Should we take the fourth dose of COVID-19 vaccine? The research data so far tells you these facts

According to the Hong Kong "South China Morning Post" website on May 16, as the number of new coronavirus cases surged again, many countries began to promote the fourth dose of the new coronavirus vaccine, which is the second booster shot.

However, most second-dose booster vaccination programs are only for the elderly and people with immune deficiencies because scientists are not sure how long immunity from the second booster lasts or whether it will benefit the general population.

Scientists have conducted some research on the effectiveness of a second booster shot, but more research is needed. Here’s what the data so far tells us:

How effective is the second booster dose for older adults?

Most of the research data so far come from Israel, as it was the first country to begin giving second booster doses to people aged 60 and older and to high-risk groups, such as the immunocompromised and their caregivers.

One study used Pfizer's messenger RNA (mRNA) vaccine to compare the effectiveness of the first booster shot with the second booster shot. The researchers investigated the health records of more than 182,000 people aged 60 and above from January 3 to February 18 this year, when the Omicron variant dominated the epidemic.

The New England Journal of Medicine published the results of the study last month. Researchers found that the second booster shot can significantly reduce the risk of severe illness, hospitalization and death in the elderly for at least one month.

Compared with people who only received one booster shot, the relative effectiveness of preventing infection reached 45% within 7 to 30 days after receiving the second booster shot, the relative effectiveness of preventing symptomatic infection was 55%, the relative effectiveness of preventing hospitalization was 68%, the relative effectiveness of preventing severe illness was 62%, and the relative effectiveness of preventing death was 74%.

Another study published earlier in the New England Journal of Medicine examined the incidence of breakthrough infections (referring to infection with the virus after vaccination - note from this newspaper) and severe illness in people aged 60 and above. 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 shot had a 3.5 times higher risk of developing severe cases than those who received the second booster shot.

The researchers also found that for older people who received a second booster shot, the infection rate was 177 per 100,000 people, compared with 361 per 100,000 people who received only one booster shot.

Is the second booster shot safe?

The second booster shot trial conducted by British scientists found some serious adverse reactions, but researchers believe that these cases are not related to the vaccine itself. The most common side effect is pain at the injection site, and the symptoms are mostly mild or mild. Fatigue, headache, malaise and muscle pain are also common.

How long does the protection last?

The above study involving more than 1.2 million elderly Israelis showed that the second dose of enhanced protection against severe illness did not decrease in the six weeks after the subjects were vaccinated.

The researchers also found that the ability of a second booster shot to prevent infection declined four weeks after vaccination, and they believe more follow-up studies are needed.

The British trial found that if the second dose of the mRNA vaccine booster was given more than 6 months after the first dose, the titer of anti-spike protein antibodies in the subjects would increase significantly. However, the researchers also said that this value is likely to "fall back quickly" because similar situations have occurred after the first dose of the booster.

Can it benefit everyone?

Based on the limited trial data currently available, although the second booster dose is considered to be beneficial for at-risk groups, its significance may not be as significant for the wider population.

In a non-randomized, open-label clinical study in Israel, 272 medical staff received a second dose of Pfizer or Moderna's mRNA booster shot. The control group consisted of medical staff of similar age who did not receive the second booster shot, with twice the number of people in the experimental group.

Researchers found that the antibodies produced by the second booster shot were able to neutralize variants such as Omicron, and there was no significant difference in the effectiveness of the Pfizer and Moderna vaccines.

However, compared with the first booster shot, the second booster shot showed no substantial difference in humoral immune response and Omicron-specific antibody levels. The research team believes that this shows that the three-shot vaccine has stimulated the immune response to the greatest extent.

"Giving a fourth dose to healthy, younger health care workers may provide only a small benefit," the researchers wrote.

(Source: Reference News)