As new variants of Covid-19 keep emerging, many people are left wondering if they need another vaccine booster. According to several recent studies, two or three vaccines are enough to protect most people from severe illness and death for a long time.
During the pandemic, the focus has been primarily on antibodies, which are the body’s first line of defense because they’re easy to study—all you need is a drop of blood. They rise rapidly after every vaccine shot or each exposure to the virus. However, they naturally decline within a few weeks or months.
As a result of the decrease in antibody levels, the federal government recommended a booster, a third shot, for everyone over 12. One study found that the third shot of either the Pfizer-BioNTech or Moderna vaccines prompted the body to make a much wider variety of antibodies. Recent data from the Centers for Disease Control and Prevention (CDC) discovered that while the extra shot helped raise immunity levels and contained omicron’s spread, the level of antibodies began to decrease after four months.
Antibodies work by recognizing two or three key parts of the spike protein, which is a protrusion on the outside of the coronavirus that allows it to attach to human cells. However, other specialized immune cells, T cells, can detect many more parts of the spike, making them less likely to fail when the virus mutates. Another type of immune cell, B cells, act as memory cells, so when they get triggered, they can create new groups of antibodies within four to five days after another exposure to the virus. The evidence indicates that the B cells appear to learn to recognize a diverse set of viral genetic sequences. The longer they have to practice, the broader the range of virus variants they can combat, which means the immune system’s ability to respond could be very long-lived.
Vaccines from the four brands of Covid vaccine — Pfizer-BioNTech, Moderna, Johnson & Johnson, and Novavax—create T cells and encode memory into B cells. According to the latest research, they’re about 80 percent as effective against omicron as other variants. Since omicron’s mutations are different from previous variants, it’s very likely that the vaccines, especially after a third dose, would provide a vigorous attack on any future variant. One study found that more than half of the antibodies seen one month after a third dose could neutralize omicron, even though the vaccine wasn’t designed for it.
There’s still a lot to learn regarding specialized immune system cells since analyzing them requires milliliters of blood, sophisticated equipment, skill, and time. These factors contribute to why findings are lagging behind those on antibodies. One big unknown is how slowly the T cells may decline and how long-lasting two or three vaccine doses can create.
As of now, experts point out that we’re seeing no additional benefits from receiving more vaccine doses. The only individuals who might benefit from a fourth vaccine are those over 65 or at high risk of illness. As a result, federal health officials have stated that they aren’t planning on recommending fourth doses anytime in the near future.