- Guillermo López Lluch
- The Conversation*
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3 hours
Image source, Getty Images
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A recent study indicates that even with mild symptoms, those reinfected can be a source of spread of the virus.
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As the number of people vaccinated increases, the feeling of freedom grows and we relax. Some governments already establish measures to give carte blanche to the mobility of vaccinated people without limitations. But are we sure that mobility can be opened without having achieved group immunity?
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Vaccination, like contagion, immunizes the affected person, who, generally, will not suffer symptoms or these will be mild in future reinfections. But that does not mean that the virus will go away. It can even spread again.
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The key is in the activity of the immune system and the proliferation capacity of the virus in these people.
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A trained immune system clears the virus before it can cause serious damage to the body.
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Therefore, the question to be cleared now is whether immunized people maintain contagion capacity. The answer will depend on the amount of virus they can spread.
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Symptoms less seriouss or asymptomatic
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A recent study carried out in senior centers in Chicago showed that 4.2%, among workers and patients, were infected with SARS-CoV-2 in a period of four months (December 2020-March 2021).
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Image source, Getty
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Cytotoxic T lymphocytes act against cells that are expressing the virus protein (pictured).
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Of those infected, most had not been vaccinated. But 6% of the infections had occurred in fully vaccinated peopleas and 23% in which they had received single dose.
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On the other hand, reinfections of people who have had the disease are rare but do occur.
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In a study carried out in the United Kingdom with health workers who had suffered COVID-19, 0.6% suffered reinfection. Of course, with mild symptoms.
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In addition, the recent SIREN study (SARS-COV2 Immunity and Reinfection Evaluation, carried out by the British public health system) focused on immunity and reinfection by SARS-CoV-2 concludes that the immune response largely prevents the risk of contagion.
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But it also indicates that, even with mild symptoms, those reinfected can be a source of spread of the virus.
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In the United States, exposure to the new variants has been considered as a factor against possible reinfection in already immunized people.
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As for Spain, there have already been reported cases of fully vaccinated people who have been reinfected presenting mild symptoms accompanied by high viral loads. The same has happened in other countries such as Singapore or the Seychelles.
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Antibodies are not everything: the relevant role of T lymphocytes
Throughout the pandemic, much attention has been paid to the levels of antibodies and how long they remain in our blood. But are antibodies really that relevant?
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Image source, PEDRO PARDO/AFP via Getty Images
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This group was immunized with the Pfizer-BioNTech vaccine in Mexico City.
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Antibodies are produced by activated B lymphocytes that transform into plasma cells. Plasma cells stop working over time and die.
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The antibodies produced by these remain circulating in the blood for weeks or months until they degenerate and are eliminated.
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Memory B lymphocytes are also produced that will act more quickly and generate plasma cells and antibodies more quickly and efficiently in the event of reinfections. Therefore, the duration of the antibodies in the plasma is not so important: it’s the memory cells that matter.
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T helper lymphocytes are also activated in the immunization process. These are cells responsible for controlling the activity of the immune system.
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Simultaneously, cytotoxic T lymphocytes come into play, which act against the cells that are expressing the virus protein and eliminate them, thus reducing the proliferation of the virus.
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In both types of lymphocytes, memory cells are generated with the ability to rapidly activate in reinfections.
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T lymphocytes are also essential against virus infections by releasing interferon, a signaling protein that blocks virus replication.
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The SARS-CoV-2 mutations are especially affecting protein S. Those variants that present a change in this protein that improves its binding capacity to human protein, increase its infective capacity.
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For this reason, the variants that are being imposed around the world are presenting similar changes.
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Does it mean that vaccines lose effectiveness? Vaccines generate antibodies against different areas of protein S.
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They also activate helper and cytotoxic T lymphocytes that act by recognizing different areas of the protein.
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Therefore, the point mutations that are taking place in the protein S of the virus they do not have to affect the immune response in an important way.
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Immunization only protects the immunized person
The vaccine does not totally prevent the virus from invading. Both antibodies and lymphocytes “prepared to defend ourselves” are found within our body.
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Image source, Getty Images
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Vaccination, like contagion, immunizes the affected person, who, generally, will not suffer symptoms or these will be mild in future reinfections.
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The virus infects us mainly through aerosols in the air, so it begins by invading the cells that line the upper part of the respiratory system.
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This implies a relationship between the ability to infect and the reaction time of the immune system.
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Immunized people have a trained system that will act in a short time. But while, the virus can proliferate and the person would be infected but without symptoms. And you can infect others.
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The simple fact that the virus encounter opposition from the immune system almost immediately It allows us to think that there will be a reduction in its transmission capacity. In fact, a recent study in the UK (without peer review) indicates that up to 50% less.
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Since immunization increases the number of asymptomatic people who do not know they are infected, we cannot lower our guard. Therefore, the European Center for Disease Prevention and Control (ECDC) warns about infections from immunized people.
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It is essential that group immunity is achieved to reduce the spread of the virus and infections.
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*Guillermo López Lluch is a professor in the area of Cell Biology. Associate researcher at the Andalusian Center for Developmental Biology. Researcher in metabolism, aging and immune systems and antioxidants. Pablo de Olavide University.
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