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Study: Hair Loss Following COVID-19 Vaccination

A study by Y. Zhu et al titled “Alopecia areata following COVID-19 vaccine: a systematic review” published on 5 July 2024 discusses hair loss after COVID-19 vaccination. Alopecia areata (AA) is an autoimmune condition that impacts the hair follicles, thereby causing hair loss.

The paper is 16 pages long, with a table summarizing the results spanning 9 pages.

The review screened hundreds of articles, narrowing down to 25 articles from around the world. This covered 51 patients. The sample is small but it does cover a decent age range.

In total, 51 patients, including 31 females (60.7%) and 20 (39.3%) males, were included. The average age of these patients was 37.6 years (37.6 ± 16.5 years). Seven patients (13.7%) were aged older than 60 years, four (7.8%) were aged younger than 20 years, and the remaining forty (78.5%) were aged between 20 and 60 years.

The onset of hair loss ranges from a few days after the first dose to even a few weeks after the second dose. A few weeks after the first dose is common.

Twenty-six of the 51 (50.9%) patients experienced hair loss within one month after the 1st dose, 13 of the 51 (25.5%) experienced hair loss within one month after the 2nd dose… In general, the incidence decreased gradually over time. Among the 51 patients, 34 patients (66.7%) experienced a patchy AA, while eight patients (15.6%) progressed to alopecia totalis (AT), and nine patients (17.7%) progressed to AU.

It should be noted that “27 patients (52.9%) developed new-onset AA following COVID-19 vaccination, while 24 patients (47.1%) presented with relapsed or aggravated AA”.

As for the causality assessment, 10 of 51 patients (19.6%) were classified as “consistent with causal association to immunization”, 14 of 51 patients (27.4%) were “indeterminate”, and 27 of 51 patients (53%) were classified as “coincidental association”.

The abovementioned 10 patients were all new cases.

It should also be noted that 23 (45.1%) of 51 patients received Pfizer although this could simply be due to its wider use. Of the abovementioned 10 patients, 4 received Pfizer.

Six patients (11.8%) had thyroid disease. None of these patients were part of the abovementioned 10 patients.

The incidence of thyroid disease has varied from 8 to 28% in patients with AA. Noso et al. have previously reported an association between thyroid autoimmunity and AA. In their study, they found a positive association of DRB1*15:01-DQB1*06:02 with AA in thyrotropin (TSH) receptor antibody-positive patients, indicating a common etiology and susceptibility between AA and autoimmune thyroiditis.

The exact mechanism is not clear but the researchers discuss their suspicions.

Vaccine-associated autoimmunity due to either cross-reactivity between antigens or the effect of adjuvants is a well-known phenomenon. mRNA vaccines such as Pfizer BNT162b2 can lead to the self-production of antigenic proteins that can stimulate the host immune response. As a result, proinflammatory cascades are activated, and numerous cytokines, including interferon (IFN) and interleukin (IL)-6, are released. IL-6 can inhibit the proliferation of hair follicle stem cells and keratinocytes and the transition of hair follicles from telogen to anagen. IFN can cause the collapse of immune privilege in human follicles. In addition, based on an adenoviral vector delivering the gene encoding the spike protein, the AZD1222/ChAdOx1 vaccine shares the same goal of evoking T cell-mediated immune reactions.

So, whilst the sample is small, there is a definite link between COVID-19 vaccination and AA, commonly within one month of receiving the first dose.


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