Editor’s note: Find the latest COVID-19 news and guidance in Medscape’s Coronavirus Resource Center.
Two new studies further demonstrate the ability of the Omicron variant to avoid vaccine- or infection-induced immunity.
The surveys, published January 20 in the journal Natural Medicine, also reinforce the importance of boosters worldwide.
In a study, Samuel MS Cheng, from the School of Public Health, University of Hong Kong, and colleagues compared differences in antibody response to infection with the wild-type or Omicron variant of SARS-CoV-2 in several groups that had either recovered . from COVID-19 (30 persons) or received vaccinations.
The groups that received vaccinations included: uninfected humans 1 month after their second dose of either the Pfizer-BioNTech vaccine (31 participants) or the CoronaVac vaccine (developed by the Chinese company Sinovac Biotech) (30 people); those who received two doses of CoronaVac and an additional booster of CoronaVac (30 participants); or three doses of Pfizer-BioNTech (25).
The researchers found that a Pfizer booster after two initial doses of the mRNA vaccine or the CoronaVac-inactivated virus vaccine provided acceptable immunity to Omicron 1 month after booster dose administration.
Acceptable was defined as “antibody levels sufficient to induce more than 50% protection against SARS-CoV-2.”
However, the study shows that only two original doses of the Pfizer or CoronaVac vaccines provided low protection against Omicron even 3-5 weeks after vaccination.
The authors found that a CoronaVac booster after two original shots of CoronaVac did not develop neutralizing antibodies to Omicron in most recipients.
“Our results suggest that countries that primarily use CoronaVac vaccines may need to consider mRNA vaccine boosters in response to the spread of Omicron,” the authors write.
The researchers note that more than 750 million doses of CoronaVac have been given in more than 40 countries.
Comparison of protection against variants
In the second study, lead author Eddy Pérez-Then, MD, MPH, with the Department of Health in Santo Domingo, Dominican Republic, and colleagues examine the effectiveness of a three-part vaccine, consisting of two doses of CoronaVac, followed by at least 4 weeks later by a Pfizer- booster against the Delta and Omicron variants (in 101 participants) in the Dominican Republic.
The three-part vaccine induced elevated levels of virus-specific antibodies and strong antibody neutralization against both the original form of SARS-CoV-2 and the Delta variant compared to pre-mRNA booster levels.
Researchers found that neutralization of Omicron was undetectable in those who had received only two doses of CoronaVac. However, the addition of an additional Pfizer booster vaccination to this regimen resulted in a 1.4-fold increase in antibody neutralization against Omicron compared to those who received two doses of either the Pfizer-BioNTech or Moderna vaccines.
Carolina Lucas, PhD, postdoc at the Department of Immunobiology, Yale University School of Medicine in New Haven, Connecticut, told Medscape Medical News the data suggest that the Pfizer booster is extremely effective for people who received the CoronaVac regimen.
“But,” she said, “it is still important to note that the neutralization titers against Omicron were significantly reduced compared to [neutralizing antibody] levels of ancestral virus and Delta variant post booster (7.1-fold and 3.6-fold, respectively), suggesting a greater risk of vaccine breakthrough infections. “
By comparing the two studies in Natural medicine, Lucas said, both studies highlight data about CoronaVac, which is important as it is the world’s most widely used vaccine.
The methodology for both studies is very similar, she noted, “and we both demonstrated the benefits of the booster shot using. [Pfizer’s] BNT162b2 mRNA vaccine, highlighting the global need for vaccine boosters to combat the effects of new variants. “
“The biggest discrepancy is among the analysis of neutralizing antibodies [after] 2 doses of Pfizer, “said Lucas.” Their results are lower compared to ours [studies] and other studies, but the analysis [after] the heterologous booster regimen is consistent. “
The authors state in a press release: “It is noteworthy that previous infection with SARS-CoV-2 did not significantly increase the level of antibodies to Omicron in participants who had received the mixed vaccine regimen.”
Sara Cherry, PhD, professor of pathology and laboratory medicine at the University of Pennsylvania in Philadelphia, told Medscape Medical News“” These articles suggest that a coherence of protection, neutralizing antibodies, is low compared to the standard vaccination schedules, but that a booster can increase the levels of neutralizing antibodies against Omicron significantly. This is good news for those who have access to boosters. “
She said it was important to remember that globally there is clear evidence that vaccination protects against hospitalization and death, even with low neutralization titers.
This suggests that neutralization is one of many facets of immune protection [that] vaccination provides, she said.
The good news is that current vaccines provide protection against the worst results, and the even better news is that a boost will improve our immunity to Omicron.
“The good news is that current vaccines provide protection against the worst results, and the even better news is that a boost will improve our immunity to Omicron,” Cherry said.
Both articles were published online in an accelerated preview. Financial information and financing are available with the full text of both papers. Cherry has not disclosed any relevant financial matters.
Natural medicine. Cheng et al. Published online January 20, 2022. Full text
Natural medicine. Pérez-Then et al. Published online January 20, 2022.
Marcia Frellick is a Chicago-based freelance journalist. She has previously written for the Chicago Tribune, Science News and Nurse.com and was editor of the Chicago Sun-Times, Cincinnati Enquirer and St. Cloud (Minnesota) Times. Follow her on Twitter at @mfrelick
Discussion about this post