Questions and Answers about the New COVID-19 Bivalent Booster

Written By: Dr Winnie Chui

There have been many different COVID variants since 2019. With the most recent one, the Omicron variant (also known as BA.1), mRNA vaccines are being updated to protect people against the newest variant of concern, BA.4 and BA.5. These vaccines are called the bivalent COVID-19 vaccine and also may commonly refer to as the Omicron COVID-19 boosters.

1. What is COVID-19 bivalent booster vaccine?

It is a mRNA COVID-19 vaccine that protects against original SARS-CoV2 and its 2 highly contagious Omicron subvariants, BA.4 and BA.5 (hence the term “bivalent”). Whereas previous COVID-19 vaccine is monovalent and only protects against the original virus. Both the monovalent and bivalent vaccines target the spike protein of the virus. BA.4 and BA.5 are the currently circulating lineage of COVID-19 virus, particularly BA.5 as the dominant strain in many parts of the world right now. The only FDA authorized COVID vaccines with the updated bivalent formulation are from Pfizer-BioNtech and Moderna.

2. Why do we need an updated booster vaccine?

The concept is similar to those of the flu vaccine. As flu virus evolves, flu vaccine gets updated accordingly without requiring a full efficacy clinical trial.

While original mRNA COVID-19 vaccines continue to provide good protection against severe COVID-19 outcomes, including severe illness, hospitalization and death, they may have reduced effectiveness against symptomatic illness from Omicron variant, including BA.1, BA.4 and BA.5 subvariants. This is because Omicron is the most distinct variant of concern to date, with a number of key mutations distinguishing it from the original SARS-CoV2 virus.

Latest research study on the effectiveness of bivalent COVID-19 vaccine done by the US Centers for Disease Control and Prevention suggested that the vaccine can provide additional protection against COVID-19 infection compared with previous vaccination with 2, 3, or 4 monovalent vaccines. The data showed that the vaccine effectiveness among those between the age of 18 to 49 receiving the bivalent booster, compared to those with more than two shots of the original vaccine only, ranged from 30% to 56% (depending on if their last dose of original vaccine was 3 months ago or more than 8 months ago). And the vaccine effectiveness was lower for older population (age 50 and above), ranging from 28% to 48%. The benefit of the bivalent vaccine seems to increase with the duration since the last original vaccine dose, yet without much difference in terms of the number of previous original vaccine. In other words, the bivalent vaccine has shown to have the ability to replenish waning level of antibodies.

3. Should I get boosted if I’ve already had COVID-19 infection?

Previous COVID-19 infection can provide some immunity. However, that immunity wanes quickly so getting the booster shot can give you additional protection. CDC recommends people who have recovered from COVID-19 infection to delay the bivalent booster by at least 3 months.

4. Do I need to get the bivalent vaccine if I just had the original mRNA COVID-19 vaccine recently as my booster shot? 

Original mRNA COVID-19 vaccines are still recommended for use as the COVID-19 primary series. According to COVID-19 vaccine schedule in Hong Kong, for those who have had their booster shot (3rd dose) with the original vaccine, they may consider having the bivalent booster (4th dose) at least 6 months apart.

Starting from December 16, for persons aged 18 or above and who had received four doses (or recovered adults who had received three doses with the last dose or recovery being more than six months ago), they may choose to receive an additional dose of vaccine (either original vaccine or bivalent booster) for additional protection. Appointments can be made online starting on December 16 and receive the dose on same day. See below for further information on vaccine appointment booking.

5. What are the side effects? 

The bivalent booster was developed based on existing mRNA COVID-19 vaccines. Similar to the original mRNA COVID vaccines, bivalent vaccines may have common side effects such as fatigue, headache, muscle and joint aches, and fever. Experts do not anticipate any differences in safety profile as the changes are not significant enough from the original vaccine.

6. Can I get both a COVID booster and flu shot at the same time?

It is safe to get both the flu shot and any COVID vaccine at the same time.

7. Is it possible for me to get the COVID-19 Bivalent Vaccine in Hong Kong?

The Hong Kong Government currently offers the COVID-19 Bivalent Vaccine as of December 2nd, 2022. You can book for your COVID-19 booster in the Hong Kong Government COVID-19 Vaccination Portal here.

If you have any additional questions, we recommend speaking to your doctor for more information and to see your suitability for the vaccine.