“They quickly respond by making more clones of themselves, so they start to fight back.” Memory cells “are quickly recruited to the site of infection,” Iwasaki explained. White blood cells called memory T and B cells stand guard for years, ready to mount a defense, including generating antibodies, against a particular antigen should it ever appear or reappear. “Luckily, the immune system has multiple layers of protection,” Akiko Iwasaki, PhD, an immunobiologist at the Yale University School of Medicine and the Howard Hughes Medical Institute, said in an interview. In addition, neutralizing antibodies are only 1 component of the immune system. While antibodies are relatively easy to assess, the assays aren’t yet standardized, and scientists haven’t yet determined how low titers can go and still be protective-known as a correlate of immunity. One of the main arguments for COVID-19 vaccine boosters has been the observation that anti–SARS-CoV-2 antibodies wane over time, which has been seen with other vaccines. However, experience with other vaccines and recent studies examining the durability of the immune response to COVID-19 vaccines so far provide clues. Given that the earliest clinical trial participants received COVID-19 vaccines only about a year and a half ago, predicting how long the immunity they elicit will last is difficult. “I think there’s a high probability that it could be 3 and done.” It’s unlikely that annual doses will be necessary, however, said Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine and codirector of the Texas Children’s Hospital Center for Vaccine Development. “When we gave those first 2 doses so close together, we basically bought ourselves a 3-dose vaccine.”Īccording to the CDC’s “ General Best Practice Guidance for Immunization,” “As a general rule, decreasing the interval between doses in a multiple-dose vaccine series may interfere with antibody response and protection.” Hotez noted that the immune response soars higher and more quickly after a third mRNA vaccine dose administered 8 months after the second dose than it does after the first 2 doses administered only a few weeks apart. The issue with that is when you space them so close together, you don’t get long-lasting protection,” Peter Hotez, MD, PhD, explained in an interview. We did that because we were in dire straits. “When we rolled the 2 mRNA vaccines out, we spaced them pretty close together. The third dose represents completion of the primary vaccine regimen, not a booster, the thinking goes. The billions needed to pay for booster shots for all US adults, as pledged by the Biden administration in August, might provide a bigger bang for the buck if spent on other policies, such as improving vaccine uptake among the 1 in 5 American adults who haven’t received a single dose or reselling or donating doses to countries that don’t have enough first or second doses to go around, authors from Harvard Medical School noted in a recent opinion piece.īut some scientists argue that the first 2 doses of the mRNA COVID-19 vaccines can’t be expected to provide long-lasting immunity because they were administered only 3 or 4 weeks apart. With SARS-CoV-2 “galloping freely” in lower-income countries where few people have been vaccinated, she said, “this is scientifically irresponsible and morally unacceptable.” Some scientists believe that the evidence shows people are fully vaccinated after just 2 doses and that the so-called boosters now recommended for many people in the US, the United Kingdom, Italy, France, Germany, and Ireland accomplish little more than “polishing the immune response of the lucky ones,” as Giovanna Borsellino, MD, PhD, professor of immunohematology at Rome’s Santa Lucia Foundation, put it in an email.
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