These days, thousands of people are receiving the booster dose of the vaccine. Why is it necessary? When is immunization effective? How long does it last? Is a vaccinated person immune to any strain? Is immunity more effective depending on the type of person receiving the vaccine? This is what we know so far.
Why is double doses of current COVID-19 vaccines needed?
To explain, let’s start at the beginning. The immune response to COVID-19 vaccines begins when we are inoculated with the antigen of the pathogen. That is, a small part of the virus that is not dangerous, and that has been shown to induce an immune response similar to that produced by the infectious agent, but without causing the disease.
After injection, the cells of the first line of immune defense respond by producing antibodies and memory T cells. If in the future they meet the pathogen again, the antibodies will be able to block it, while the T cells will destroy the cells in our body that they have infected.
This initial response develops between 7 and 14 days after receiving the first dose of the COVID-19 vaccine. After that time, it returns to its starting point. And that’s when you can re-inoculate a second dose of antigen and generate another wave of memory cells that amplify the first response.
When is immunization effective?
Not all vaccines require double doses to generate a powerful and wide-ranging immune response. It only happens to vaccines based on small antigens, but not to those designed from inactivated whole pathogens. This is the case with Pfizer and Moderna vaccines, based on RNA, which is a fairly tiny molecule.
Taking into account the waiting time between the first and the second dose, it will take almost a month and a half before considering someone correctly vaccinated against COVID-19.
How long is immunization with a vaccine? Is it suitable for all strains?
Although it is variable and depends on each antigen, what has been observed in clinical trials with COVID-19 vaccines is that the immune response lasts between four and six months. It may even last considerably longer.
Once vaccinated, will our immune system recognize any variant or strain of the SARS-CoV-2 virus if we become infected? Since the memory response is made up of two types of cells, and these cells recognize the virus antigen somewhat differently, it is not easy for a new variant to affect both cell types at the same time. In other words, if a variant affected the ability of some memory T cells to recognize it, we would still have a wide repertoire of antibodies that could neutralize the virus. And the same if it is the other way around.
In addition, fortunately the technology of RNA vaccines allows them to be modified quickly and easily adapted to new variants. In short, it seems that we will always have vaccines that are effective against new strains.
What factors influence the immune response to vaccines?
To begin with, it depends on the age. The immune response also ages, and that means that both antibody-producing T cells and B cells respond worse in older people. This is what in the jargon is called immune senescence.
Genetics are not indifferent either. The response to vaccines can be impaired by genetic deficiencies that affect the cells of the immune system or the production of substances that regulate the inflammatory response and the function of the immune system, including cytokines.
Regarding gender, various studies suggest that vaccines are more effective in protecting women from tetanus, flu and other infectious diseases.
To this we must add other factors, such as silent infections that we may have without knowing it when vaccinating. Or be subjected to treatments with antibiotics and other drugs when we are going to inoculate ourselves.
There is even evidence that our diet, alcohol consumption, physical exercise or stress condition the response to vaccination.
Finally, any physical condition that lowers our immune status, be it a disease or a non-pathological condition such as pregnancy, could reduce the response to vaccines.
What happens once we have been vaccinated? Can we relax in the face of the virus?
The answer is a definit no. A vaccine is by no means a drug that kills the virus. It only prevents infection or reduces the severity of the disease. Do not forget that individual vaccination will not make the virus disappear. Only when a large percentage of the population is vaccinated will we have good global immunity against COVID-19.
In addition, it is still too early to know if vaccination has an effect on the transmission of the virus. We will have to wait for a large number of the population to be vaccinated before it can be determined. Until then, the best support we can give to the vaccination campaign is to continue applying the measures of masks, social distance and avoiding risky situations.
Carmen Álvarez Domínguez, Biochemist and molecular biologist, immunologist, expert in vaccines and professor of research in Sanitary Processes at the Faculty of Education, UNIR – International University of La Rioja
This article was originally published on The Conversation. Read the original.
