** Shares of drug developer Atea Pharmaceuticals Inc
AVIR.O down 6.2% at $4.39 in early trade
** Co says board of directors unanimously rejected buyout
proposal from Concentra Biosciences
** Says the proposal undervalues co
** AVIR's shares had risen 37% on receiving buyout offer
from Concentra last week; financial terms of the offer were not
disclosed
** Concentra Biosciences is an affiliate of investment firm
Tang Capital Partners; Tang Capital owns 3.6% of AVIR
** AVIR's stock down 4.4% YTD
(Reporting by Aditya Samal)
((Aditya.Samal@thomsonreuters.com;))