The COVID-19 pandemic continues to evolve, and vaccination remains a primary public health strategy. As the SARS-CoV-2 virus changes, vaccine developers adapt formulations to maintain effectiveness against new variants. These advancements aim to provide protection against severe illness and reduce virus spread. Understanding updated vaccines is important for informed health decisions.
Understanding Bivalent Vaccines
A bivalent vaccine targets two different components or strains of a virus, offering broader protection than earlier vaccine versions. For COVID-19, this means the vaccine contains genetic material that instructs the body to produce an immune response against the original SARS-CoV-2 strain and specific newer Omicron subvariants. Initial COVID-19 vaccines were “monovalent,” targeting only the original strain identified in 2019.
This dual-target approach allows the immune system to recognize and fight off both the original virus and more recent, highly transmissible variants. For example, some bivalent formulations have targeted the original strain alongside the Omicron BA.4 and BA.5 subvariants, or later, the XBB.1.5 subvariant. This design provides a more comprehensive defense against the evolving viral landscape.
The Need for Updated Protection
Viruses, including SARS-CoV-2, undergo continuous mutation, leading to the emergence of new variants. The Omicron variant and its sublineages demonstrated a significant shift in the virus’s characteristics. These newer variants evolved to be more transmissible and, in some cases, partially evade immunity from earlier vaccines or previous infections.
Original COVID-19 vaccines, while effective against severe disease, became less potent against symptomatic infection caused by these new Omicron variants due to immune evasion. To counter this, bivalent vaccines were developed to provide broader and more effective protection. By including components from both the original strain and dominant Omicron subvariants, these updated vaccines elicit a stronger immune response against currently circulating strains. This adaptation is similar to how influenza vaccines are updated annually to address circulating flu strains.
Benefits and What to Expect
Receiving a bivalent vaccine offers improved protection against severe illness, hospitalization, and death from currently circulating COVID-19 variants. Studies show that bivalent booster doses provide additional protection against symptomatic SARS-CoV-2 infection in individuals who previously received only monovalent vaccines. For instance, one study in adults aged 65 and older found vaccine effectiveness of 72% against hospitalization and 68% against death.
After receiving a bivalent vaccine, individuals may experience common, mild side effects. These reactions include pain, redness, or swelling at the injection site. Other common systemic effects can involve fatigue, headache, muscle aches, fever, and chills. Most side effects are temporary and resolve within a day or two.
Current Recommendations
Public health recommendations for COVID-19 vaccination are regularly updated by health authorities such as the Centers for Disease Control and Prevention (CDC). While bivalent vaccines were previously recommended, updated monovalent vaccines targeting dominant Omicron subvariants like XBB.1.5 are now recommended for initial vaccination series or as booster doses for various age groups and individuals with certain risk factors. For example, the CDC’s Advisory Committee on Immunization Practices recommended updated 2023–2024 XBB.1.5 COVID-19 vaccination for all persons aged 6 months and older.
These updated vaccines provide protection against currently circulating lineages. Individuals aged 5 years and older receive a single updated dose, while children from 6 months to 4 years may require one or three doses depending on their prior vaccination status or COVID-19 history. Consult local health authorities or a healthcare provider for the most current and personalized guidance specific to one’s region and health status.