Note 12 - Segment Reporting - Schedule of Segment Reporting Information, by Segment (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2026	Mar. 31, 2025
Revenues		$ 39,227	$ 20,876
Research and Development Expense		29,413	30,744
General and administrative		4,641	5,067
Interest income		(551)	(437)
Non-cash interest expense related to sale of future royalties		505	997
Income Tax Expense (Benefit)		29	95
Net income (loss)		5,179	(15,591)
Adjustments and reconciling items		5,179	(15,591)
Net income (loss)		5,179	(15,591)
Operating Segments [Member]
Revenues		39,227	20,876
General and administrative		4,641	5,067
Interest income		(551)	(437)
Non-cash interest expense related to sale of future royalties		505	997
Other segment items(A)	[1]	11	1
Income Tax Expense (Benefit)		29	95
Net income (loss)		5,179	(15,591)
Adjustments and reconciling items		5,179	(15,591)
Net income (loss)		5,179	(15,591)
Operating Segments [Member] | Norovirus Program [Member]
Research and Development Expense		48	1,556
Operating Segments [Member] | Covid-19 Program [Member]
Research and Development Expense		20,393	15,718
Operating Segments [Member] | Other Programs [Member]
Research and Development Expense		0	306
Operating Segments [Member] | Preclinical Research [Member]
Research and Development Expense		81	399
Operating Segments [Member] | Process Development Program [Member]
Research and Development Expense		0	46
Operating Segments [Member] | Internal Research and Development Costs [Member]
Research and Development Expense		8,891	12,719
Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment [Member]
Net income (loss)		0	0
Adjustments and reconciling items		0	0
Net income (loss)		$ 0	$ 0

[1] Other segment items included in other income (expense), net.