Explanation :
Correct Answer:  A) 1957

People born before 1957 are often assumed to be immune to measles. This assumption is based on the high likelihood that they were exposed to the measles virus naturally, before the measles vaccine became widely available in 1963. Prior to the introduction of the vaccine, measles was so common that nearly all individuals were exposed to the virus, leading to natural immunity. This is supported by epidemiological data indicating that outbreaks of measles were widespread and frequent, which contributed to the natural immunization of the population at that time.

Reference:
CDC. (2020). Measles (Rubeola). For Healthcare Professionals. https://www.cdc.gov/measles/hcp/index.html

Explanation :
Correct Answer:  A) Rash begins on the extremities and spreads centrally

Atypical measles syndrome (AMS) is characterized by a rash that typically starts on the extremities and then spreads centrally, which is a reverse pattern compared to the classic measles rash that usually begins on the face and spreads downward. Additionally, the rash in atypical measles can be more petechial or vesicular and is often associated with severe pain and swelling of the extremities. Patients with atypical measles may also experience high prolonged fever, and bilateral pulmonary nodules and hilar lymphadenopathy, distinguishing AMS from the typical presentation of measles. This unique presentation is due to a hypersensitivity reaction in individuals who were previously sensitized by the killed virus vaccine, which did not provide complete immunity and altered the immune response to subsequent natural measles virus infections.

Reference:
Cherry, J.D. (2009). Atypical Measles Syndrome: Pathogenesis and Management. In: Feigin and Cherry's Textbook of Pediatric Infectious Diseases (6th ed., pp. 2427-2433). Philadelphia, PA: Saunders Elsevier.

Explanation :
Correct Answer:  D) Exposure to a different strain of the measles virus than the one included in the vaccine

Modified measles typically results from an attenuated infection in individuals with some level of partial immunity, which can be due to factors such as having maternal antibodies from a vaccinated mother (A), receipt of immunoglobulin (B), or receiving an incomplete series of the MMR vaccine (C). These situations can lead to a milder form of measles due to the body's partial ability to fight off the virus.

However, exposure to a different strain of the measles virus than the one included in the vaccine (D) is not a recognized risk factor for developing modified measles. The measles virus is monotypic, meaning that only one serotype exists, and the vaccine is effective against all circulating strains. Therefore, the concept of being exposed to a different strain as a risk factor for modified measles is incorrect. The measles vaccine provides immunity that is broad and effective against all strains of the measles virus, making this option the incorrect answer in the context of risk factors for modified measles.

Reference:
World Health Organization. (2019). Measles vaccines: WHO position paper – April 2017. Weekly Epidemiological Record, 92(17), 205-227.

Explanation :
Correct Answer:  D) Adults born before 1957 without any documentation of immunity

Generally, U.S. adults born before 1957 are considered to have been naturally exposed to measles and are presumed to have immunity due to the high prevalence of the disease before the vaccine was widely available. This assumption applies unless they are part of a high-risk group, such as healthcare workers, where proof of immunity might be required regardless of age. For the general population not in high-risk settings, being born before 1957 is often considered sufficient for presuming immunity, even without specific documentation. Therefore, adults born before 1957 without any documentation of immunity (D) typically do not need to receive another dose of the measles vaccine, in contrast to healthcare workers (A), students in post-secondary education (B), and international travelers (C) without evidence of immunity, who are recommended to be vaccinated 2 doses of MMR vaccine, separated by at least 28 days.

Reference:
Centers for Disease Control and Prevention (CDC). "Measles (Rubeola) for Healthcare Professionals." https://www.cdc.gov/measles/hcp/index.html

Explanation :
Correct Answer:  A) 4 weeks

The minimum interval between the first and second doses of the MMR (measles, mumps, and rubella) vaccine is 4 weeks (28 days). The Centers for Disease Control and Prevention (CDC) recommends that the second dose of MMR be given at least 28 days after the first dose. This interval is based on immunologic studies that indicate an improved response to the vaccine and a higher likelihood of long-term immunity when the second dose is given no earlier than 4 weeks after the first dose.

Reference:
CDC. (2019). Measles, Mumps, and Rubella (MMR) Vaccination: What Everyone Should Know. https://www.cdc.gov/vaccines/vpd/mmr/public/index.html

Explanation :
Correct Answer:  A) Cell-mediated immunity

Cell-mediated immunity plays a crucial role in the elimination of the measles virus during an infection. While humoral immunity (antibody-mediated) is important for neutralizing free viral particles and preventing their spread, cell-mediated immunity, particularly the function of T cells, is critical for the clearance of virus-infected cells. This cellular immune response is essential for the recovery from measles and contributes to the long-lasting immunity against the virus.

Reference:
Griffin, D.E. (2010). Measles Virus-Induced Suppression of Immune Responses. Immunological Reviews, 236(1), 176-189.

Explanation :
Correct Answer:  D) B and C only

For individuals exposed to measles who do not have evidence of immunity, the recommended post-exposure prophylaxis includes the administration of the MMR (measles, mumps, and rubella) vaccine within 72 hours of exposure and/or immunoglobulin (IG) within 6 days of exposure, depending on the individual's age, health status, and specific circumstances surrounding the exposure. Oral antiviral medications are not typically recommended for measles post-exposure prophylaxis. The vaccine and immunoglobulin should not be given concomitantly.

Reference:
Centers for Disease Control and Prevention (CDC). "Measles, Mumps, and Rubella -- Vaccine Use and Strategies for Elimination of Measles, Rubella, and Congenital Rubella Syndrome and Control of Mumps: Recommendations of the Advisory Committee on Immunization Practices (ACIP)." MMWR, 1998; 47(RR-8):1-57.