A single dose of RNA vaccine would be sufficient for people who have already passed COVID. This is the conclusion of a study published a few days ago in The New England Journal of Medicine, which shows that people who have already suffered from the infection and therefore had previous immunity, respond the same or better to a first dose of mRNA vaccine. than people who have not had the disease and receive both doses.
Undoubtedly, very encouraging news that will greatly simplify vaccination campaigns but which, as the researcher at the Institute of Philosophy of the CSIC and expert in immunology Matilde Cañelles reminds us, “ only applies to RNA vaccines, for which cannot be extrapolated to the AstraZeneca vaccine , which is already applied in Spain, nor to the Janssen vaccine, which is ready to be approved in Europe ”. Therefore, the question of whether one dose of vaccine is sufficient if you already have previous immunity to COVID-19 must be qualified: if we refer to adenovirus vaccines such as AstraZeneca’s, it is necessary to receive both doses, since it is not yet we have that information for these types of drugs.
Should the doses be more spaced?
With regard to the convenience of spacing the doses of the vaccine, the type of drug to which we are referring must, again, be qualified. “In the clinical trials of mRNA vaccines (Moderna and Pfizer) the guideline of spacing the doses 3-4 weeks was followed, and usually they are not departing from this norm, because there is no information on what happens if they are spaced , in addition to the fact that they are being administered to people over 65 years of age, who take longer to develop an immune response and therefore may be more unprotected until receiving the second dose ”, the expert explains.
On the other hand, in the clinical trials of the AstraZeneca vaccine, it was tried to space the doses more and it was found that in some cases this procedure was even more effective. For this reason, in Spain the intention is to apply the second dose of this drug around 10-12 weeks later, a measure that may also be convenient in the current context of supply shortages.
Is the UK right to give just one dose?
The United Kingdom procedure is controversial, since here we are not talking about administering single doses to people who have previously had COVID, nor about spacing them more in time, but directly about applying only one dose in order to immunize as many as possible. of people possible in less time. “In my opinion, this is a somewhat daring bet, like many of the decisions taken by the United Kingdom during the pandemic and which generally contradict scientific information,” reflects Cañelles. Imagine that you receive a million doses and, instead of vaccinating 500,000 and reserving the other half for the second dose, you vaccinate a million people. In the short term you will notice an improvement in the statistics of infected, but the problem is that you are giving these people suboptimal protection. And this type of protection is precisely what is used in laboratories to artificially create new variants of viruses. “
As the researcher explains, it has been shown that new variants arise when the virus is seen in a situation in which there are certain barriers to its expansion, but they do not completely stop it. “This is clearly seen in the moments in which new variants of SARS-CoV-2 have begun to emerge: after applying the first drastic measures of confinement and social distance, when there were already large pockets of population that had already passed the disease and had partial protection, etc. ”, indicates the researcher. “And, therefore, by putting just one dose, you are playing with fire, because perhaps you are empowering that there are many partially unprotected people. And this could favor the emergence of new variants capable of evading the immune response caused by the vaccine ”.
“As an immunologist, I would never recommend putting just one dose, except in the case of people who have had COVID-19 in the last six months, which is the minimum time that we know that immunity lasts,” agrees Carmen Álvarez-Domínguez, Professor and researcher in Immunology at the International University of La Rioja (UNIR).
Vaccine effectiveness against new variants
“Little by little, some very encouraging data is being published,” Cañelles explains. “For example, a preliminary study suggests that the Pfizer vaccine would continue to be useful for the British, South African and Brazilian variants. And Moderna has already developed a version of its vaccine that seems to work against the South African variant, they are already doing trials with people who had received the first two doses ”.
“The good thing is that the type of technology that mRNA vaccines carry allows them to be readapted quickly: if a vaccine does not work for a variant, one can quickly develop one that does and put another booster dose , with traditional vaccines it is not possible. it could change like that, ”says Álvarez-Domínguez. “New variants will continue to emerge, but there is still a huge amount of virus circulating in the world, so it is necessary that vaccination campaigns go as quickly as possible.”
First of all, caution
A few days ago, the US Centers for Disease Control and Prevention (CDC) published a guide of recommendations for people considered fully immunized against COVID. For the first time, restrictive measures would be eased somewhat for this population group. “The first studies have already been mentioned that would indicate that RNA vaccines are capable of stopping transmission, up to 90% in vaccinated people,” Cañelles explains. “But all this causes me concern, because we are talking only about one type of vaccine. At present, we do not know if adenovirus vaccines are also capable of slowing down transmission – that is, a vaccinated person is less likely to develop a serious infection, but we do not know if they are still capable of transmitting the virus if they become infected properly. asymptomatic-. In Spain, precisely, we are vaccinating people over 65 years of age with RNA vaccines, and young people, with greater mobility, with vaccines that we still do not know if they cut transmission. Relaxing the measures seems premature to me ”, reflects the researcher.
A position in which Álvarez-Domínguez agrees: “what we have to do is get vaccinated and maintain security measures. If we want to avoid future waves we must totally avoid risk situations ”.
