Lymph nodes are small, bean-shaped structures that function as filtering stations and command centers for the immune system. They are distributed throughout the body, containing specialized white blood cells that identify and neutralize foreign invaders like viruses. When the body encounters the SARS-CoV-2 virus, or a component of it, these nodes can become noticeably enlarged and tender, a response known as lymphadenopathy. This swelling is a physical manifestation that your immune system is actively engaged in defense. Understanding this reaction helps to clarify why this symptom may occur with COVID-19.
Lymph Node Swelling Caused by COVID-19 Infection
The swelling of lymph nodes during a COVID-19 infection signals an active immune response. When the SARS-CoV-2 virus enters the body, its antigens are transported via the lymphatic fluid to nearby lymph nodes. Within these nodes, a rapid proliferation of immune cells, primarily B-cells and T-cells, begins. This process, called germinal center formation, is how the body prepares to neutralize the threat.
The resulting increase in the number and size of these immune cells physically inflates the node, causing the tenderness and palpable lump. The virus itself may also directly infect the lymph nodes, as the ACE-2 receptors it uses to enter cells are present in lymphatic tissue. This direct viral presence further stimulates the local inflammatory response. This type of swelling is a reactive benign condition, reflecting the body’s successful recognition and processing of the viral threat.
Understanding Post-Vaccination Lymphadenopathy
Swollen lymph nodes are a common side effect following COVID-19 vaccination, particularly with the messenger RNA (mRNA) vaccines. The mechanism is similar to infection but is triggered by the vaccine’s contents rather than the live virus. The mRNA vaccines instruct cells near the injection site to temporarily produce the SARS-CoV-2 spike protein.
The local lymph nodes collect these spike proteins and the surrounding inflammatory signals, initiating an immune response. This leads to the same rapid expansion of B-cells and T-cells seen during natural infection. This side effect is a sign of a robust immune response building protective antibodies and memory cells against future exposure. The lymphadenopathy confirms the vaccine is working as intended.
Common Locations and Typical Duration
The location of lymph node swelling provides a clue about the source of the immune activation. For an active COVID-19 infection, which primarily affects the respiratory system, the swelling most commonly occurs in the cervical nodes in the neck or the submandibular nodes under the jaw. These regions drain the throat and upper respiratory passages where the virus often establishes itself. This swelling typically begins a few days after the onset of infection and may persist for several weeks as the body clears the virus.
In contrast, post-vaccination lymphadenopathy is almost always localized to the axillary region, or the armpit, on the same side as the intramuscular injection. The lymph nodes in this area are the first checkpoint for the vaccine components delivered to the shoulder muscle. The swelling usually appears two to four days after vaccination. While it often resolves within one to two weeks, the enlargement can sometimes be visible for up to several months.
Warning Signs and When to Consult a Doctor
While most COVID-19-related lymphadenopathy is temporary, certain characteristics warrant a medical consultation. If the swollen lymph nodes persist for longer than two to four weeks after infection or after vaccination, a doctor should evaluate them. Nodes that are very hard, feel fixed or immobile beneath the skin, or are rapidly increasing in size require prompt medical attention.
Consult a healthcare provider if the swelling is accompanied by other concerning systemic symptoms. These may include an unexplained fever, night sweats, or significant, unintentional weight loss. Although lymphadenopathy is a common immune response, a medical evaluation can rule out other, more serious conditions that may also present with similar swelling.