Second COVID booster shot does little to stop Omicron, study finds

Israeli healthcare workers who were boosted with a fourth dose of COVID-19 at the height of the Omicron wave were only marginally better protected from re-infection than their counterparts who received three shots, researchers reported Wednesday.

Compared to two starting doses and one booster dose of Pfizer and BioNTech’s Comirnaty vaccine, the addition of a second booster dose reduced the rate of coronavirus infection by just 30%.

The fourth dose was slightly more effective at preventing COVID-19 symptoms, according to a study published in the New England Journal of Medicine. Health care workers who received the second booster shot were 43% less likely to show signs of illness than those who had not.

Using Spikevax, Moderna’s COVID-19 vaccine, as a second booster shot was even less effective at preventing coronavirus infection in this group of younger, generally healthy Israelis. Recipients were only 11% less likely to be reinfected during the Israeli Omicron wave than those who received three vaccine doses and were 31% less likely to experience symptoms of COVID-19.

The benefits of a second booster shot were initially small. But they were even smaller considering how effective three doses of vaccine had reduced the effects of a coronavirus infection to a mere nuisance.

Regardless of whether they received three or four doses of COVID-19 vaccine, most Israeli doctors and nurses who participated in the new study and then became infected “reported negligible symptoms,” the study authors noted. This means that the practical benefit of a fourth dose would hardly have been felt in the study population of 821 people.

The researchers also observed that those who received a fourth dose and subsequently became infected had “relatively high viral loads.” This suggests that the added booster did little to curb their ability to spread the virus to others.

“A fourth vaccination of healthy young health workers may only have marginal benefits,” the Israeli researchers concluded. The extra injection reliably boosted the coronavirus antibodies, but the protective value of the mRNA vaccines appears to have been matched by three doses, they added.

The newly released study comes a day after Pfizer asked the Food and Drug Administration to approve a second booster shot for Americans age 65 and older.

Pfizer cited the results of two unpublished Israeli studies.

In a press release announcing its application to the FDA, Pfizer said an analysis of Israeli medical records showed that the rate of confirmed infections in people aged 60 and older who received a second booster shot was half that of their peers, who had only received three doses of the vaccine. In addition, the group who received a second booster shot were four times less likely to develop severe COVID-19, the company said.

Pfizer’s FDA filing also included results from an unspecified clinical trial in which it offered a second booster shot to Israeli healthcare workers who requested it. Among the 154 workers who received the fourth injection, neutralizing antibodies increased by a factor of seven to eight and antibodies specific to the Omicron variant increased by a factor of eight to ten, Pfizer said.

While the study design and the names of the researchers conducting the study are unclear in Pfizer’s press release, these results appear to reflect a segment of the population that was the subject of Wednesday’s New England Journal of Medicine study.

While vaccine experts await a more complete account of the data Pfizer cited, they pointed to the newly published Israeli study as proof that any discussion of the second booster is premature for everyone.

The FDA and the Centers for Disease Control and Prevention have already approved and recommended a fourth dose of the mRNA vaccine for Americans ages 12 and older with moderately to severely compromised immune systems from disease or medications.

The CDC has also recommended a booster dose of Comirnaty for people 12 years and older who received their second dose of vaccine at least 5 months prior. But dr Paul Offit, an infectious disease expert at the Children’s Hospital of Philadelphia, said that for older and sicker Americans, three shots should probably be considered the first series. The case for a possible fourth shot — a booster — for these Americans has yet to be made, he added.

For most people, two to three doses or mRNA vaccine virtually eliminated the risk of infection progressing to serious illness or death, Offit said. It is difficult to prove that the immune system needs more vaccines to protect against the SARS-CoV-2 virus, he added.

“If we are to overcome this pandemic, we must recognize that protection from mild illnesses will not last long,” Offit said. The key is recognizing that infections that are little more than a cold and cough do not warrant efforts to prevent them. “As long as protection against serious diseases lasts, we should consider this a victory,” he said.

dr William Schaffner, an infectious disease physician at Vanderbilt University, agreed that three doses of the vaccine continue to provide very good protection against serious illness for most people.

“So far we’re in good, solid shape,” said Schaffner, who hailed the new Israeli study as further evidence of that.

Schaffner added that there is growing frustration among scientists and researchers over the release of data by vaccine manufacturers that have not passed the scientific review required for publication in a scientific or medical journal. He called Pfizer’s scientific claims “inappropriate” in the press release.

“It’s wonderful that Pfizer has put this vaccine on the shelf for us to pull down if needed,” he said. “But the ‘if’ and the ‘when’ are the responsibility of the FDA and the CDC. Getting it on the shelf is Pfizer’s job. We would prefer them to stick to knitting.” Second COVID booster shot does little to stop Omicron, study finds

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