From the Guidelines
Yes, an individual with a low antibody titer against measles can still be immune to measles. Immunity to measles involves both antibody-mediated (humoral) and cell-mediated immune responses. While antibody titers are commonly used to assess immunity, they don't tell the complete story. Some individuals maintain protective immunity through memory B cells and T cells even when circulating antibody levels have declined to low or undetectable levels. This cellular immunity can rapidly produce new antibodies upon re-exposure to the virus. According to the study by 1, evidence indicates that waning immunity is not a major cause of vaccine failure and has little influence on measles transmission. Additionally, revaccination of children who have low levels of measles antibody produces only a transient rise in antibody levels. Key points to consider include:
- Immunity to measles is not solely dependent on antibody titers
- Cell-mediated immune responses, such as memory B cells and T cells, can provide protective immunity even with low antibody levels
- The second dose of MMR vaccine is recommended to reduce primary vaccine failure, rather than to address waning immunity
- Revaccination may not be necessary for individuals with low antibody titers, unless they are at high risk of exposure. It is essential to consult with a healthcare provider to interpret specific antibody results in the context of vaccination history and risk factors.
From the Research
Measles Immunity and Antibody Titer
- An individual with a low antibody titer against measles may still be immune to measles, as the level of immunity is not solely determined by the antibody titer 2.
- A study found that subjects with an EIA-IgG titer of ≥ 12.0 may be protected against measles, while those with a titer of 4.0 to 8.0 may be protected insufficiently and require a booster dose 2.
- Another study found that the measles-neutralizing antibody titers of individuals who had natural infection were significantly higher than those who received one or two booster doses of the MMR vaccine 3.
Factors Affecting Measles Immunity
- The avidity of measles-specific IgG antibodies may affect susceptibility to measles virus infection in some vaccinated individuals 4.
- A study found that the presence of moderate and severe chronic graft-versus-host disease (GVHD) was associated with more rapid loss of immune protection against measles 5.
- Prior immunization with measles, mumps, and rubella vaccines may contribute to the antibody response to COVID-19 antigens, with measles vaccination triggering cross-reactive B cells 6.
Antibody Titer and Immunity
- The level of antibody titer does not always correlate with the level of immunity, as other factors such as the avidity of antibodies and the presence of cell-mediated immunity also play a role 2, 4.
- A low antibody titer does not necessarily mean that an individual is not immune to measles, as the immune system has multiple mechanisms to protect against infection 3, 5.