The world is observing a drop in hospitalizations, ICU bed occupancy and deaths caused by Covid-19, a result of the increase in mass vaccination, accompanied by the use of masks and physical distancing measures, even at a time of relaxation of restrictions. In countries where an increase in the number of cases is observed, this is happening mainly in unvaccinated populations. We are observing something similar in Brazil, with the pandemic entering a new phase. It is urgent to accelerate vaccination and guarantee a complete immunization regime for the Brazilian and world population, as the percentage of unvaccinated people is still very high and they are vulnerable to infection by the Delta variant, running the risk of developing serious forms of Covid-19. , which may require hospital care, which can lead to an increased risk of death.
Vaccination must be a collective pact
Only mass vaccination will control the pandemic and promote economic recovery. Vaccines against Covid-19 will only be truly efficient if there is high population adherence. Once vaccinated, you have a degree of individual protection, but vaccination must be a collective agreement. With many people vaccinated with the complete two-dose course or with the single dose of Janssen, everyone is better protected, including those who cannot be vaccinated for medical reasons. As the objective of all Covid-19 vaccines is to reduce severe cases, hospitalization and death, if you are infected, even if you are vaccinated, you will have a greater chance of having a milder case of Covid-19, in addition to having more opportunities for care. in hospitals, as the ICUs will be emptier if necessary. In the end, the higher vaccination rate leads to fewer serious cases and deaths from the disease.
But be very careful: This is not the time to relax in non-pharmacological measures
We have no evidence or justification to relax non-pharmacological measures such as the use of masks, physical distancing and hand hygiene habits. We need to maintain these health control measures and avoid closed spaces with crowds and poor ventilation. It is necessary to review the restriction measures, as there cannot be any precipitation, as relaxing at this time, with high circulation and rapid spread of the Delta variant, is very dangerous and we need to prevent vaccinated people from running the risk of becoming part of a chain again. of virus transmission. This could lead to a worsening of the health crisis, with an accelerated increase in infection among the unvaccinated and with a consequent increase in infection even in vaccinated groups, even those with both doses, regardless of the vaccine. The Delta variant is much more infectious than the original virus and more transmissible than the Gamma variant, leaving people infected with a much higher viral load.
Vaccination in Brazil is slow, but accelerating. Data from 04/08/2021 show that 147.698.704 million doses were applied, with 104.049.682 million people (49,14% of the Brazilian population) taking the first dose and 43.649.022 million people (20,61 .17% of the population) took the second dose + the single dose of the Janssen vaccine since 01/2021/19. People who do not take their vaccines, regardless of the reason, put everyone around them at risk and harm the vaccination program and the fight against Covid-XNUMX.
Anyone who took the first dose must return for the second dose
With the advancement of vaccination, the moving average of deaths from covid-19 continues on a downward trend, but according to data from the Ministry of Health released on 28/07/2021, around 4,6 million Brazilians are not they returned to take the second dose and complete the immunization cycle. Let's go back, guys. If you know someone who hasn't returned, talk to them and show them the importance of taking the second dose. As during this pandemic we never had a national awareness campaign for the Brazilian population by the federal government, so it has to be done by hand, it has to be from the bottom up. The recommendation for health departments is to actively search for these people, contacting them by phone or even sending health professionals to the addresses registered when these people took the first dose, but actively searching for 4,6 million people is dose, right? So let's join this fight.
What about the variants of attention and concern?
To date, the World Health Organization (WHO) has classified four variants as being of concern or concern. The Alpha variant is present in 182 countries, the Beta in 131, the Gamma variant in 81 countries and the Delta reached 132 countries. The Delta variant is a concern and is responsible for new waves of infections in Israel, the United Kingdom, the United States, China and Indonesia.
With the appearance of the Delta variant, more transmissible and with a greater ability to escape our immune system's response, we will need to vaccinate a greater number of people to reduce the percentage of susceptible people, preventing the virus from circulating among the most susceptible people. A CDC report, released by the newspaper The Washington Post also shows that the Delta variant is more transmissible than Ebola and smallpox, can infect already vaccinated people and cause more serious illnesses in unvaccinated people, when compared to other previous coronavirus variants and that both vaccinated and unvaccinated people are infected by Delta transmit the virus.
The report confirms that vaccines remain effective, especially after 2 doses, as other studies have shown in this British study e in this other study. The data shows that only small differences in the effectiveness of Covid-19 vaccines were observed with the Delta variant compared to the Alpha variant after receiving two doses of the vaccines. The differences in vaccine effectiveness were most striking after receiving the first dose. These results show the importance of vaccination and that people need the full two-dose schedule. Existing vaccines still work against the Delta variant, but may be less effective especially among people whose immune response is not sufficiently robust after vaccination, among the elderly and among people with comorbidities who have compromised immunity.
Find out what works against the Delta variant
This is not the time to relax in non-pharmacological measures, as the Delta variant is circulating and spreading and is considered much more transmissible than the previous ones. recent data suggest that the amount of virus in people infected with the Delta variant is about 1.000 times larger than in people infected with the original Sars-Cov-2 variant. And it doesn't hurt to remember that both vaccinated and unvaccinated people who have been infected by Delta can transmit the virus, although apparently people immunized with these fantastic vaccines in use today transmit less.
But do you know what also works against the Delta variant, in addition to vaccines? Non-pharmacological public health and social measures, such as the use of masks, physical distancing, hand hygiene habits, avoiding crowds in closed or poorly ventilated places. All of this works against the Delta variant and all vaccines prevent more serious cases and death. I am absolutely passionate about the vaccines in use against Covid-19 and the beautiful Science that has provided humanity with access to safe and effective vaccines.
What about collective immunity with the Delta variant? Do the calculations
It can get complicated. The Delta variant of the new coronavirus, if it becomes dominant, will make it very difficult for us to achieve so-called collective immunity. I show below a simple approximation of how experts estimate the percentage of people vaccinated to achieve so-called collective immunity in a scenario in which the Delta variant is dominant, which is not yet the case in Brazil.
The baseline reproducibility (R0), or the average number of people who are infected from a single infected individual, in this case by the Delta variant, is higher when compared to previous variants. The zero in “R0” means that this number is an estimate considering a scenario of zero immunity in the population. This number affects the percentage of people who need to be vaccinated with both doses or with single-dose vaccines so that we can achieve so-called collective immunity. In the case of R0 = 1 or lower, the infection will spread more slowly, may disappear, and most likely will not cause an epidemic in that population. But for this to be true, it is necessary to maintain sanitary and epidemiological control measures, such as non-pharmacological measures, testing and isolation of infected people and their contacts, in addition to genomic surveillance to monitor the emergence of new variants.
The higher the R0 value, the faster a disease can spread, but it is also important to consider that the rate of decrease in cases can be affected by the number of infected people who are cured and those who die. So, there are many factors that influence the time in which an individual can be considered infectious.
We can get a rough idea using the following formula to reach the herd immunity threshold, assuming that all individuals in a population are equally susceptible: [1 - (1 / R0)] x 100. That is, if R0 = 2, it means that an infected person transmits the virus to two other susceptible people, then [1 - (1 / 2)] x 100 = 50%, that is, we would need to vaccinate something around 50% of the population to achieve collective immunity, maintaining non-pharmacological measures and other epidemiological control measures.
The original Sars-CoV-2 virus had an estimated reproducibility of approximately 3, that is, each infected person could transmit the virus, on average, to 3 other susceptible people (R0 = 3), which led to an estimate that we would need around 66% of the population vaccinated to achieve collective immunity, using the following calculation: [1 - (1 / 3)] x 100 = 66%. From this percentage of vaccinated people, the virus' transmission speed would begin to slow down and could stop circulating, maintaining care with non-pharmacological measures. If the Delta variant causes one infected person to cause the disease in 5 other people (R0 = 5), for example, the percentage of people who need to be vaccinated to achieve collective immunity and begin to see a decrease in cases, hospitalizations and deaths, will be approximately 80%, calculated using the formula [1 - (1 / 5)] x 100 = 80%.
As the Delta variant is proving to be much more transmissible, it will most likely be necessary to reach a target of vaccinating around 80-90% of the population, which would include children under 12 years of age. For more information about these calculations, read on this page.
Third dose or booster dose? What's the difference
First, let's clarify what a third dose is and what a booster dose is. The third dose consists of the application of an extra dose that serves to complement a single vaccination cycle, a few weeks after the application of the second dose. A booster dose, which may be with the same vaccine previously applied or may involve another vaccine platform, is a vaccine that is applied annually or at some frequency, to reinforce the first cycle of immunizations and so on.
At the moment, we do not have scientific data showing that we will need a third dose or booster shot for any of the Covid-19 vaccines. We still do not have results proving the effectiveness of a booster dose, nor data showing that this is necessary or even beneficial. Then, we have to wait for the results of the scientific studies being carried out, as decisions about the future vaccination strategy must be based on robust scientific evidence. We should not simply think that the more doses of vaccines we take, the more we will be protected.
Experts remember that the immune response against any antigen in any vaccine tends to drop after a while, and in the case of Covid-19, Science is still trying to understand how this drop happens, after how long and what the effect of each new variant of attention.
Although vaccination is accelerating in Brazil, as previously stated, the level of collective immunization is still insufficient to have a sustained drop in the dissemination and spread of the virus. We reached 49,14% of the Brazilian population vaccinated with the first dose and 20,61% of the population who took the second dose or the single dose of the Janssen vaccine. This is over a period of 6 and a half months, so we need to speed up vaccination even further.
The important thing is to carry out studies to identify which populations are more vulnerable to reinfection by the new variants or even to having more severe symptoms of the disease, even having been vaccinated with two doses of any vaccine or a single dose of Janssen. Yes, a third dose may be necessary, especially for immunosuppressed people, those who have had solid organ transplants, older people, people with a more compromised immune system and health professionals, who are more exposed.
It is very important to clarify this point so as not to bring more insecurity to the population. Some European countries are adopting a third dose, and Israel decided to vaccinate the population over 60 years of age with a third dose. These countries are much more advanced than Brazil in terms of vaccination and the Delta variant is infecting the unvaccinated, and could also infect the vaccinated, especially the most susceptible.
What about vaccine interchangeability?
In Brazil, the Ministry of Health commissioned a study that will be conducted by the University of Oxford, with the aim of evaluating the need for a booster dose or a third dose of vaccines against Covid-19. The study will involve 1.200 volunteers over 18 years of age, who have already taken two doses of the CoronaVac vaccine and will take a third dose of one of the four vaccines in use in the country: CoronaVac, AstraZeneca, Janssen or Pfizer.
Butantan will not participate in these clinical studies, but is evaluating the application of an additional dose of CoronaVac to residents of the city of Serrana, in the interior of São Paulo, where the S study with mass vaccination was carried out and has shown fantastic results. Butantan also reported that it is studying the possibility of an annual vaccine booster, which should not be confused with a third dose, to increase the effectiveness of CoronaVac. In the case of a third dose of vaccines from AstraZeneca, Janssen and Pfizer, the objective is to determine the best option as a vaccine booster for those who have taken two doses of CoronaVac. This will be an interchangeability or heterologous vaccination study, as it involves different platforms.
Two other similar studies being carried out in Brazil and authorized by Anvisa, will evaluate the safety and effectiveness of a third dose, the first of which involves a homologous vaccination study, which investigates the effect of applying a third dose of Pfizer vaccine in people over 16 years of age who have already taken two doses of the Pfizer vaccine. Data from a study conducted by Pfizer in the United States show that the extra dose creates antibody levels around five to ten times higher.
O second study will evaluate the application of the AstraZeneca vaccine, already updated for the platform containing the genetic material of the Beta variant, from South Africa. In this study, two arms will be tested, with the first, homologous vaccination, the third dose of the vaccine of the updated AstraZeneca vaccine will be applied to the same volunteers who have already taken two doses of the AstraZeneca vaccine in Phase 3 studies, between 11 and 13 months after the second dose. It will be a controlled, randomized, single-blind study, that is, in which only the volunteer will not know what he took: whether an extra dose of the updated vaccine or a placebo. Pregnant women, people with comorbidities or those who have had Covid-19 will not be included.
The second arm of the study will involve a heterologous combination trial, with the updated AstraZeneca vaccine being given to people who have had two doses of Pfizer's messenger RNA vaccine. These studies must evaluate the safety, efficacy and whether the third dose of the vaccine is capable of producing a significant immune response.
So let's wait for Science's response, folks. It is natural that countries that are very advanced in immunization begin to worry about this issue of the third dose. But perhaps this is not our case yet, as we have a large percentage of our population not yet fully immunized and we have few vaccines
What we have to do at this moment is to vaccinate everyone quickly to reduce the circulation of the virus, serious cases and deaths. And in this sense, vaccines are giving a wonderful and extraordinary response and are showing the way out of the pandemic. Vaccines alone will not stop community transmission, so people need to continue to wear masks, stay in well-ventilated places, practice hand hygiene, maintain physical distancing and avoid crowds and places with poor ventilation. It is also essential to test to isolate infected people and their contacts.
Vaccination is necessary; vaccinating is living; living is imprecise.
Observation: This text is the responsibility of the author and does not necessarily reflect the opinion of Unicamp.
