A recent analysis published in JAMA Network Open has suggested that COVID-19 vaccine effectiveness against the omicron variant significantly decreases after six months for individuals who have only received their primary series. This decline in efficacy may not be entirely representative of the situation in the United States as the study included various vaccines used globally, such as Pfizer-BioNTech, Moderna, AstraZeneca, and Sinovac, but did not take into account the updated bivalent vaccines targeting the original strain and subvariants of omicron. Nonetheless, experts emphasize that vaccines remain effective in significantly reducing the risk of hospitalization and death. Protection against symptomatic disease decreased gradually from 52.8% one month after the last dose to 8.9% at nine months. Similarly, vaccine effectiveness against overall infection declined from 44.4% to 13.4% at the same intervals. However, vaccines such as Pfizer and Moderna exhibited higher effectiveness compared to AstraZeneca and Sinovac. Recently, studies by the Centers for Disease Control and Prevention (CDC) have shown that updated bivalent boosters enhance the level of protection against COVID-19 variants. The booster slashed the risk of visiting a hospital due to COVID-19 by at least 50% for U.S. adults in one study, while another showed its additional protection in those who received two to four doses of the original vaccine against symptomatic infection with two variants of omicron currently circulating. The analysis noted that vaccine effectiveness increased upon receiving the original booster dose but gradually waned over time against infection and symptomatic disease. Therefore, while the effectiveness of vaccines against omicron infection may wane over time, vaccines still provide significant protection against severe disease, hospitalization, and death. It is noteworthy that the latest CDC data reveals COVID-19 cases and death rates among vaccinated individuals, with and without the updated booster, significantly lower than those unvaccinated.
