Why the third dose of COVID-19 vaccine is critical against Omicron

Why the Third Booster Dose of COVID-19 Vaccine is Critical Against Omicron

The immunity of coronavirus vaccines disappears over time, but the data shows that boosters offer better protection against all variants, including the newest strain, Omicron.

As the number of positives of the new Omicron variant spreads, experts say the best defense against all viral variants that cause COVID-19 is a full dose of the vaccine followed by a booster vaccine about six months after the initial regimen has ended. In Spain, last week the Ministry of Health authorized the booster dose for people over 40 years of age. The third dose seems to have ceased to be an option to become the best source of guarantees against the coronavirus.

Since the first COVID-19 mRNA vaccine was authorized on December 11, 2020, studies have shown that unvaccinated people have a five-fold higher risk of becoming infected and a 10-fold higher risk of hospitalization or death from COVID-19 than those who are fully vaccinated.

Research conducted in Israel and the United States has also revealed that immunity induced by the SARS-CoV-2 coronavirus vaccine decreases after six to eight months. This is especially concerning as more populations are exposed to the more contagious Omicron variant, which was first detected in November in South Africa.

In the graph we can see how the effectiveness of COVID-19 vaccines in the two strains evolves over the weeks. Although vaccines are less effective with Ómicron than with Delta, boosters restore effectiveness almost completely.
In the graph, we can see how the effectiveness of COVID-19 vaccines in the two strains evolves over the weeks. Although vaccines are less effective with Ómicron than with Delta, boosters restore effectiveness almost completely.

To date, Omicron has been reported in 77 countries. In the United States, the variant is found in more than 37 states and constitutes 3% of total cases; the rest are still Delta. The United Kingdom currently concentrates the highest number of infections by the new SARS-CoV-2 strain positively diagnosed, while in South Africa it is the dominant variant.

Boosters, however, can restore antibody levels to their maximum values, providing stronger protection against Omicron.

“Vaccines help 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 whatever it is, Omicron or Delta, having a booster will be beneficial.”

What are booster doses?

COVID-19 vaccines train our immune system to produce antibodies using synthetic versions of the virus’ spike protein, the part of the virus that helps it bind to human cells. If a vaccinated person subsequently encounters the virus, the antibodies recognize it and bind to the spike protein to prevent infection.

The first dose of an mRNA vaccine prepares cells to produce antibodies, and the second dose matures and enhances those antibodies so that they bind even more strongly to the spike protein so that it cannot be anchored to receptors on human cells. In the case of the Johnson & Johnson or Janssen vaccine, a single dose was enough to produce enough antibodies against the original coronavirus.

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

The U.S. Centers for Disease Control and Prevention (CDC) currently recommends the booster dose for everyone 18 and older. The CDC says people should receive a booster dose six months after the second dose of the Pfizer or Moderna mRNA vaccines, or two months after the Janssen vaccine. The CDC has also recommended boosters for 16- and 17-year-olds who have been fully vaccinated with two doses of the Pfizer vaccine.

Scientists are still gathering evidence to find out how long booster immunity lasts and whether more will be needed in the future.

How does Omicron affect vaccines?

Since Omicron has accumulated more than 30 mutations in the spike protein alone compared to the original virus, it appears to evade antibodies generated by two doses of the Pfizer or Moderna vaccines, or the single dose of the Janssen vaccine, especially when antibody levels drop in the blood.

In a study conducted in the UK that has not yet been peer-reviewed, the efficacy of two injections of the Pfizer or AstraZeneca (Covishield in India) vaccines in preventing Omicron’s COVID-19 symptoms fell to less than 40% in the 15 weeks following the second dose. The efficacy of Pfizer’s vaccine against Delta decreased less, but the efficacy of the vaccine continued to fall to 60% after 25 weeks.

Other preliminary studies conducted in South Africa, Israel, and France also show a sharp decline in the ability of antibodies to neutralize Omicron in people vaccinated with Pfizer’s two-dose vaccine or two doses of Moderna’s vaccine.

Reinforcements continue to work against Ómicron

The good news is that a booster dose of Pfizer’s vaccine increases antibody levels up to 25 times, which should be enough to neutralize the Omicron variant. A booster dose of Moderna’s vaccine has also been shown to improve Omicron neutralization compared to the previous two injections alone.

“The two doses with declining immunity mean a disappearance of protection after a few months,” says Peter Hotez, a pediatrician and vaccine scientist at Baylor College of Medicine in Texas. “Reinforcement at least gives you something in the 70% range.”

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

“Our booster vaccine regimens work against Omicron,” Anthony Fauci, Chief Medical Advisor to the President of the United States and the face of the fight against COVID in the country, said during a COVID-19 update at the White House on Dec. 15. “At this time, there is no need for a specific reinforcement for the variant,” Fauci added.

However, the data obtained so far come largely from laboratory studies, and immunity involves more than just antibodies. More real-world data will be important to assess the long-term efficacy of current Omicron vaccines.

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