Why are two doses of the vaccine taken? And when, on the other hand, can only one be enough? Can the second dose be given with a different vaccine? Within a year, scientific research has led to the creation of four extremely effective vaccines that are changing the history of Covid-19 for the better. However, not all vaccination strategies are the same. With the passage of time and the accumulation of data, the world of science is further refining the weapons that will allow us to get out of the pandemic state. But let’s start with the most current question, after the AstraZeneca case and the suspension by the health authorities of inoculation under the age of 60 (in Italy, in other countries the limit is not the same). What to do with who got the first dose of the Oxford vaccine? Do the second or change the vaccine?
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Could the second dose be different from the first?
Currently it is not possible to make the mix and match – this is the technical term – of vaccines. Once the cycle is started with one, it must be finished with the same vaccine. However, vaccination strategies based on the use of different vaccines between first and second doses are being tested. In England, for example, the University of Oxford is evaluating the validity of this approach through the alternative combination of first and second doses of Pfizer-BioNTech and AstraZeneca’s vaccine. Not only that, the latter – in some countries where Sputnik V is already approved – is being tested with the Russian vaccine. A strategy aimed at understanding whether the mix of different products is able to induce an even more efficient immune response and protect against any variants. An idea that has its roots, as far as Sars-Cov-2 is concerned, in a promising study carried out on an animal model. However, a strategy still to be explored. Germany, however, has decided to proceed with the second dose of Pfizer or Moderna vaccine for those who have been vaccinated with AstraZeneca and are under 60.
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How do coronavirus vaccines work?
The goal of any vaccine is to stimulate the immune system to recognize a portion of the infectious agent so that if the real one is encountered, antibodies and T cells can neutralize it. For Sars-Cov-2 all the vaccines on the market and the experiments are based on the recognition of a portion of the “spike”, the surface protein that allows the virus to interact with our cells and penetrate inside to replicate. Stimulated the production of antibodies against the spike protein, in case of contact with the virus our body will be able to neutralize the infectious agent.
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How many types are there?
To date, the vaccines approved in our country against Sars-Cov-2 belong to two categories: mRNA vaccines and viral vector vaccines. In both cases, the immune system is stimulated to produce antibodies against the spike protein. The first two are the vaccines developed by Pfizer-BioNTech and Moderna. The second two from AstraZeneca and Janssen, with Johnson & Johnson. Unlike vaccines known to date – which stimulate the immune response by exploiting attenuated, inactivated viruses or protein fractions of them – both those with mRNA and those with a viral vector have the characteristic of containing the information necessary to make our cells produce the protein spike.
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In those with mRNA the vaccine consists in providing the cells with all the necessary information in the form of mRNA. The information is conveyed inside a lipid “capsule”. Once assembled and expelled from the cell, the protein is recognized by the immune system, giving rise to the production of antibodies capable of recognizing the virus. In those with a viral vector, the information is contained in the form of DNA which is then transcribed into mRNA and then “translated” to give life to the “spike”. In this case, the information is conveyed inside the cell through a harmless virus for humans that acts as a carrier.
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How Effective Are Vaccines?
All vaccines available today in our country are effective in avoiding the severe form of Covid-19. Having clarified this aspect, the different vaccines have a different efficacy in preventing the development of the symptoms of the disease. THE mRNA vaccines, in the clinical trials that led to their approval, showed an efficacy of 94.1% (mRNA-1273 from Moderna) and 95% (Comirnaty from Pfizer-BioNTech) in reducing cases of symptomatic disease. According to the data collected from the millions of administrations carried out to date, the overall effectiveness has been around 90%. According to the data available to date, mRNA vaccines have also proved effective in blocking the transmission of the infection.
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As for Vaxzevria, the AstraZeneca vaccine, the effectiveness after the first dose is 76%. After the second dose, 12 weeks after the first injection, 84% is reached. Important results, published on The Lancet, which were then confirmed in large-scale administrations and which showed how effective it is also in the population over 55 years. The situation is different with regard to the vaccine developed by Janssen (Johnson & Johnson). Unlike the other 3 vaccines approved today in Italy, Janssen’s requires a single administration. According to the data analyzed by Ema – which led to the approval of the vaccine throughout the EU – resulting from the Ensemble clinical trial, the vaccine has been shown to be effective in reducing symptomatic cases of Covid-19 by 67% two weeks after administration. . Effectiveness that reaches 85% in the prevention of severe forms of the disease. However, this vaccine was stopped by the American FDA in the US following six cases of rare thrombosis (out of about 7 million doses in the US) found in women who had received immunization.
Do viral variants knock out currently available vaccines?
A loss of efficacy due to the presence of viral variants not recognized by the antibodies generated with the vaccine would mean leaving room for the virus again. At the moment, however, this does not seem to be happening. This is primarily due to the “polyclonal” response of our immune system. When the body comes into contact with SARS-Cov-2 – or with a portion of the spike protein in case of vaccination – the defense cells begin to produce different antibodies, each capable of recognizing different portions of the spike protein. According to the most recent studies, at least 5-6 areas of the spike protein could be attacked by the various antibodies. And it is for this reason that some mutations would not be able to modify the characteristics of the protein to such an extent that it is no longer recognized.
To date, all vaccines are effective against the English variant, the viral form that has taken over in our country and beyond. As for the other variants monitored for some time, the South African and Brazilian ones, as published on the pages of the New England Journal of Medicine, are able to be neutralized by mRNA vaccines. While decreasing the ability to recognize part of the virus, a reduced neutralizing capacity does not mean a loss of efficacy. Different speech for viral vector vaccines against the South African variant. For the first, Vaxzevria has not been shown to be useful in mild / moderate forms of the disease. Janssen instead saw a reduction in effectiveness to 64%.
Good news also comes from people who have already been positive for the virus. In a study recently published on the New England Journal of Medicine a single dose of Comirnaty has been shown to be useful in producing antibodies against the South African and Brazilian variant.
How many doses are needed?
All vaccines approved today, except Janssen’s, have two doses. It is only through the complete cycle that maximum effectiveness is achieved. Those with mRNA with a distance of at least 21 days from the first dose for Pfizer-BioNTech and 28 for Moderna. This interval can be extended up to 42 days. For the AstraZeneca vaccine, the second dose can be given 4 to 12 weeks after the first.
How long does the vaccination take effect?
Several days pass from the moment of injection to the production of antibodies against the spike protein. For mRNA vaccines, protection begins two weeks after the first dose and reaches its maximum one week after the second dose. For the AstraZeneca viral vector vaccine, protection begins approximately 3 weeks after the administration of the first dose of Vaxzevria. Protection which becomes maximum 15 days after the administration of the second dose.
What happens if those who have been positive for Covid-19 get vaccinated?
For those who have developed the disease, regardless of the severity of the symptoms developed, the vaccine will be carried out in a single dose, considered a booster as the person has already “immunized” by coming into contact with the actual virus. However, vaccination must be performed at least three months after the infection and preferably within six months of the infection. An indication valid for all people infected during the second wave of the pandemic but not for those who fell ill between February and May last year.
