Dual-indication bivalent RSV vaccine now available in HK: Maternal immunization data

Respiratory syncytial virus (RSV) prefusion F protein–based (RSVpreF) vaccine, a single-dose bivalent vaccine against RSV A and RSV B, is now available in Hong Kong for prevention of lower respiratory tract disease (LRTD) and severe LRTD caused by RSV in infants from birth up to 6 months of age through active immunization of pregnant individuals at a gestational age of 32–36 weeks, and for prevention of LRTD caused by RSV in individuals aged ≥60 years.

The RSVpreF vaccine is currently the first and only bivalent RSV vaccine with a dual indication in Hong Kong. [https://www.pfizer.com.hk/en/news-en/pfizer%E2%80%99s-first-dual-indication-vaccine-for-respiratory-syncytial-virus-rsv-is-available-this-month-in-hong-kong/; RSVpreF vaccine Hong Kong Prescribing Information, March 2024] Approval of its maternal immunization indication (immunization of pregnant individuals at a gestational age of 32–36 weeks in Hong Kong) is based on results of the phase III, double-blind, randomized, placebo-controlled MATTISE study conducted in 18 countries. [N Engl J Med 2023;388:1451-1464]

In the study, 7,357 pregnant individuals aged ≤49 years (median, 29 years) at a gestational age of 24–36 weeks (median, 31.3 weeks) received a single intramuscular injection of the RSVpreF vaccine (120 μg; n=3,682) or placebo (n=3,675). Overall, 12.5 percent of the maternal participants were Asian.

The primary efficacy endpoints were medically attended severe RSV-associated LRTD^* and medically attended RSV-associated LRTD^# in infants within 90, 120, 150 and 180 days after birth, which were assessed in 7,128 infants (RSVpreF vaccine group, n=3,570; placebo group, n=3,558). A lower boundary of confidence interval (CI) for vaccine efficacy (99.5 percent CI at 90 days; 97.58 percent CI at later intervals) >20 percent was considered to meet the success criterion for vaccine efficacy with respect to the primary endpoints.

Protects infants against medically attended RSV-associated LRTD
At prespecified interim analysis of efficacy (data cut-off, 30 September 2022), vaccine efficacy against medically attended severe RSV-associated LRTD in infants was:

• 81.8 percent (99.5 percent CI, 40.6–96.3 percent) at 90 days after birth;
• 73.9 percent (97.58 percent CI, 45.6–88.8 percent) at 120 days after birth;
• 70.9 percent (97.58 percent CI, 44.5–85.9 percent) at 150 days after birth; and
• 69.4 percent (97.58 percent CI, 44.3–84.1 percent) at 180 days after birth. [N Engl J Med 2023;388:1451-1464]

Vaccine efficacy against medically attended RSV-associated LRTD in infants was:

• 57.1 percent (99.5 percent CI, 14.7–79.8) at 90 days after birth;
• 56.8 percent (97.58 percent CI, 31.2–73.5) at 120 days after birth;
• 52.5 percent (97.58 percent CI, 28.7–68.9) at 150 days after birth; and
• 51.3 percent (97.58 percent CI, 29.4–66.8) at 180 days after birth.

No safety signals in maternal or infant participants
In the study, no safety signals were detected in maternal participants or in infants and toddlers up to 24 months of age. The incidence of adverse events was similar between the vaccine and placebo groups within 1 month after injection in maternal participants (13.8 vs 13.1 percent) and within 1 month after birth in infant participants (37.1 vs 34.5 percent). [N Engl J Med 2023;388:1451-1464]

US CDC advice
The US Centers for Disease Control and Prevention (CDC) advised that the RSVpreF vaccine can be administered to pregnant individuals along with other vaccines recommended during pregnancy (eg, tetanus, diphtheria and pertussis [Tdap] vaccine, influenza vaccine, and COVID-19 vaccine), without regard to timing. Administration can be simultaneous (ie, same clinic day) or at any interval between vaccine products. [https://www.cdc.gov/vaccines/vpd/rsv/hcp/pregnant-people-faqs.html]