose given the delta threat. He, however, is not so sure that the number of vaccines in the country is comfortable and points out that there is still a portion that has not even received the first dose — 26% of those who are 12 years old or more, the target population of the campaign at the moment.
“The delta is very transmissible, it should be reduced [o intervalo entre doses]. Of course then we will have more people with complete immunity, but on the other hand we will have fewer first doses. There is also reinforcement for the elderly, immunocompromised people and, in my opinion, it would also be necessary for health professionals, who took the second dose in March. It’s a puzzle.”
There are significant differences between Brazilian states. While 35% of Paulistas received both doses or the single dose vaccine, there are less than 15% of Amapáenses in this situation.
The Federal District, on the other hand, has the largest gap between the population with at least one dose and the fully immunized population (41% of the inhabitants have only partial protection).