The purpose of this study is to measure immunity to the flu vaccine over time in patients who had COVID-19. Adults who have been diagnosed with COVID-19 as well as controls without COVID-19 will be invited to participate in this study.

The primary aim of this study is to define the immune responses to the infant's initial influenza exposure (vaccine or infection) and how that affects the immune response to subsequent influenza exposures.

The purpose of this study is to use digital devices to collect data from participants in challenge studies that could indicate subtle changes in health during an infection that might otherwise go unnoticed.

This is a prospective, single-arm study designed to understand the mechanisms that lead to a loss of response to influenza vaccine in older adults.

The study design will be a longitudinal cohort study, which will allow for the determination of the time course of enhanced thrombin generation potential in relation to clinical outcomes and changes in markers of cellular activation in serial samples obtained from COVID-19 patients for up to 3 years after infection with SARS-CoV-2

The primary objective of this study is to assess the safety of two doses of DCVC H1 HA mRNA vaccine administered intramuscularly in healthy adults (18-49 yrs) at dosage levels of 10 mcg, 25 mcg, and 50 mcg.

Researchers at the National Institutes of Health (NIH) are recruiting for an inpatient flu study to learn more about flu. If you are healthy and interested in helping us fight the flu, we need you for this research study!

This is a dose-finding and pathogenicity study following human challenge with a low pathogenicity avian influenza A H10N7. Participants will be inoculated with 1 dose of challenge virus during the study and then followed for a minimum of 9 weeks after inoculation. Progressively increasing doses will be used according to a specific plan until either the maximum dose is reached or at least 60% of participants develop mild to moderate influenza disease (MMID).

The purpose of this study is to evaluate the immune response of the killed flu vaccine in healthy subjects.

In this study, the investigators will measure influenza virus cellular and humoral immune responses in individuals of different birth years before and after influenza vaccination.

The purpose of this study is to obtain samples from people with respiratory viruses to learn more about respiratory virus infections and the immune responses against them.