How booster shots can help protect you from Omicron

Immunity from COVID-19 vaccines fades over time, but data show boosters do offer better protection against all variants—including the more contagious Omicron.

Published 20 Dec 2021, 09:52 GMT
A health worker prepares a Pfizer-BioNTech shot at the Civil hospital in Nepal. The Pfizer vaccine ...
A health worker prepares a Pfizer-BioNTech shot at the Civil hospital in Nepal. The Pfizer vaccine was provided by the U.S government through COVAX facility.
Photograph by Dipendra Rokka/SOPA Images/LightRocket via Getty Images

As the new Omicron variant spreads, experts say the best defence against all viral variants that cause COVID-19 is a full dose of a vaccine followed by a booster shot several months later.

Since the first vaccines against COVID-19 were deployed on December 8, 2020, studies have shown that unvaccinated people are at five times greater risk of getting infected and 10 times greater risk of hospitalisation or death from COVID-19 than those who are fully vaccinated.

But research from Israel and the U.S. also revealed that vaccine-induced immunity against the SARS-CoV-2 coronavirus wanes in six to eight months. That’s especially worrying as more populations are exposed to the more contagious Omicron variant, which was first detected in November in South Africa.

To date Omicron has been reported in 77 countries. In England and Scotland it now makes up the majority of positively diagnosed SARS-CoV-2 infections, and in South Africa it is the dominant strain.

Boosters, however, can restore antibody levels to their peak values—providing more robust protection against Omicron.

“Vaccines help to protect you, or at least prevent you from dying from the disease,” says Leo Poon, a virologist at the University of Hong Kong who detected some of the first cases of Omicron outside of South Africa. “And no matter what it is, Omicron or Delta, having a booster will be beneficial.”

What is a booster?

COVID-19 vaccines train our immune systems to make antibodies using synthetic versions of the virus’s spike protein—the part of the virus that helps it bind to human cells. If a vaccinated person later encounters the virus, the antibodies recognise it and bind to the spike protein to prevent infection.

The first dose of an mRNA vaccine prepares the cells to make antibodies, and the second dose matures and enhances those antibodies to bind even more strongly to the spike protein, so that it can’t anchor to receptors on human cells. In the case of the Johnson & Johnson vaccine, a single dose was enough to make sufficient antibodies against the original coronavirus.

But for all COVID-19 vaccines authorised to date, antibody levels do gradually decline, says Maria Elena Bottazzi, a vaccinologist at Texas Children’s Centre for Vaccine Development at Baylor College of Medicine. That’s where boosters come in.

In the U.K. and U.S., the booster dose is currently recommended by the N.H.S. and the U.S. Centres for Disease Control and Prevention for everyone eligible ages 18 and older. Scientists are still gathering evidence for how long immunity from the booster lasts and whether more will be needed down the line.

How does Omicron affect vaccines? 

Since Omicron has accumulated over 30 mutations in the spike protein alone compared to the original virus, it seems to evade antibodies generated by two doses of the AstraZeneca, Pfizer or Moderna vaccines, especially as antibody levels drop in the blood.

In a U.K. study that’s not yet been peer reviewed, the effectiveness of two shots of the Pfizer or AstraZeneca vaccines in preventing COVID-19 symptoms from Omicron fell to less than 40 percent within 15 weeks after the second dose. There was a lesser decline in the effectiveness of the Pfizer vaccine against Delta, but vaccine effectiveness still slipped to just 60 percent after 25 weeks.

Other preliminary studies from South Africa, Israel, and France also show steep declines in the ability of antibodies to neutralise Omicron in people vaccinated with the two-dose Pfizer vaccine or two doses of Moderna’s vaccine.

Boosters still work against Omicron

The good news is that a booster dose of the Pfizer vaccine increases antibody levels by 25-fold, which should be sufficient to neutralise Omicron. A booster dose of Moderna’s vaccine also improved the neutralisation of Omicron compared to the previous two shots alone.

“The two doses with waning immunity mean there's no protection within a few months after the two doses,” says Peter Hotez, a paediatrician and vaccine scientist at Baylor College of Medicine. “The booster at least gives you something in the 70 percent range.”

Other studies show that when people received any mRNA booster dose, their antibody levels against Omicron rose to the protective level considered sufficient to prevent a COVID-19 infection.

“Our booster vaccine regimens work against Omicron,” U.S. Chief Medical Advisor Anthony Fauci said during a White House COVID-19 update on 15 December. “At this point, there is no need for a variant-specific booster,” Fauci added.

However, the data so far is largely from laboratory studies, and immunity involves more than just antibodies. More real-world data will be important to assess how effective current vaccines will be against Omicron in the long run.

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