| CUSIP No. 92529L102 | 13D | Page 1 7 of 19 Pages |
EXHIBIT 99.2
POWER OF ATTORNEY
KNOWN ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and appoints CRAIG L. SLUTZKIN as his true and lawful attorney-in-fact and agent for him and in his name, place and stead, in any and all capacities, to sign any and all documents relating to any and all Securities and Exchange Commission filings which may be required, granting unto said attorney-in-fact and agent full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he might or could do in person, thereby ratifying and confirming all that said attorney-in-fact may lawfully do or cause to be done by virtue hereof.
This power shall continue in effect until terminated in writing.
| By: | /s/ Vijay K. Lathi | |
| Vijay K. Lathi |
Dated: October 5, 2005
| CUSIP No. 92529L102 | 13D | Page 18 of 19 Pages |
POWER OF ATTORNEY
KNOWN ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and appoints CRAIG L. SLUTZKIN as his/her true and lawful attorney-in-fact and agent for him/her and in his/her name, place and stead, in any and all capacities, to sign any and all documents relating to any and all Securities and Exchange Commission filings which may be required, granting unto said attorney-in-fact and agent full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he/she might or could do in person, thereby ratifying and confirming all that said attorney-in-fact may lawfully do or cause to be done by virtue hereof.
This power shall continue in effect until terminated in writing.
| By: | /s/ Philippe O. Chambon | |
| Philippe O. Chambon | ||
| By: | /s/ Jeani Delagardelle | |
| Jeani Delagardelle | ||
| By: | /s/ Ronald Hunt | |
| Ronald Hunt | ||
Dated: September 29, 2006
| CUSIP No. 92529L102 | 13D | Page 19 of 19 Pages |
POWER OF ATTORNEY
KNOWN ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and appoints CRAIG L. SLUTZKIN as his true and lawful attorney-in-fact and agent for him and in his name, place and stead, in any and all capacities, to sign any and all documents relating to any and all Securities and Exchange Commission filings which may be required, granting unto said attorney-in-fact and agent full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he might or could do in person, thereby ratifying and confirming all that said attorney-in-fact may lawfully do or cause to be done by virtue hereof.
This power shall continue in effect until terminated in writing.
| By: | /s/ Liam Ratcliffe | |
| Liam Ratcliffe |
Dated: April 9, 2012
