2015 Employee Benefits Overview

2015 Employee Benefits Overview ALNYLAM 2015 EMPLOYEE BENEFITS OVERVIEW 1

Offering a robust Benefits Program is an integral part to Alnylam s culture of investing in its employees health and well-being. We continually review our benefit offerings to ensure we keep pace with the market and meet the needs of our growing employee population. We are a company positioned for tremendous growth and investing in our employees is crucial to our success and ultimately to helping our patients lead better lives. This brochure provides a brief summary of the benefits available to regular employees. 2 ALNYLAM 2015 EMPLOYEE BENEFITS OVERVIEW

Health MEDICAL INSURANCE* Blue Cross Blue Shield Blue Care Elect Preferred PPO www.bluecrossma.com The Company pays 90% of premium costs $20 co-pay for office visits $100 emergency room co-pay Out of network services covered at 80% after deductible is reached Deductible of $250 per individual, $500 per family per calendar year Out of pocket maximum of $1,250 per individual, $2,500 per family per calendar year, including deductible and co-insurance Prescription co-pay of $15/30/50 DENTAL INSURANCE* Delta Dental PPO Plus Premier www.deltamass.com The Company pays 90% of premium costs Preventative: 100% coverage (no deductible) Basic Restorative: 80% coverage (after deductible) Major Restorative: 50% coverage (after deductible) Annual Deductible Preventative: None Basic & Major: $50 per person /$150 per family per calendar year $1,500 maximum per family member per calendar year VISION INSURANCE* EyeMed Vision Care www.eyemedvisioncare.com Eye exams every 12 months with a $10 co-pay Prescription glasses lenses every 12 months with a $25 co-pay Contact lenses every 12 months with a $130 allowance and 15% off the balance Frames every 12 months with a $130 allowance and 20% off the balance Laser Vision correction every 24 months with a 15% discount off the retail price or a 5% discount off the promotion price Alnylam covers 50% of the cost of this benefit FLEXIBLE SPENDING ACCOUNTS Discovery Benefits www.discoverybenefits.com Eligible on first day of employment for all regular employees Employee pays 100% of this benefit on a pre-tax basis. Ability to pay for certain medical and dependent care expenses with pre-tax dollars Medical Care maximum deduction is $2,550 annually Dependent Care maximum deduction is $5,000 annually per household. EMPLOYEE ASSISTANCE PLAN Kathleen Greer Associates https://kga.com or toll free at 1-800-648-9557 Eligible on first day of employment Provides professional and confidential counseling to individual employees and their household members, as well as consultation, training and organizational development services to managers and supervisors. Available 24 hours a day, 7 days a week FITNESS BENEFIT Cambridge Racket and Fitness Club www.cambridgefitness.com BodyScapes Fitness www.bodyscapesfitness.com * See Appendix The Company contributes $30/month towards monthly membership. Discount on membership rates and enrollment fee. ALNYLAM 2015 EMPLOYEE BENEFITS OVERVIEW 1 OR The Company will reimburse up to $360 per calendar year As an alternative, employees may choose their own qualified health club and submit for an equivalent reimbursement ($360) once per calendar year

Income Protection LIFE INSURANCE/AD&D Unum www.unum.com The Company pays 100% of the cost of this benefit. Basic Benefit equal to two times basic annual salary Up to $900,000 maximum, with approved statement of good health required for amounts over $500,000 SUPPLEMENTAL LIFE INSURANCE PLAN Unum www.unum.com Employee pays 100% of this benefit on a posttax basis. Option to purchase additional life insurance coverage for employee, spouse, and children Coverage is in addition to company provided coverage Payment through payroll deduction SHORT TERM DISABILITY Unum www.unum.com The Company pays 100% of the cost of this benefit. Benefits payable after 7 day elimination period and approval of claim by Unum Benefits payable at 100% of weekly earnings Maximum period of 12 weeks LONG TERM DISABILITY Unum www.unum.com The Company pays 100% of the cost of this benefit. Benefits payable after 90 day elimination period or the end of STD coverage and approval of claim by Unum Provides 60% of monthly earnings to a maximum benefit of $15,000 per month Financial Growth SAVINGS & INVESTMENT PLAN 401(K) PLAN Fidelity www.netbenefits.com Eligible on first day of employment for all regular employees Employee pays 100% of the contribution. The Company pays 100% of the match. Employees may contribute up to 15% of pre-tax earnings or a maximum of $18,000 per year for 2015 ($24,000 for employees age 50 or over). Discretionary match of up to 50% of the first 6% (3%) of employee contributions to a maximum of $5,250 STOCK OPTION PLAN Eligible on first day of employment for all regular employees The company has reserved a designated number of shares of its common stock for issuance to employees under the Alnylam Pharmaceuticals, Inc. Incentive Stock Option Plan. More details available upon employment. 2 ALNYLAM 2015 EMPLOYEE BENEFITS OVERVIEW

Financial Growth (continued) EMPLOYEE STOCK PURCHASE PLAN For employees hired prior to August 1 st of the current year, the next entry date is November 1 st of the current year For employees hired after August 1 st of the current year, the next entry date is May 1 st of the following year Opportunity to purchase shares of Alnylam common stock at a discount through payroll deduction Ability to withhold up to 15% of base salary to purchase Alnylam Common Stock at 85% of the lower of (1) the fair market value per share of Common Stock on your Entry Date, or (2) the fair market value per share on the annual purchase date. Please see HR for details Paid Time Off VACATION TIME Eligible immediately upon employment if hire date is on or prior to the 15th of the month. Eligible on first day of first full month of employment if hire date is after the 15th of the month. Full-time regular employees accrue 15 days per year, accruing at the end of the month at the rate of 1.25 days per month (10 hours) After 5 years at Alnylam, Full-time regular employees accrue 20 days per year, accruing at the end of the month at the rate of 1.67 days per month (13.33 hours) Part-time employees scheduled to work over 20 hours per week will accrue prorated vacation time at the end of each month. Maximum accrual of 15 days at any time until 5 years of employment when maximum accrual is 20 days. SICK TIME Eligible on first day of employment Regular, full-time employees are eligible for up to 6 days per year. Part-time employees scheduled to work over 20 hours per week will be eligible for sick time on a pro-rated basis. Carry over unused sick time up to the maximum total of 10 days. MATERNITY LEAVE Eligible on first day of employment Eligible for 8 weeks of full paid leave With an additional 4 weeks of unpaid leave. Please see HR for details PATERNITY LEAVE Eligible on first day of employment Eligible for 2 weeks of full paid leave. Please see HR for details HOLIDAYS Eligible immediately upon employment for scheduled holidays Employees joining prior to July 1 are eligible for the floating holiday The Company observes 11 paid holidays per year (10 scheduled and 1 floating holiday) New Year s Day Martin Luther King Jr. Birthday Presidents Day Memorial Day Independence Day Labor Day Columbus Day Thanksgiving Day Day after Thanksgiving Christmas ALNYLAM 2015 EMPLOYEE BENEFITS OVERVIEW 3

Work/Life TRANSPORTATION PROGRAM Eligible on first day of employment T-Pass Program: Alnylam will provide a pass for transit to the Kendall Square or Alewife T-stop. The Company pays 100% of the cost of this benefit. OR Subsidized Parking: Alnylam will subsidize the monthly cost of a parking permit. The Company pays 75% for VP s and 90% for all other employees. OR Bike/Walk: Alnylam will add a benefit of $20.00/ month directly to your semi-monthly pay. GUARANTEED RIDE HOME Employees must pre-register and only available to those who carpool, vanpool, bike, walk, or take transit at least two days per week It encourages the use of alternatives to driving alone by ensuring that if there is an emergency during the day, you will not be stranded at work. Career Growth TUITION REIMBURSEMENT The Company pays 100% of the cost of this benefit. Reimbursement for pre-approved courses with a minimum grade of C (undergraduate) or B (graduate). Courses must be related to one s current job, or be part of a job-related degree or certificate program. Alnylam will reimburse 100% for pre-approved courses including tuition, books and required fees. These benefits reflect our commitment to foster a culture of caring and enable our employees to achieve success at home and at work. 4 ALNYLAM 2015 EMPLOYEE BENEFITS OVERVIEW

Employee Discounts COMPUTER/TECHNOLOGY DISCOUNTS (FOR HOME USE) Dell Employee Purchase Program - Discount on Dell Computers through the Employee Purchase program. www.dell.com/epp CDW Employee Purchase Program Discount on technology products and accessories. www.cdw.com/epp CELL PHONE DISCOUNTS AT&T Verizon Discount on wireless monthly fees if you sign up using your company e-mail SELECTPLUS+ SITTERCITY AND YEARS AHEAD www.selectplus.com/alnylam This membership provides access to online caregiver profiles including, nannies, babysitters, pet sitters, elder care, and housekeeping/housesitting services. DECORDOVA ART MUSEUM www.decordova.org This membership provides free unlimited admission (with presentation of company ID) to the Museum for all employees and immediate family members, in addition to the benefits listed below. Priority registration and Member discount at the Museum School 10% discount on all merchandise at The Store @ decordova 10% discount at The Café @ decordova 20% discount on gallery rental fee (Mon-Thurs) ZIPCAR FOR BUSINESS The Zipcar for Business benefit reduces the annual fee from $60 to $25. Also includes discounted driving rates. FEDEX OFFICE FedEx Office discounts are listed below. 30% off black and white copies 30% off color copies 10% off other production services AMUSEMENT PARKS Discounts to Six Flags New England, Water Country and Canobie Lake Park. KIMPTON HOTELS www.kimptonhotels.com The Kimpton Global Business program gives a 10% discount off the best available rate for Alnylam Employees. RESTAURANTS Fuji at Kendall http://www.fujiatkendall.com/ Champions http://www.championscambridge.com/ Fuji Restaurant Kendall Square, located on the ground floor at 300 Third Street, gives a 10% discount to Alnylam employees. AND Champions - The restaurant at the Cambridge Marriott Hotel, gives 10% off for all Alnylam Pharmaceuticals employees ALNYLAM 2015 EMPLOYEE BENEFITS OVERVIEW 5

Details may change without notice. ALNYLAM 2015 EMPLOYEE BENEFITS OVERVIEW 7