The B.1.1.529 variant (Omicron), which was initially identified in early November 2021 in South Africa, was labeled a Variant of Concern by WHO on November 26, 2021. According to WHO, the variant was concerning because it contained a significant number of mutations and might evade vaccine-acquired immunity.
A study from Denmark completed in late 2021 noted that fully vaccinated individuals were at greater risk of COVID-19 infection than unvaccinated, and those who received a booster dose were at an even greater risk of infection from the Omicron variant of COVID-19.
In January 2022, a paper completed in Canada studied the data from person 18 years of age and older who had a PCR test for SARS-CoV-2 between November 22 and December 19, 2021. The study, which excluded long-term care residents and individuals who had received only one COVID-19 vaccine dose or who had received their second dose less than 7 days prior to being tested, reported:
“…receipt of 2 doses of COVID-19 vaccines was not protective against Omicron infection at any point in time, and VE was –38% (95%CI, –61%, –18%) 120-179 days and –42% (95%CI, –69%, –19%) 180-239 days after the second dose. VE against Omicron was 37% (95%CI, 19-50%) ≥7 days after receiving an mRNA vaccine for the third dose. Findings were consistent for any combination of 2 mRNA vaccines and 2 doses of BNT162b2 for the primary series.”
The authors concluded that “two doses of COVID-19 vaccines are unlikely to protect against infection by Omicron. A third dose provides some protection in the immediate term, but substantially less than against Delta.”
A CDC study published in February 2022 reported that after four months, a third dose of COVID-19 vaccine was significantly less effective at protecting a person against severe COVID-19 illness caused by the Omicron variant. According to this study, the effectiveness of the third dose against hospitalization dropped from 91 percent at two months to only 78 percent at four months. Effectiveness of the booster dose against urgent care or emergency room visits decreased from 87 percent at two months to 66 percent at four months. By five months, the effectiveness was found to be only 37 percent.
A study published in the New England Journal of Medicine in June 2022 found that two doses of COVID-19 vaccine did not offer any protection against the Omicron variant and could potentially increase a person’s risk of infection.
An article published in the New England Journal of Medicine in September 2022 found that children who had COVID-19 illness and were subsequently vaccinated with the Pfizer-BioNTech mRNA COVID-19 vaccine were more likely to get COVID-19 illness during the Omicron wave. Children who had not experienced a COVID-19 illness but received a COVID-19 vaccine were also more likely to become infected from the Omicron variant. Children with natural immunity from prior infection and who remained unvaccinated, however, were the least likely to become re-infected.
A study completed in 2022 found that within 150 days, the effectiveness of the Moderna COVID-19 turned negative against the Omicron BA.2, BA.4, and BA.5 subvariants. Additionally, the study also found that against the Omicron BA.1.12.1, the vaccine turned negative within 91 days. Negative effectiveness means that a vaccinated individual is more likely to contract the virus. The study, which was conducted by researcher from Moderna and Kaiser Permanente, also found that persons who received three vaccine doses were more likely to become infected than those who only received two doses.
A study published in the CDC’s Morbidity and Mortality Weekly Report (MMWR) in November 2022 reported that the bivalent COVID-19 vaccines were less than 50 percent effective at preventing symptomatic COVID-19 illness. For individuals 65 years and older, the bivalent booster vaccine was reported to be only 32 percent effective in persons who received two primary doses. In those who received two primary doses and a monovalent booster before receipt of the bivalent booster, the effectiveness was only 19 percent. The bivalent vaccine was reported to be only slightly more effective in younger populations, but remained under 50 percent. This CDC sponsored study did not study the effects of the bivalent booster against severe disease, hospitalization, or death.
Two studies conducted in the U.S. and released in late 2022 found that vaccinated individuals were more likely to develop COVID-19 infections. One of the studies, found that the likelihood of COVID-19 infection increased with each subsequent dose and that unvaccinated individuals were least likely to become infected with COVID-19.
