Covid-19 vaccines: an understandable comparison




But what is the most convenient vaccine? Are there better vaccines than others? Why do they have different prices and different storage requirements? Single or multiple doses?

We will better answer these questions if we understand what a vaccine is and how they differ from one another.

What is a vaccine?

According to WHO, a vaccine is any preparation designed to generate immunity against a disease by stimulating the production of antibodies.

Immunity is acquired after an infection. For this reason, vaccines (punctured or inhaled) must trick our body by simulating an infection by the pathogenic microorganism (virus or bacteria) against which they seek to immunize us and putting the defensive system on alert. Thus, when we actually contact the unwanted microorganisms, our plasma cells (B lymphocytes) will have produced antibodies that will be waiting for them, specifically neutralizing them and preventing us from getting sick.

Since science has developed various strategies for pretending an infection, there are different types of vaccines.

For tastes, vaccines

Live attenuated vaccines. They are live virus suspensions that produce a real infection and induce a long-lasting and effective response. As viruses are previously weakened, the infection comes in a light version. These are perfect vaccines for adults (because they are cheap and single-dose). However, they can be dangerous for the immunosuppressed (including the elderly and people with serious pathologies), who can unleash the infection in all its glory. As this virus is new and, today, there is no definitive medicine against it, we cannot take risks. For this reason, there are no trials for SARS-CoV-2 of this type of vaccine (where measles or rubella are found).

Inactivated vaccines. Similar to the previous ones but with dead viruses, so we minimize risks (by not being able to reproduce). In return, the immunity generated is lower and lasts for less time. So when we get vaccinated against rabies or hepatitis A, we need “booster doses”. An even safer modality, the so-called recombinant, polysaccharide and combined subunits, do not work with complete viruses, but with inactivated “bits” of viruses with strong antigenic capacity. They are the ones that immunize us against hepatitis B or papillomavirus. Since our immune system mistakes those bits for whole viruses, it develops a strong response. However, as in the previous case, booster doses are required.

Inactivated vaccines are the Chinese ones from Coronavac (Sinovac) and Sinopharm, which have the advantage of being able to be kept and transported in conventional refrigerators.

Toxoids. When it is not the microorganism that causes the disease, but the toxin that it produces, the vaccine is created by deactivating the toxin and achieving immunity against it (not against the microorganism). This occurs only with some bacteria, such as those responsible for tetanus or diphtheria. As SARS-CoV-2 is a virus and does not generate toxins, there are no vaccine trials of this type.

Recombinant vector. This type of vaccine represents a substantial advance in biological engineering. It consists of inoculating a good virus, which is called a vector. The vector carries inside, instead of its original RNA, one modified to synthesize proteins of the bad virus. When the virus enters our interior, it does not cause us disease (because it is good) but it induces immunity against the bad virus (because it expresses its proteins). This is how smallpox was eradicated from our planet in 1980 (one of the great biomedical achievements of science). Of this type, in its non-replicating modality, are the AZD1122 vaccines (University of Oxford / AstraZeneca), the Chinese CanSinoBIO from Petrovax, the British Ad26.COV2.S from Johnson & Johnson and the Russian Gam-COVID-Vac or Sputnik V , with which the Russian population will be vaccinated imminently).

Again, two doses are needed.

DNA vaccine. It consists of the direct injection of DNA through a plasmid or an expression vector. This DNA encodes an antigenic protein of interest, which will induce the activation of the immune system. As our virus has RNA (and not DNA), vaccines of this type are not being tested.

Messenger RNA (mRNA) vaccine. It is the latest in biotech vaccine. We do not inoculate the antigen to trigger the immune response. Instead, we enslave living cells in the laboratory, make them produce most of the immune response for us (as if they were our B lymphocytes), and directly prick millions of mRNA (the blueprint for making antibodies).

But… oh problem! We have RNase enzymes that will destroy them. Moreover, we have them, in addition to our internal environment, on our skin or in our own breath, with which the risk of destroying the mRNA before it fulfills its role is very high. To avoid this, a protective lipid envelope is built and a lacasito is made, where the chocolate is millions of molecules of the precious mRNA. It is a complex technology that has involved a very strong investment in research, which is why these vaccines are the most expensive.

The mRNA-1273 vaccines from Moderna (North American) and BNT162b2, from North American Pfizer and German BioNtech, are based on this ingenious idea. As the wrapper of the lacasito is very labile, it will need a lot of cold for its conservation and transport (-20ºC and -80º, respectively). This small inconvenience guarantees a safe, effective (95%) and very fast immunization. Boris Johnson has just announced the start of mass vaccination of the British population with vials from Pfizer.

The vaccines mentioned are those that are in the most advanced phase of clinical trials (phase III) or have already requested approval from the EMA (European Medicines Agency), although many more are under development, some of them Spanish.

Any vaccine marketed in Europe must meet the EMA requirements. This is not the time for political pressure, much less economic pressure. The rigor that characterizes the work of this agency must be, now more than ever, its only modus operandi. In your hands is the enormous responsibility of ensuring the safety of all Europeans in the most important health crisis in their history.

Article published in THE CONVERSATION.ES

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