Pfizer Inc (NYSE:PFE) plans to raise $31 billion from a debt offering to finance its proposed acquisition of Seagen Inc (NASDAQ:SGEN) for $43 billion.

The debt offering, which would be in eight tranches, is expected to close on May 19.

Pfizer expects Seagen could contribute more than $10 billion in risk-adjusted revenues in 2030, with potential significant growth beyond 2030.

Tuesday, the FDA released briefing documents describing safety data for Pfizer's experimental respiratory syncytial virus (RSV) vaccine in pregnant women as "generally favorable."

The company is seeking approval to use the shot in pregnant women to protect newborns to six-month-old babies from lower respiratory tract disease (LRTD) and severe LRTD caused by respiratory syncytial virus (RSV).

If approved, it could become the first maternal vaccine against the virus.

The FDA is set to make an approval decision by August 21.

Pfizer's vaccine, RSVpreF, was 81.8% effective in preventing severe lower respiratory tract illness in infants in the first 90 days of life.

The shot was 69.4% effective in preventing severe infections in the first 180 days.

The FDA's analysis did note a numerically higher — but not statistically meaningful — amount of premature deliveries, making up 5.6% of the vaccinated group against 4.7% of the placebo group. 

Price Action: PFE shares are up 0.35% at $37.14 premarket on the last check Wednesday.