Home / Science / Health /  ‘2 vaccine doses give no protection against Omicron but…’ Experts on how to prevent infection
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Antibodies produced by the first two doses of mRNA vaccines wanes over time and practically provide zero protection against Omicron, a new study has revealed. It further suggested that breakthrough infections after 2-vaccine doses also don't make a significant difference in the case of Omicron. The same team of scientists, however, had earlier suggested that mRNA vaccine booster dose produced effective levels of neutralising antibodies against the COVID variant. 

"Our new work shows that two doses of mRNA vaccine do not offer protection against Omicron, and even having a breakthrough infection on top of vaccine does not help much. But our earlier study showed that the booster can really rescue the shortcomings of the two doses," said Shan-Lu Liu, the senior author of both studies and a virology professor at Ohio State University, US.

"Serum samples were collected pre-vaccination, three to four weeks after a first vaccine dose, three to four weeks after a second vaccine dose and six months after the second vaccine," Liu said.

The new study, published in the journal Science Translational Medicine, examined antibodies in serum samples from 48 health care professionals with experimental versions of the parent virus and the Alpha, Beta, Delta and Omicron variants.

Breakthrough infection and Omicron

The authors suggest the neutralising antibodies increase substantially after the second dose against every variant except the Omicron variant. "From the second dose to six months later, there was an at least five-fold drop in immunity, even against the parent virus," John Evans, a Ph.D. student at Ohio State University.

Although the findings suggested a breakthrough COVID-19 infection on top of vaccination increased immunity against most versions of the virus, antibodies from only one individual with previous infection reached levels that could put up a reasonable fight against Omicron."Overall, nobody in this study had good immunity against Omicron," said Liu.

The third dose is critical

Liu noted the dramatic reduction in immunity six months after two vaccine doses and the finding of the earlier study that a booster protects against Omicron highlight how important a third shot is to avoiding infection.

"After the second vaccine dose, the neutralising antibodies effective against Omicron dropped 23-fold, but with a booster shot, immunity dropped only three- to four-fold -- which is comparable to booster effectiveness previously reported against the Delta variant," he added.

The experimental viruses were what are called pseudoviruses -- a non-infectious viral core decorated with different SARS-CoV-2 spike proteins on the surface structured to match known mutations in the variants studied.

Results also showed that people who received the Pfizer mRNA vaccine produced about two-fold lower levels of neutralising antibodies than those who received the Moderna preventive. Men also had significantly higher antibody levels compared to women against all variants over the post-vaccination time points, the researchers said.


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