According to Hong Kong’s “South China Morning Post” website reported on May 16, as new crown cases surged again, many countries began to promote the fourth dose of the new crown vaccine, which is the second booster dose.
However, the vast majority of second-dose booster vaccination programs target only the elderly and immunocompromised populations. That’s because scientists aren’t sure how long the immunity from the second booster will last, or whether the second booster will benefit the general population.
Scientists have done some research around the effectiveness of the second booster shot, but more needs to be done. The research data to date tells us the following facts:
How effective is the second booster dose in older adults?
Most of the research data to date have come from Israel, as Israel was the first to begin testing populations 60 and older and high-risk groups such as immunocompromised and their caregivers) to receive the second booster dose.
One study compared the effectiveness of the first booster dose with the second booster dose using Pfizer’s messenger ribonucleic acid (mRNA) vaccine. The researchers looked at the health records of more than 182,000 people aged 60 and older during the Omicron variant-dominated outbreak from Jan. 3 to Feb. 18 of this year.
The results of the study were published last month in the New England Journal of Medicine. The researchers found that a second booster dose significantly reduced the risk of severe illness, hospitalization and tragic death in older adults for at least a month.
Compared with people who received only one booster dose, subjects were more effective at preventing infection within 7 to 30 days after receiving the second booster dose. The relative effectiveness in preventing symptomatic infection was 55%, the relative effectiveness in preventing hospitalization was 68%, the relative effectiveness in preventing severe illness was 62%, and the relative effectiveness in preventing death was 74%.
Another study, published earlier in the New England Journal of Medicine, looked at breakthrough infections (remaining infected with the virus after vaccination—in people 60 and older— Note in this newspaper) and the incidence of severe disease. The study involved more than 1.2 million elderly people in Israel. The researchers found that during the epidemic of the Omicron variant, people who received only one booster dose had a 3.5 times higher risk of developing severe cases than those who received a second booster dose.
The researchers also found that the number of infections per 100,000 people was 177 for older adults who received a second booster dose. In comparison, among older adults who received just one booster dose, 361 cases per 100,000 people were diagnosed.
Is the second booster safe?
A second-dose booster trial conducted by British scientists has found some cases of serious adverse reactions, but the researchers believe these cases are not related to the vaccine itself. The most common side effect is pain at the injection site, which is mostly mild or mild. Fatigue, headache, malaise, and muscle pain are also more common.
How long does the protection last?
The above-mentioned study involving more than 1.2 million elderly Israelis showed that the second dose of boosted protection against severe disease did not provide protection for the 6 weeks after the subjects were vaccinated. A drop occurs.
The researchers also found that the ability of the second booster dose to prevent infection decreased four weeks after vaccination, and they believe more follow-up studies are warranted.
The British trial found that if a second booster dose of mRNA vaccine was administered more than 6 months after the first booster dose was administered, the anti-spike protein in the subjects was significantly reduced. Antibody titers will rise substantially. But the researchers also said that this value is likely to “fall back quickly” because of similar situations after the first booster dose.
Will everyone benefit?
From the limited trial data to date, although the second booster dose is thought to be beneficial for the at-risk population, its implications have broader implications. It’s probably not that noticeable in the crowd.
In a non-randomized, open-label clinical study in Israel, 272 healthcare workers received a second dose of a Pfizer or Moderna mRNA booster. Health care workers of a similar age structure who did not receive the second booster dose constituted the control group, twice as many as the experimental group.
The researchers found that the antibodies produced by the second booster shot can neutralize the mutant strains such as Omicron, while the effect of the Pfizer vaccine and the Moderna vaccine was not obvious. difference.
However, compared with the first booster, the second booster showed no substantial difference in humoral immune responses and levels of Omicron-specific antibodies . The team believes that this shows that the three-shot vaccine has stimulated the immune response to the greatest extent.
“A fourth dose of the vaccine for healthy young health care workers may provide only a small benefit,” the researchers wrote.
(Source: Reference News)