This spontaneous case was reported by a consumer and describes the occurrence of NEUTROPHIL COUNT DECREASED (Neutrophils have been at critically low levels/low blood count situation), INFLUENZA LIKE ILLNESS (Light flu like symptoms), FATIGUE (Fatigue) and INTERCHANGE OF VACCINE PRODUCTS (received the Janssen COVID-19 vaccine and then received two doses of the Moderna COVID-19 vaccine) in a 54-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 062E21A and 049E21A) for COVID-19 vaccination. Co-suspect product included non-company product VALACICLOVIR for Shingles.Previously administered products included for COVID-19 vaccination: Janssen covid 19 vaccine on 14-Mar-2021. Past adverse reactions to the above products included No adverse event with Janssen covid 19 vaccine.Concurrent medical conditions included Lymphoma (She was in remission and not took any treatments for the lymphoma.) and Shingles (Because she still has the infection, she has been on the antiviral treatment since May2021) since May 2021.Concomitant products included MULTIVITAMINS [VITAMINS NOS] and VITAMIN D [VITAMIN D NOS] for an unknown indication.  In May 2021, the patient VALACICLOVIR (unknown route) dosage was changed to at an unspecified dose.On 12-Aug-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form.On 09-Sep-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On an unknown date, the patient started VALACICLOVIR (unknown route) at an unspecified dose. In 2021, the patient experienced NEUTROPHIL COUNT DECREASED (Neutrophils have been at critically low levels/low blood count situation). On 09-Sep-2021, the patient experienced INTERCHANGE OF VACCINE PRODUCTS (received the Janssen COVID-19 vaccine and then received two doses of the Moderna COVID-19 vaccine). In September 2021, the patient experienced INFLUENZA LIKE ILLNESS (Light flu like symptoms) and FATIGUE (Fatigue). On 09-Sep-2021, INTERCHANGE OF VACCINE PRODUCTS (received the Janssen COVID-19 vaccine and then received two doses of the Moderna COVID-19 vaccine) had resolved. In September 2021, INFLUENZA LIKE ILLNESS (Light flu like symptoms) and FATIGUE (Fatigue) had resolved. At the time of the report, NEUTROPHIL COUNT DECREASED (Neutrophils have been at critically low levels/low blood count situation) had not resolved. DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available):In January 2021, Neutrophil count: normal (normal) Normal.In April 2021, Neutrophil count: normal (normal) Normal.In 2021, Neutrophil count: low (Low) critically low levels. For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.No treatment medications were reported.The patient received the Moderna vaccine in August and September 2021. Since that time, her neutrophils have been at critically low levels. The root cause of this drop in neutrophils (they were normal during routine checks in January and April of this year) was not established. The patient also had some fatigue and light flu-like symptoms after receiving both doses. Those symptoms lasted for approximately 24 hours, but she says it was nothing major. She reported that after receiving the second dose of the Moderna vaccine, her neutrophil count had been very low. She mentioned that she has a history of chronic lymphoma for which she has been treated in the past. She was currently in remission and was not going through any treatments for the lymphoma. She sees an Oncologist and Hematologist for regular checkups. She was diagnosed with Shingles in May 2021 for which she was put on Valcyclovir. Because she still has the infection, she has been on the antiviral treatment since  May 2021. She stopped taking the shingles treatment to see if it would make a difference in her neutrophil count, but nothing happened for 2 weeks after stopping the medication and her neutrophil count was still low. She then decided to restart the Valcyclovir treatment. She was trying to figure out the reason for the low neutrophil count and wants to know if there is any data which points to the Moderna vaccine as the cause.This case was linked to MOD-2021-422103 (Patient Link).Most recent FOLLOW-UP information incorporated above includes:On 20-Dec-2021: Non-significant Follow up information received: I narrative updated.On 21-Dec-2021: Significant Follow up received: Events (fatigue and light flu like symptoms), medical history (Shingles and lymphoma), historical vaccine, Co-suspect and concomitant medications added. I narrative updated.; Sender's Comments: This case concerns a 54-year-old female patient with medical history of chronic lymphoma (currently in remission, as stated). After administration of the second dose of the mRNA-1273 vaccine, the patient experienced non-serious unexpected events of Neutrophil count decreased and Influenza like illness, as well as non-serious expected event of Fatigue. The events of Fatigue and Influenza like illness lasted only 24 hours and then resolved without any treatment. However, the patient developed very low neutrophil count after this second dose that was still ongoing at the time of this report (laboratory findings with reference ranges were not provided). Co-suspect medication Valaciclovir which was used for the treatment of Herpes zoster infection remains a significant confounding factor for this event. In addition, underlying lymphoma is considered as an additional significant confounding factor for this event. The re-challenge for the events of Fatigue and Influenza like illness could have been considered positive, having in mind that it was confirmed that the patient developed these events after the first dose, as well. The benefit-risk relationship of the mRNA-1273 vaccine is not affected by this report. Event seriousness assessed as per Regulatory Authority reporting. Having in mind that this patient received the Janssen COVID-19 vaccine prior to vaccination with the company product, Interchange of vaccine products should have been considered in this specific case. The company causality for this event is not applicable.