Penelope Canonico
04/03/2021 6:00 AM
Clarín.com
Society
Updated 04/03/2021 6:00 AM
In a context of
global shortage of vaccines against the coronavirus
, numbers of infections on the rise and without a predictable horizon for the arrival of all doses, the Government decided a week ago to change the strategy in vaccination.
The Federal Health Council recommended delaying the second dose for all Covid vaccines for at least 12 weeks with the intention of prioritizing the application of the first component in operational implementation.
Immunize more people with the first and defer the second.
One of the questions that still does not have a satisfactory answer is
how long will the production of antibodies last
and, consequently, the ability to defend against infection by this new coronavirus.
Another issue is the permanence of efficacy if the second dose is not given within the recommended time frame.
Based on studies in infected patients, it is believed that the
immune memory
conferred by these vaccines will last for at least one year.
The question then arises whether delaying the application of the second dose for three or four months could affect the efficacy of the vaccines and / or the durability of the memory they induce.
Of the three vaccines that are applied in Argentina (Sputnik V, Sinopharm and AstraZeneca / Covishield),
the only one with scientific evidence
to delay the second dose for at least 12 weeks is AstraZeneca (renamed Vaxzevria).
However, Guillermo Docena, biochemist, immunologist and principal investigator of Conicet, suggests that, with a dose of the Sputnik vaccine, the immunity should be durable as with that of AstraZeneca.
"By having the two adenoviral vector vaccines,
the same thing that was observed in one should happen with the other,
" said the scientist, who is participating in a study on the immune response of the Sputnik V vaccine in vaccinated people from the province of which they form The Leloir Institute, the Institute for Biomedical Research on Retrovirus and AIDS (INBIRS) and the Institute for Immunological and Physiopathological Studies (IIFP) of La Plata are part of it.
Following the same line, Jorge Geffner, senior researcher at Conicet, adds: “Studies carried out in the United Kingdom have shown that the effectiveness of the Oxford / AstraZeneca Vaccine would not be compromised,
nor would the extension in time of the immune memory that it induces.
.
It is logical to assume that what is observed in the United Kingdom can be extrapolated to other vaccines also based on adenoviral vectors, such as Sputnik V. In fact, research carried out in our country has shown that the application of a single dose of Sputnik-V generates 90 % of vaccinated individuals significant levels of antibodies ".
Geffner clarifies that “it remains to analyze in a particular way
the response induced by Sinopharm
, prepared on the basis of inactivated whole viruses, in order to establish the convenience or not, of delaying the application of the second dose, in order to reach a a shorter period of time to a broader segment of the population, in the first place, to those over 60 years of age ”.
Efficacy and antibodies
How effective are these vaccines?
Martín Stryjewski, Head of Hospitalization at CEMIC and Master of Health Sciences from Duke University, details that AstraZeneca is up to 76% effective (ability to prevent infection) at three months with a single dose, "
but not it reduces asymptomatic cases with this scheme
: it only has an effect on clinical disease, preventing three out of four infections ".
Sputnik V is 73% effective until day 21 and Moderna (which is not used here) is 62% at 28 days, both before the second dose, Stryjewski explains.
Carlos Regazzoni, doctor and former head of PAMI, adds: “Globally these vaccines are effective with two doses, ranging from 70% to 90%, to prevent severe diseases and deaths, but it
is reduced by 30% with a single dose, and it will probably last less time
(how
long
is unknown) as well. "
Does the first dose always generate antibodies?
Or could this not happen?
“It is not normal, but it
happens in 10-20% of those vaccinated
for Covid.
We saw it with Sputnik and it is published in the works that evaluate AstraZeneca.
With Sinopharm it is similar, although nothing was published from phase 3 ”, says Docena.
The amount of antibodies that can be acquired with the first dose is highly variable and depends on the genetics of each organism.
"Not all of them produce the same quantity with the vaccine, some do not even generate them with the first dose and only acquire them with the second, which is when 100% of those vaccinated produce antibodies and in quantity. There the individual heterogeneity is diluted" , expand.
And he clarifies that the other cellular mechanisms that are induced with the vaccine must also be considered.
In the same vein, Regazzoni points out: “The amount of antibody potency generated by the vaccine
depends on design factors and who receives it
.
For this reason, in some people the vaccination will have been effective to prevent infection, in others it may be that it prevents only serious forms and in a different group, it does not work and the body is susceptible to being infected with the virus as if it had not been vaccinated ".
Stryjewski emphasizes that the majority,
90%, acquire antibodies
(humoral immunity) with the capacity to neutralize the virus, but that approximately a quarter no longer have them within six months.
“
Losing the antibodies does not necessarily mean losing immunity
, since upon re-exposure they could quickly produce them again and / or be defended by trained T cells (cellular immunity) that are not measured in practice.
For this reason, the marker used today to quickly understand if there is immunity or not are antibodies, "he explains.
With a single dose, it is the percentage that these antibodies are lost in a significant percentage of patients within six months, with which the protection of the vaccine could be lost or diminished more quickly than if the two-dose schedule is administered.
"In other words, a dose would reduce the clinical disease in the short or medium term, although
it would not be the best long-term strategy to stop the transmission of the virus,
" warns the head of Hospitalization at CEMIC.
Cell memory
The specialists consulted understand that every vaccine induces cellular memory (generated by T lymphocytes, responsible for cell-mediated immune mechanisms) and humoral (B lymphocytes, responsible for generating antibody-mediated immune mechanisms).
This memory is responsible for maintaining the immune response over time.
In this sense, Daniela Hozbor, an expert in vaccines and researcher at Conicet, remarks that “the first dose is not safe.
Reduces viral load and produces cellular response.
The antibody level doesn't mean anything in terms of how much I'm protected.
It is necessary to observe the correlate of protection that would involve the neutralizing antibodies and also a cellular response ”.
The infectologist Pablo Bonvehi refers that the studies of the different vaccines show that the antibodies begin to rise after 10 to 14 days after the first dose, but that due to their own dynamics it is not expected that they decrease abruptly, but rather slowly over time. Over the weeks: "Even though the antibodies are decreasing, the person already has an immunological memory, which generates a very rapid response after the virus encounters and this will surely provide protection."
For its part, Docena points out that "with other vaccines, memory can last for years and in fact it is inoculated only once in life for many of them, but
when we talk about Covid it is not known how long the acquired immunity lasts for sure
" .
However, Geefner indicates that “in 80% of infected patients a memory response mediated by B lymphocytes is observed, which is expressed in the production of antibodies and lasts for at least nine months.
The T cell-mediated memory response appears to persist for longer periods of time. "
ACE
Look also
Flu vaccine: when to give it now that the second dose of the Covid is delayed
Second wave of coronavirus: the two variables that the Government looks at and the change in the testing strategy
