B/MASSACHUSETTS/2/2012-LIKE STRAIN USED B/MASSACHUSETTS/2/2012 WILD TYPE

Table of contents

• What is B/Massachusetts/2/2012-like strain?
• How does B/Massachusetts/2/2012-like strain work?
• Which conditions is it used or studied for?
• How is B/Massachusetts/2/2012-like strain given?
• What do the clinical trials show?
• What side effects are known?

What is B/Massachusetts/2/2012-like strain?

B/Massachusetts/2/2012-like strain is a laboratory reference strain of influenza B virus, specifically from the B/Yamagata lineage. The full name is B/MASSACHUSETTS/2/2012-LIKE STRAIN USED B/MASSACHUSETTS/2/2012 WILD TYPE. In vaccine production, the wild-type virus is used to create inactivated vaccine components that teach the immune system to recognise and fight this particular influenza B strain.^[2]

Influenza B viruses are divided into two main lineages: B/Victoria and B/Yamagata. The B/Massachusetts/2/2012 strain belongs to the B/Yamagata lineage and was included in seasonal influenza vaccines for several northern hemisphere seasons, including 2013/2014.^[2]

How does B/Massachusetts/2/2012-like strain work?

When the inactivated influenza vaccine containing this strain is injected, the immune system encounters viral proteins from the B/Massachusetts/2/2012-like virus. Because the virus is inactivated, it cannot cause infection. Instead, the immune system learns to recognise the viral surface proteins, particularly hemagglutinin, and produces antibodies against them.^[2]

These antibodies circulate in the blood and can bind to the real influenza B virus if the person is later exposed. This binding neutralises the virus and prevents it from infecting cells. The strength of this immune response is measured in clinical trials using hemagglutination inhibition (HI) tests, which detect how well antibodies block the virus from binding to red blood cells, and microneutralization tests, which measure how well antibodies prevent the virus from infecting cells in the laboratory.^[1]

Which conditions is it used or studied for?

• Influenza — a contagious respiratory illness caused by influenza viruses, including influenza B strains like B/Massachusetts/2/2012.
• Immunity against influenza — the protection the body develops after vaccination or natural infection, measured by antibody levels in the blood.

How is B/Massachusetts/2/2012-like strain given?

The strain is delivered as part of an inactivated influenza vaccine. In the clinical trial, the vaccine was administered as a 0.5 ml intramuscular injection. The vaccine formulation was described as inactivated, split virus or surface antigen, meaning the virus particles are broken apart or only surface proteins are used, making the vaccine safe for use.^[1]

The supplementary source describes a trivalent inactivated influenza vaccine for the 2013/2014 northern hemisphere season, which contained surface antigens from three influenza strains, including a B/Massachusetts/2/2012-like strain.^[2]

What do the clinical trials show?

Which trial studied this strain?

One completed Phase 3 clinical trial (NCT03323112) investigated immune responses in 1,500 health care personnel who received an inactivated influenza vaccine containing the B/Massachusetts/2/2012-like strain.^[1] The trial was interventional, meaning participants received the vaccine and were followed over time to measure outcomes.

What did the trial measure?

The primary outcome was humoral immunity — the antibody response in the blood — against influenza virus strains included in the vaccines of the current and past seasons, as well as circulating influenza strains. Antibody levels were assessed from serum samples collected before and after vaccination using traditional hemagglutination inhibition (HI) tests, with microneutralization or neutralization tests also used when needed.^[1]

Who took part in the trial?

The trial enrolled health care personnel, a group at higher risk of exposure to influenza and important for maintaining health services during influenza seasons. A total of 1,500 participants were enrolled. The trial status is completed, meaning the study has finished and results may be available in the registry record.^[1]

What side effects are known?

The supplementary source describes an open-label, uncontrolled study of a trivalent inactivated influenza vaccine for the 2013/2014 northern hemisphere season, which assessed immunogenicity and safety. The source title indicates that safety was evaluated, but the provided content does not list specific side effects. Therefore, no detailed side effect information can be reported from the available sources.^[2]