Updated Covid-19 boosters that contain instructions to arm the body against currently circulating Omicron subvariants offer some protection against infection, according to the first study to examine booster performance in the real world. However, the protection is not as high as that provided by the original vaccine against earlier variants of the coronavirus, the researchers say.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, called the new data “really, really good.”
“Please, for your own safety, for that of your family, get your updated Covid-19 vaccine as soon as you are eligible to protect yourself, your family and your community,” Fauci said during a briefing at the White House on Tuesday.
The uptake of the bivalent boosters, which protect against the BA.4/5 subvariants as well as against the original viral strain, was remarkably slow. Only 11% of eligible Americans have gotten them since they became available in early September.
The new study revealed that the updated boosters work much like the original boosters. They protect against symptomatic infections in a range of 40% to 60%, which means that even when vaccine protection is strongest, about a month after receiving the vaccine, people may still be vulnerable to breakthrough infections. .
This is roughly in the same range as the typical effectiveness of flu shots. Over the past 10 years, CDC data shows that the effectiveness of seasonal flu vaccines has ranged from a low of 19% to a high of about 52% against the need to see a doctor because of the flu. Effectiveness varies depending on how similar the strains in the vaccine are to the strains that end up making people sick.
The authors of the new study say people should realize that Covid-19 vaccines no longer protect more than 90% against symptomatic infections, as they did when they were introduced in 2020.
“Unfortunately, 90% to 100% protection was what we saw in the pre-Delta period. And so with Delta we saw it drop into the 70% range, and then for Omicron we saw it drop even lower, into the 50% range. And so I think what we’re seeing here is that the bivalent vaccine really brings you back to that kind of efficacy that we would have seen immediately after past boosters, which is great. This is where we want it to happen,” said Dr Ruth Link-Gelles, an epidemiologist at the US Centers for Disease Control and Prevention.
“It’s not 100% protection, but it’s something,” Link-Gelles said. “Especially for holidays where you are likely to travel, to spend time with elderly parents, with vulnerable people. I think it is better to have some protection against infection and therefore some protection against infection of your loved one than to have no protection at all.
Link-Gelles says it also means people should continue to take a layered approach to protection, using rapid testing, good quality masks and ventilation as an overall approach, rather than relying solely on vaccines.
“It should kind of be one of the things in your toolbox to protect yourself and your family,” she said. “Personally we are my family all up to date vaccinated but I think if we go to the airport tomorrow we will wear our N95s [masks] because we are seeing elderly parents this weekend. And while we of course trust vaccines, and I’m not terribly worried about a mild infection in me or my healthy husband, we certainly wouldn’t want to infect his grandmother.
Link-Gelles added that she expects vaccine protection against serious consequences of Covid-19, such as hospitalization and death, to be higher, but that data is not yet available.
The study, which was led by CDC scientists, relied on health records from more than 360,000 tests performed at nearly 10,000 retail pharmacies between September 14 and November 11, a period when the BA.4 and BA.5 subvariants caused most of the Covid. -19 infections in the United States. The study included people aged 18 and over who had symptoms of Covid-19 and were not immunocompromised.
The study looked at the effectiveness of boosters in two ways: researchers calculated a value called absolute vaccine effectiveness, which compared the risks of symptomatic infection in people who received bivalent boosters with those who reported not having been vaccinated. They also calculated the relative efficacy of the vaccine, which looked at the risks of symptomatic infection in people who received updated bivalent boosters compared to those who received two, three or four doses of the original strain vaccine. unique.
Compared to unvaccinated people, adults aged 18 to 49 who received bivalent boosters were 43% less likely to fall ill with Covid-19 infection. Older people, who tend to have lower immune function, have less protection. People aged 50 to 64 were 28% less likely, and those aged 65 and over were 22% less likely to fall ill with Covid-19 than the unvaccinated group.
The relative effectiveness of the vaccine showed the extra protection people could expect on top of the protection they had left after previous vaccine doses. If a person was two to three months after their last vaccine dose, bivalent boosters added an average of 30% protection for people aged 18 to 49, an additional 31% protection if they were 50 to 64 and 28 % additional protection if they were 65 or older. At 3 months after their last booster, people aged 50 and older still had about 20% protection against Covid-19 disease, according to CDC data. So overall, the updated boosters allowed them to achieve about 50% effectiveness against symptomatic infections.
If a person was more than eight months away from their last vaccine dose, they were better protected by boosters. But Link-Gelles said at eight months there was little protection left from previous injections against Omicron and its variants, meaning the vaccine’s effectiveness for this group was likely close to their overall protection against infection. .
People aged 18 to 49 who were eight months or more past their last vaccine dose had 56% more protection against a Covid-19 infection with symptoms; adults aged 50 to 64 had 48% more protection and adults over 65 had 43% more protection, on top of whatever was left over from previous vaccinations.
John Moore, an immunologist and microbiologist at Weill Cornell Medicine, said it boils down to the fact that boosters will likely reduce your risk of getting sick by about 50% and that protection is unlikely to last.
“Having a booster will give you extra protection against infection in the short term, which is always what we see with a booster, but it won’t last long. It will decline, and it will decline further as more resistant variants spread,” said Moore, who was not involved in the new research.
The immunity landscape in the United States is more complex than ever. According to CDC data, about two-thirds of Americans have completed at least their first round of Covid-19 vaccines. And blood test data shows nearly all Americans have some immunity to the virus, through infection, vaccination, or both.
A new pre-publication study Harvard and Yale researchers estimate that 94% of Americans have been infected with the virus that causes Covid-19 at least once, and 97% have been infected or vaccinated, increasing protection against new Omicron infection by about 22 % in December 2021 to 63% by November 10, 2022. Protection of the population against serious diseases has increased from around 61% in December 2021 to around 89%, on average, in November.
All of this means that the United States is in a better position, at least defensively, than it has ever been against the virus – which is not to say that the country could not see another wave of Covid-19, especially if a new variant emerges that is very different from what we have seen, if immunity continues to decline, or if behavior changes drastically.