Questions about COVID-19 vaccine boosters have dominated scientific discussions, news headlines, and casual conversations recently, but the practice of giving our immune system regular “updates” is anything but new. In an interview with The Harvard Gazette, Jonathan Abraham, assistant professor of microbiology at the Blavatnik Institute at Harvard Medical School and specialist in infectious diseases of the Brigham and Women’s Hospital, talked about the science and history of vaccine boosters.
“Studies show that After being vaccinated against the coronavirus, protection against SARS-CoV-2 and the ability to prevent infection by new variants are reduced over time. Data from clinical trials revealed that a booster dose of Pfizer-BioNTech COVID-19 vaccine is effective in protecting against COVID-19, adding to other evidence showing that a booster dose can be much more effective compared to the main vaccination schedule ”, warn the Centers for Disease Control and Prevention (CDC).
But what exactly is a booster shot and how does it work? “A booster shot It is intended to increase immune response levels after they have naturally decreased. A booster tricks the immune system into thinking it is seeing a pathogen again, so the antibody-producing cells and other immune cells are activated. The quantity and quality of antibodies that are produced can be increased. Through a process called By antibody affinity maturation, our immune system learns to do a better job of recognizing a pathogen and producing antibodies that bind more closely to its target. For the SARS-CoV-2 virus, for example, affinity-matured antibodies may be more efficient in recognizing variants with multiple mutations, “said the specialist.
After having received the complete schedule of vaccines against the COVID-19, the third application of a vaccine can occur for different reasons. That is why they are called additional or booster dose and the reasons that motivate its application are different.
Is a booster shot the same that some patients need because they are suffering from a certain disease or that they are immunocompromised, than the third dose or also called additional dose? The answer is no. Each of these vaccines is given at different times than the second dose and not in just any patient.
Several people have been called in for a third dose within four to six weeks of the second dose. and this is where the confusion that occurs with the third dose that is applied six months after the second is generated. “Confusion is generated because the third dose should be given 6 months after the second dose for all vaccines and 5 months for the Sinopharm vaccine.”, Explained the renowned Argentine pediatric pathologist Marta Cohen, in relation to the third dose.
“There is another dose, than the additional dose that World Health Organization (WHO), the British government and several countries apply it, which they have recommended for those countries that have severe forms of immunodeficiency. This dose, which we can call an additional dose, which It is part of the primary vaccination scheme, it is recommended that it be applied at 8 weeks, that is, a few months after the second dose. But not for everyone. It is for specific cases which is analyzed by the general practitioner of these patients ”, explained Cohen.
The Extra dose serves to raise the immune response in people with immunodeficiency or with immune changes naturally associated with aging (immunosenescence). It also serves to reduce the impact of mortality due to COVID-19 in those over 50 and before the advance of the variant Delta in community broadcasting. Following international recommendations and some clinical studies conducted in the country, the The National Immunization Commission (Conain) advised the Ministry of Health of the Nation in the decision to add one more dose to the homologous or combined schemes in those two groups, following some stipulated parameters.
Consulted on the need for periodic reinforcements in the foreseeable future, Abraham argued that “vaccines are still extremely effective in preventing serious infections and death, but they are not 100% effective in stopping the acquisition and transmission of the virus. Particularly in areas with high infection rates due to low absorption of the vaccine, vaccinated people are more likely to be exposed to the virus and contract a breakthrough infection. With this in mind, I would speculate that due to the highly transmissible variants, we will need periodic boosts for years to come. During that period of time, the use of an updated vaccine strain may be prudent because it is unlikely that we will ever see the original vaccine strain again, as it is practically extinct. “
However, according to the expert, it would not be the first vaccine requiring periodic reinforcements. “It is recommended that children and tweens receive five doses of the vaccineto DTaP and a Tdap booster shot as the best way to protect yourself against whooping cough. We generally require boosters, with a Td or Tdap component, every 10 years to preserve immunity. For some pathogens, having pre-existing and prepared immune responses, for example, in the form of measurable antibody levels, is critical for efficacy. Then, as antibody levels naturally decline over time, a boost is required ”, detailed.
And continued: “For other pathogens, What the hepatitis B virus, completing the series of three immunization injections is likely to provide lifelong protection, so measurable antibody levels are not routinely monitored. But, if the risk of infection is higher, for example, for healthcare workers, it may be important to check antibody levels at least once and give a booster if the antibodies are found to be low. Then, the decision to promote or not to promote is multifactorial and, ultimately, is based on studies and experience ”.
For now, the same SARS-CoV-2 peak protein antigen is used for the vaccine and boosters. Nevertheless, there is a possibility that, over time, the SARS-CoV-2 spike protein will change shape or mutate enough to require a boost with an updated strain antigen to prepare the immune system to recognize the mutant virus. “This scenario would be more similar to what is done with seasonal influenza virus vaccines each year, although we think more of influenza vaccines as equal-strain vaccines rather than periodic boosters,” he concluded. Jonathan Abraham, Harvard Medical School and specialist in infectious diseases of the Brigham and Women’s Hospital.