Although they are administered differently, the objective is the same: strengthening the immune response to SARS-CoV-2.
There are still lots of questions about COVID-19 vaccines. According to three experts consulted by Tec Review, the reliable vaccines are those which have achieved an efficacy rate of above 90% –after one or two doses– and have passed or are about to pass Phase 3 tests involving trials on tens of thousands of people around the world.
“Slow production of vaccines has hindered their worldwide distribution. For this reason, the recommendation is to apply the vaccine that is available (two-dose vaccines right now or one-dose vaccines when they become available) given their excellent efficacy rates,” says Reynaldo Lara Medrano, an infectiology specialist at TecSalud.
He adds that, once the pandemic is under control, the best options can be determined using the statistics collected.
This point of view is shared by Graciela Castro Escarpulli, a researcher at the National School of Biological Sciences (ENCB) of the National Polytechnic Institute (IPN), who explains that one- or two-dose vaccines do provide protection, although it is not yet known for how long.
“Perhaps it will be necessary to get vaccinated every year like we do for influenza,” says the IPN scientist.
This is because vaccinated people may not develop a permanent immunity.
“There is also the possibility that people who are vaccinated will get infected again but not get sick, i.e. they may have an asymptomatic infection,” says Susana López Charretón, a researcher at the Institute of Biotechnology of the National Autonomous University of Mexico (UNAM).
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This scientist explains that the pharmaceutical companies developing Covid-19 vaccines already have experience making previous vaccines on their platforms, which determines how the vaccine will be administered.
“For example, Janssen is only going to give a single dose because they have previous experience with an Ebola vaccine using the same recombinant adenovirus system. They know that a good immune response can be achieved with one dose,” explains López Charretón.
Meanwhile, other companies like Pfizer or Moderna have concluded that it is necessary to administer two doses in order to achieve immunity levels similar to Janssen’s.
“They have seen that the second dose improves the immune response a little more, giving the best result. That’s why they decided to do it like that,” she says.
In these cases, according to López, it means that the first dose provides an approximate protection rate of 60%. The second dose raises it to 90%.
The Mexican government has pledged to purchase around 200 million doses of the two-dose vaccines from Pfizer, AstraZeneca, and Covax, as well as one-dose vaccines from CanSino, according to a post on Twitter by Jesús Ramírez Cuevas, the president’s general coordinator for Media Relations.
Recently, President Andrés Manuel López Obrador also agreed to purchase the two-dose Sputnik vaccines following a telephone call with Russian President Vladimir Putin.
TecSalud, the health system of Tecnológico de Monterrey, has announced that it will conduct Phase 3 clinical trials on the German CureVac (two-dose) vaccines in Mexico.
If people got only one of the two vaccinations, they would have partial immunity but that is not ideal.
“Not completing the process means you aren’t completely safe. The population would be half-protected and that is very dangerous. We need a population that is fully protected in order to reduce the viral load and reduce the number of patients,” warns López.
On the other hand, she explains that people are wrong if they believe that only Covid-19 vaccines with efficacy rates of above 90% will work.
“Really, anything over 75% is a very good vaccine,” she concludes.