What is the best time to get a flu shot?

For most people, the flu is nothing more than a respiratory infection as odious as it is temporary, but in some cases it can become a serious illness that can be fatal. What is clear to everyone is that the best way to prevent the effects of the disease, in oneself and in others, is in the form of a vaccine . That is why the health authorities promote the vaccination campaign that begins today in Madrid every autumn and that this week will also begin in other territories. The flu vaccine is safe and effective, but it does not always reach the same levels of protection, and the reasons for this variability could be the time of day it is administered.

At least, this is what can be deduced from an investigation that has come to light this month in the journal Proceedings of the National Academy of Sciences. The study was done with mice and the flu vaccine was not used, but the article concludes that the response of the cells of the immune system to immunization generally increases at that time. And the cells the scientists studied were CD8 T lymphocytes, the same type that protect against influenza viruses.To reach this conclusion, the scientists divided the rodents into two groups, each of which received the immunization at different times of the day. After one week, the spleen of the animals vaccinated at noon contained twice as many CD8 T lymphocytes, which are cells that have mechanisms to attack any other cell in the body that expresses a fragment of foreign antigen. Its role is important, especially in viral infections.

Although the conclusions of the work cannot simply be applied to influenza vaccination, if the protection against this disease also increased in case of applying the vaccine at noon, a simple adjustment in the schedule of its administration could achieve a better response from Antibodies to this disease, which causes between 250,000 and 500,000 deaths worldwide each year, according to the World Health Organization. The idea makes sense, depending on how chronobiology works.

Take advantage of the moment of greatest sensitivity

“In the light of knowledge, we must assume that any organism is a system that changes in its responses throughout the day, following cyclical patterns, recurring every 24 hours, called circadian rhythms. The immune system, made up of cells responsible for defending against pathogens and tumors, is no stranger to these rhythms, “ explains Juan Antonio Madrid Pérez, professor of Physiology and researcher at the Chronobiology laboratory at the University of Murcia.

According to Madrid, a biological clock of T lymphocytes controls the proliferative and antibody-generating response of these cells when an antigen enters the body, such as that inoculated in the vaccination process “At certain times of the day, the lymphocyte circadian clock makes them especially sensitive to antigenic stimuli, while at others their sensitivity is minimal.”

Knowing what these moments of maximum sensitivity are, Madrid considers that the effectiveness of a given vaccine could be increased because, against influenza viruses, these immune cells exert a protective effect. Those with the highest rates of CD8 T lymphocytes are the most resistant to the viruses that cause the disease, while those with the lowest values ​​suffer the disease most severely. So would it be advisable to schedule the vaccine in the morning?

More studies point to morning vaccination

The idea that the flu shot could be more or less effective depending on the time it is given is not new. Researchers from the University of Birmingham, UK, have already advised this in a study published in 2016 in the journal Vaccine , after observing that protection was only effective in 40% of people over 65 years of age. Its author Anna Phillips explained it like this: “The results show that morning vaccinations offer a more efficient response, which will not only help in the development of vaccination campaigns against influenza, but could be an important aspect to improve vaccination strategies in general “.

His research involved 267 British citizens over the age of 65, who received the vaccine against three strains of the influenza virus between 2011 and 2013 in the morning – between 9.00 and 11.00 – or in the afternoon –Between 15:00 and 17:00. For two of the virus strains, people who received the vaccine early in the morning had a significantly higher level of influenza antibodies within 30 days of inoculation. No differences were observed in the case of the third of the strains, so the efficacy of the vaccine was similar regardless of whether it was received in the morning or in the afternoon.

The new research has yet to be replicated in humans to see if it would really be wise to vaccinate patients at a precise time of day, but if confirmed, its authors argue that the benefits would be greater than increasing the efficacy of existing vaccines. According to them, we would be at the door of new therapies based on T cells based on the time of administration. “As with vaccines, our body shows daily rhythms, both in the curative or therapeutic effects of drugs and in their unwanted or toxic effects. The interesting thing is that the therapeutic and toxic rhythms are not coincident, so you know those rhythms can increase the effectiveness of many treatments pharmacological “adds Madrid.

An open door to better treatments

The daily cycle of the immune system affects the origin and severity of some ailments and their symptoms. “If we understood better that relationship between the time of day and the activity of defense cells, we could optimize the immune system to recover before an illness, or administer treatments at a specific time to improve its effectiveness, or avoid side effects, such as in the case of vaccines or chemotherapy, “ says immunologist Christoph Scheiermann, from the University of Geneva (Switzerland) and co-author of an article published in the journal Trends in Immunology that reviews scientific studies on this issue.

Treatments like those of high blood pressure, asthma and certain types of cancer are already benefiting from these chronobiological applications. “The rates of activity of a drug,” says Madrid, “depend on many factors, such as rates of absorption, binding to plasma proteins, metabolism, excretion, and cellular receptors for the drug.” In cancer, however, it is more complex, since most of the drugs used have a half-life in the human body of more than 24 hours.

According to this professor, the biological clock and the science that studies it, chronobiology, is one of the basic pillars, along with nutrition and physical exercise, for the maintenance of health.Life evolved over millions of years under a cyclical environment where the sun was the main source of light. However, in the last century, life in developed countries began to change rapidly and three coinciding trends emerged with a significant impact on society and health. “Food has become abundant and food intake has shifted towards the end of the day; sleep time has gradually decreased along with an increase in irregular patterns, and exposure to light at night has increased, inhibiting the secretion of melatonin, a hormone with antioxidant, sleep-inducing and anti-tumor effects. ”

These alterations, says the professor of Physiology, particularly relevant for sensitive populations such as children, young people, shift workers and the elderly, lead to disorganization of the circadian system or chronodisruption and, as a consequence, to a greater incidence and aggravation of numerous pathologies ( cognitive disorders, depression, diabetes, hypertension, insomnia, cancer, accelerated aging and immunosuppression).


by Abdullah Sam
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