Amid the increasing cases of new coronavirus variants all across the world, several questions are being raised about how well are the ones protected who’ve already had their COVID-19 shots are against evolving forms of the SARS-CoV-2 virus.
Hence here, microbiology and infectious disease specialist William Petri of the University of Virginia answers some common questions about COVID-19 booster shots.
- What is a booster shot?
William Petri said, Boosters are just an extra dose of a vaccine that are given to maintain vaccine-induced protection against a disease. These are the shots that are commonly used to boost several vaccines because the immunity can decrease over time. Like for instance, the flu vaccine needs a booster every year, and the diphtheria and tetanus vaccine every 10 years.
Booster shots are often identical to the original vaccine. However, in some cases, the booster shot has been modified to increase protection against new viral variants. For the seasonal flu vaccine, the booster is generally needed as the flu virus changes frequently
The seasonal flu vaccine, most notably, requires an annual booster because the flu virus changes so quickly.
- Do I need to get a COVID-19 booster?
Only if you’re immunocompromised says Petri. As of August 2021, it was recommended by the U.S Food and Drug Administration and Centers for Disease Control and Prevention, for adding third shot to the normal vaccination course for people who are severely immunocompromised.
- Why aren’t booster shots recommended for everyone yet?
It is not clear yet when a booster will be required, while vaccine-induced immunity may not last forever. Hence, encouragingly, all of the currently authorized coronavirus vaccines tempt a robust immune memory against the COVID-19. Your immune system’s memory B cells are taught by the vaccines to produce antibodies when you are exposed to the virus.
Hence, researchers have detected high levels of memory B cells in the lymph nodes of people who received the Pfizer vaccine for at least 12 weeks after they got the shot.
According to studies conducted it has been suggested that authorized coronavirus vaccines are continuing to provide protection even against developing strains of the coronavirus. Among one study’s participants, the Johnson & Johnson vaccine had 73% and 82% efficacy 14 days and 28 days post shot, respectively, at warding off severe disease from the beta variant.
Another study found the Pfizer vaccine to be 88% effective against the delta variant.
The other source of long-lasting antibody responses against the coronavirus is cells called plasmablasts that reside in the bone marrow. These cells continuously produce antibodies and do not require boosting to maintain their activity. Fortunately, plasmablasts have been detected in the bone marrow of people who received the COVID-19 vaccine for up to 11 months, indicating some degree of long-lasting immune memory.
- How will I know if I need a booster?
You may need to wait for an outbreak in people who have been vaccinated. Researchers are still figuring out the best way to measure the strength of someone’s vaccine-induced immunity. The COVID-19 vaccines have been so effective that there are not many failures to test.
The best candidate to measure are certain antibodies the vaccine induces the immune system to make. They recognize the spike protein that allows the coronavirus to enter and infect cells. Evidence supporting the importance of anti-spike antibodies includes a study showing that the somewhat more effective mRNA vaccines like Pfizer and Moderna generate higher antibody levels in the blood than the adenovirus vector vaccines like Johnson & Johnson and AstraZeneca.
In a preliminary study that has not yet been peer-reviewed, anti-spike antibody levels were lower in people who caught COVID-19 after they were vaccinated with the Oxford-AstraZeneca vaccine.
Medical workers would love to be able to give patients a blood test that would tell them how well protected they are or aren’t against COVID-19. That would be a clear indication as to whether a booster shot is needed.
But until researchers know for sure how to measure vaccine-induced immunity, the next indication that boosters may be needed are breakthrough infections in older adults who have already been vaccinated. People over the age of 80 make lower levels of antibodies after vaccination, so their immunity may wane sooner than that of the general population. The elderly would also most likely be the most susceptible to new viral variants that evade the protection current vaccines provide.
- Who does the FDA and CDC recommend get a third shot?
An extra shot may be necessary for certain immunocompromised people. In one study, 39 of 40 kidney transplant recipients and a third of dialysis patients failed to make antibodies after vaccination. Another study identified 20 patients with rheumatic or musculoskeletal diseases on medications that suppress the immune system who also did not have detectable antibodies. Both of these studies were done after patients received the full vaccine dose.
Currently, the CDC recommends that the following people consider getting a third dose:
- People in active cancer treatment
- People who have received organ transplants and are taking immunosuppressive therapy
- People who have received a stem cell transplant within the past two years or are taking immunosuppressive therapy
- People with moderate or severe primary immunodeficiency
- People with advanced or untreated HIV infection
- People taking high-dose corticosteroids and other immunosuppressive drugs
- Does my third dose need to match my first two?
Likely not. Recent research has shown that mRNA vaccines, like Pfizer and Moderna, can be mixed with adenovirus-based vaccines like AstraZeneca with comparable results.
