Forward-looking Statements This presentation contains forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995 regarding, among other things, the potential approval by the U.S. Food a

Corporate Presentation January

Forward-looking Statements This

presentation contains forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995 regarding, among other things, the potential approval by the U.S. Food and Drug Administration (FDA) of a New Drug Application (NDA)

for tebipenem HBr; the timing of launch of tebipenem HBr; future commercialization of tebipenem HBr; the potential number of patients who could be treated by tebipenem HBr and market demand for tebipenem HBr generally; the effectiveness of tebipenem

HBr and its potential impact on healthcare resource utilizations; expected broad access across payer channels for tebipenem HBr; the expected pricing of tebipenem HBr and the anticipated shift in treating patients from intravenous to oral

administration; the initiation, timing, progress and results of the Company's preclinical studies and clinical trials and its research and development programs, including management's assessment of such results; the direct and indirect

impact of the pandemic caused by an outbreak of a strain of coronavirus (COVID-19) on the Company's business and operations; the timing of the availability of data from the Company's clinical trials; the timing of the Company's

filings with regulatory agencies; product candidate benefits; competitive position; business strategies; objectives of management; potential growth opportunities; potential market size; reimbursement matters; possible or assumed future results

of operations; projected costs; and the Company's cash forecast and the availability of additional non-dilutive funding from governmental agencies beyond any initially funded awards. In some cases, forward-looking statements can be

identified by terms such as "may," "will," "should," "expect," "plan," "aim," "anticipate," "could," "intent," "target,"

"project," "contemplate," "believe," "estimate," "predict," "potential" or "continue" or the negative of these terms or other similar expressions. All

statements other than statements of historical facts contained in this presentation are forward-looking statements. The Company may not actually achieve the plans, intentions or expectations disclosed in these forward-looking statements.

Actual results or events could differ materially from the plans, intentions and expectations disclosed in these forward-looking statements as a result of various factors, including: any delays in review of the NDA submission by the FDA for any

reason or that the Physician Drug User Fee Act (PDUFA) date for the NDA review may be revised; the Company's need for additional funding; the lengthy, expensive, and uncertain process of clinical drug development; the Company's reliance

on third parties to manufacture, develop, and commercialize its product candidates, if approved; the ability to develop and commercialize the Company's product candidates, if approved; the Company's ability to re-initiate the Phase 2a

clinical trial of SPR720 for nontuberculous mycobacterial (NTM) pulmonary disease; the potential impact of the COVID-19 pandemic; the Company's ability to retain key personnel and to manage its growth; whether results obtained in preclinical

studies and clinical trials will be indicative of results obtained in future clinical trials and whether preliminary data from the Company's clinical trials will be predictive of final results from such trials; whether the

Company's product candidates will advance through the preclinical development and clinical trial process on a timely basis, or at all, taking into account such factors as the effects of possible regulatory delays, slower than anticipated

patient enrollment, manufacturing challenges, clinical trial design, clinical data requirements and clinical outcomes; whether the results of such clinical trials will warrant submission for approval from the FDA or equivalent foreign

regulatory agencies; decisions made by the FDA and equivalent foreign regulatory agencies with respect to the development and commercialization of the Company's product candidates; the commercial potential of the

Company's product candidates; the Company's ability to obtain adequate third-party reimbursement for its product candidates; whether the Company will satisfy all of the pre-conditions to receipt of the development milestone payments

under its agreements with Everest Medicines and certain entities managed by HealthCare Royalty Management, LLC (HCR); whether BARDA elects to exercise its second option under the Company's agreement with BARDA; the Company's ability to

implement its strategic plans; the Company's ability to obtain, maintain and enforce intellectual property and other proprietary rights for its product candidates; the risks and uncertainties related to market conditions; whether the

Company's cash resources will be sufficient to fund its continuing operations for the periods and/or trials anticipated; and other factors discussed in the "Risk Factors" section of the Company's periodic reports filed with

the U.S. Securities and Exchange Commission (SEC), and risks described in other filings the Company may make with the SEC in the future. The forward-looking statements included in this presentation represent the Company's views as of the

date of this presentation. The Company anticipates that subsequent events and developments will cause its views to change. However, while the Company may elect to update these forward-looking statements at some point in the future, it specifically

disclaims any obligation to do so. These forward-looking statements should not be relied upon as representing the Company's views as of any date subsequent to the date of this presentation.

Tebipenem HBr (previously SPR994): oral

carbapenem ADAPT-PO Phase 3 met its primary endpoint in landmark trial - Oral tebipenem HBr demonstrated noninferiority to IV ertapenem in cUTI and AP; safety results similar to intravenous ertapenem NDA accepted by FDA, with Priority

Review. PDUFA DATE: June 27, 2022 Pipeline of assets supported by positive Phase 1 data SPR720: First potential oral therapy for NTM infections; granted orphan designation SPR206: Novel therapy for MDR Gram-negative infections; Phase 1 BAL and renal

impairment trials initiated 2Q 2021 Multi-billion dollar opportunity for cUTI and NTM Large unmet needs in infectious disease No approved branded or generic oral competition within carbapenem class Marketed primarily outside the hospital Spero:

Robust Infectious Disease and Rare Disease Portfolio led by Oral Tebipenem HBr cUTI = complicated urinary tract infections; ancillary supportive studies also required for tebipenem HBr in addition to single Phase 3 trial; NTM =

non-tuberculous mycobacterial ; PK = Pharmacokinetic; MDR = multidrug resistant infections; Tebipenem HBr = tebipenem pivoxil hydrobromide (formerly SPR994)

Multiple Catalysts Across the Pipeline

Program Target Indication Preclinical Phase 1 Phase 2 Phase 3 Upcoming Milestone Partnerships/Alliances Oral Carbapenem for Gram Negative Multidrug Resistant (MDR) Infections Tebipenem HBr Complicated UTI (cUTI) NDA accepted for the

treatment of cUTI with Priority Review PDUFA Date: June 27, 2022 Oral DNA Replication Inhibitor for Non-tuberculous Mycobacterial (NTM) Disease SPR720 NTM FDA clinical hold lifted, Announced Jan 4, 2022 Planning for Phase 2a Trial restart in

2H 2022 Direct Acting IV Potentiator for Gram Negative MDR Infections SPR206 MDR Infections Phase 1 BAL and renal impairment trials initiated 2Q 2021; data readouts expected in early 2022 Positive Tebipenem HBr ADAPT-PO Phase 3 Topline

Data Support Accepted NDA Filing As of January 4, 2022

Spero Pipeline Assets Share Common

Attributes With Other Successful ID Drugs Non-DRG reimbursement High unmet need with strong economic benefit $1 B+ Sales* *Estimated Peak Year Worldwide Sales *Trademarks are properties of their respective owners

Oral Carbapenem Tebipenem

Tebipenem HBr: Positive ADAPT-PO Phase

3 Trial Results Robust Results Support NDA Submission and Potential Treatment Shift from IV to Oral in cUTI Positive results in landmark study unprecedented for the field Overall combined response rate: Oral tebipenem HBr response

rate of 58.8% versus 61.6% for IV ertapenem (-3.3%; -9.7, 3.2; -12.5% NI margin)* Tebipenem HBr safety results similar to ertapenem Landmark ADAPT-PO Trial Met Primary Endpoint Positive ADAPT-PO Trial Results Support an Accepted NDA Submission

Tebipenem HBr, if approved as the first oral carbapenem, could allow appropriate patients the opportunity to receive treatment in the community setting Provides an important value proposition that could benefit patients, hospitals and payers If

approved, tebipenem HBr would be the only oral carbapenem approved for treatment of complicated urinary tract infections (cUTI) and acute pyelonephritis (AP) Potential to Transform How cUTI Patients are Treated NI, non-inferiority; NDA, new drug

application * The trial at 95% confidence interval (CI) achieved success (a -9.7 NI margin) within the original -10% NI margin One well-controlled pivotal trial to form the basis for an NDA submission as per FDA interactions New drug application

(NDA) accepted by the FDA, with Priority Review, PDUFA Date: June 27, 2022

All Oral Tebipenem HBr 685 patients

Pivotal Phase 3 Trial Design: Evaluation of Oral Tebipenem HBr compared to IV Ertapenem Randomization All IV Ertapenem 687 patients Primary Endpoint Head-to-Head Comparison: Oral vs. IV Oral Only Tebipenem HBr (600mg q8h) IV Only Ertapenem

(1g q24h) Duration of therapy 7-10 days Adult patients 18 years Innovative Trial Design Compares an Oral-Only Regimen Directly Against an IV Regimen for cUTI and Acute Pyelonephritis (AP) Showing active treatment arms only; study is

placebo-controlled double-blind, double-dummy Combined Clinical Cure and Microbiological Eradication Additional evaluation at LFU (23-27 days after first dose of study drug) Non-inferiority margin of -12.5% Masked individual and composite PK

data reviewed by an independent review committee after enrolling the first 70 patients to confirm dose Screening Overall Response rate at TOC in micro-ITT population (17-21 days after first dose of study drug) vs. cUTI, complicated urinary

tract infection; ITT, intent-to-treat; IV, intravenous; LFU, long-term follow-up; q24h, every 24 hours; TID, three times daily; TOC, test-of-cure

ADAPT-PO Met Its Primary Efficacy

Endpoint ADAPT-PO primary endpoint: Clinical cure + microbiological eradication at test-of-cure in micro-ITT population Tebipenem HBr Demonstrated Statistical Non-inferiority Compared to Ertapenem Demonstrated non-inferiority at margin

of -12.5%* Results were similar between treatment arms across all subgroups of patients * The trial at 95% confidence interval (CI) achieved success (a -9.7 NI margin) within the original -10% NI margin TBP-PI-HBr, tebipenem HBr; ERT, ertapenem

ADAPT-PO Key Secondary Endpoints

Evaluating Patient Outcomes Clinical cure rates at test-of cure (TOC) for micro-ITT groups comparable between the oral tebipenem HBr and IV ertapenem treatment arms Comparable Clinical Cure Rates at TOC Median duration of therapy was similar for

both treatment groups Micro ITT = Microbiological Intent-to-treat Durable clinical response observed with high clinical cure rates at TOC sustained through late follow-up visit Clinical cure rate is a key determinant in routine clinical management

ADAPT-PO Safety and Tolerability

Results Safety and tolerability profiles similar across the oral tebipenem HBr and IV ertapenem arms TEAE rates generally consistent with that of the carbapenem/beta-lactam class Diarrhea and headache were the most commonly reported TEAEs in

both treatment groups No C. difficile infections in tebipenem HBr arm No deaths reported SAE, serious adverse event; TEAE, treatment emergent adverse events; C.difficile, Clostridiodes difficile; ALT, alanine aminotransferase; AST, aspartate

aminotransferase Oral Tebipenem HBr IV Ertapenem Patients with at least one TEAE 25.7% 25.6% Diarrhea 5.7% 4.4% Headache 3.8% 3.8% ALT increase 1.0% 1.0% AST increase 1.0% 0.7% Serious TEAEs 1.3% 1.7% Drug-related SAEs 0.0% 0.3%

ADAPT-PO: Landmark Trial with

Potential to Change Clinical Practice Head-to-head results support regulatory submission of tebipenem HBr for the treatment of cUTI/AP Landmark trial demonstrating value of all oral regimen First all oral regimen for cUTI in 26 years, if approved

Non-inferior efficacy to IV ertapenem Met primary endpoint of combined clinical cure and microbiological response at TOC Safety results similar to IV ertapenem No drug related SAEs for tebipenem HBr; comparable GI TEAE rates

No branded or generic oral

substitutes in the carbapenem class Existing, large, and growing unmet need Primary reimbursement outside of the hospital Current practice and financial incentives support usage Prescriber base beyond infectious disease specialists Tebipenem HBr has

the Potential to be a Highly Differentiated Therapy if Approved

Lack of Oral Options for cUTI

is Widespread, Costly, and Addressable 2000-2004 Hospital Community $10,741 $7,083 76% Increase in hospitalizations +2 Days Longer Stays in Hospital Resistance + No Viable Oral cUTI Option = 2.3M Potentially Avoidable Hospitalizations Major

Unnecessary Cost Growing Fluoroquinolone Resistance 2000-2004 If approved, tebipenem HBr could help shift care back to outpatient setting: Helping patients to Go Home or Stay Home QuintilesIMS NDTI and MIDAS Database; Quintiles/IMS

Market Assessment 2017, Simmering, Jacob E. et al. "The Increase in Hospitalizations for Urinary Tract Infections and the Associated Costs in the United States, 1998-2011." Open Forum Infectious Diseases 4.1 (2017):

ofw281. PMC. Web. 15 Mar. 2018.; (Simmering et al. 2011). STEWARD 2019 Hospital resistance Data on file; BD 2019 community resistance data on file. Avoidable hospitalization estimates derived primarily from QuintilesIMS market assessment

(August 2017); *Resistance estimates directly from market assessment. cUTI= Complicated urinary tract infection 2019 2019

Tebipenem HBr Developed to Address a

Large and Existing UTI Population Stay Home: Hospital Avoidance Katrina, college student at the University of Kansas, experienced "a U.T.I. that did not respond to three different rounds of antibiotics." "It got so bad that I was

out of school for months and had to get a medical withdrawal," she said. Go Home: Get Home Sooner From Hospital "Timothy, a medical student, was hospitalized with E. coli that was highly resistant to a wide variety of antibiotics.

His discharge was delayed because the resistant nature of the bacteria would require insurance approval of home IV antibiotics." Sources: NYT Aug 20, 2019; IDSA Faces of Antimicrobial Resistance OPAT: Outpatient parenteral antimicrobial

therapy Treatment currently includes: Evaluation for systemic involvement requiring hospitalization Referral to urologist to evaluate structure abnormalities Cycling through available oral antibiotics to avoid hospital admittance Treatment currently

includes: Full course of IV antibiotics within the hospital OR Transition from hospital to outpatient IV antibiotic therapy and monitor for complications

Source: IQVIA NDS Database, Accessed

11/06/2018; AMR data on use by indication; 2017 UTI data projected Source: IQVIA NDS Database, accessed 11/06/2018 Ertapenem is the most used carbapenem to treat UTI Outpatient calculated as volume in "Clinics" and "Home Health and

Long Term Care" channels *Analysis excludes Meropenem - price, dosing regimen and stability data do not make it a widely used outpatient option 12% 115% *9M DOT x $350/day = $3 billion Carbapenem use in UTI and in outpatient setting has

increased significantly Carbapenem Market Estimated at $3B in United States Alone*

Large Market Opportunity for

Patients Able to Be Treated at Home Source: IQVIA 2019; Komodo 2020 data; Becton Dickinson Market Research, 2020 Pip/tazo = Piperacillin and tazobactam Targeted patients often cycle through multiple therapies Lack of effective oral

treatment options has resulted in increased Outpatient visits Emergency department visits Unwarranted outpatient IV use Unnecessary hospitalizations Hospital days Home Health and LTC stays post-hospitalization 5.2 M 1st line Oral 1.6 M 2nd

line Oral (Resistant/Failed) 1.1 M IV Therapy/3rd+ line Oral (Resistant/Failed) 7.9 M UTI Patients in the US Spero Focus 2.7M UTI prescriptions 2nd line + Oral or IV therapy 780 K IV Carbapenem Pip/tazo 1.9 M >2nd line Oral (Resistant/ Failed)

Targeted Launch Based on

Concentrated Prescribers and Focus on Urology Source:: IQVIA 2019; 1.35 = 50% of volume (deciles 6-10) from IQVIA 2019; Komodo 2020 data; Becton Dickinson Market Research, 2020 Pip/tazo = Piperacillin and tazobactam Initial sales team

focused on high volume retail practices and hospitals Spero will implement staged ~125 FTE field force by further segmenting for: Resistance (zip code level data) Favorable payer mix Adoption readiness, e.g. use of carbapenems Urologists: Largest

treaters for 2nd line UTI patients across retail and hospital outlets2 780 K IV Carbapenem Pip/tazo 1.9 M >2nd line Oral (Resistant/ Failed) 5.2 M 1st line Oral 1.6 M 2nd line Oral (Resistant/Failed) 1.1 M IV Therapy/3rd+ line Oral

(Resistant/Failed) 7.9 M UTI Patients in the US Spero Focus 50% patients in high-decile accounts Highly concentrated opportunity in both retail and hospital 2.7 M Spero Market

Unmet Need Identified by Healthcare

Providers; Expect Broad Access Across Payer Channels HCPs identify carbapenems as a preferred drug class for our target patients HCPs and payers see potential value of tebipenem HBr Interactions with 100+ Health Care Professionals and 150M Payer

Lives There is high agreement that relapsed, failed cUTI patients could be treated at home If approved, payers expect to broadly cover tebipenem HBr due to unmet need for new oral therapy "We need more drugs for UTI beyond Macrobid for lower

UTI, Keflex and Cipro. There is a lot of resistance to FQ, so if we want an oral, we need something new." - Urologist "Switching to PO would be far preferable to a PICC and Home Health or having them return to an infusion

center..." - KOL "We don't have any oral carbapenems now to send them home. This would shorten length of stay markedly and it covers ESBLs for hospital and community!" - Hospitalist "The value proposition here is