The COVID vaccinations have been deployed widely to help prevent complications from COVID infection. The vaccines reduce severity of illness such that hospitalization and death are less likely in people who have been vaccinated. In recent months, allergists have found ourselves at the intersection of the vaccination effort and potential complications of the COVID vaccines. When the vaccinations were first released, we fielded many questions regarding whether the vaccines were safe for people with allergies, and I wrote a blog detailing that most people with allergies can safely receive the COVID vaccines. In recent months, we have seen a rise in a new side effect of the vaccines: hives.
Hives can have many different causes and can even be unexplained where no cause is identified. We have seen a variety of rashes related to COVID illness and some of those same rashes can appear when people are vaccinated. In the last several months, mostly as more people receive booster vaccinations, we have seen an increase in hives. The hives tend to appear 10-14 days after the vaccination. There may also be dermatographism, which is a form of physical hives where raised lines develop when the skin is touched. The hives come and go and leave behind normal skin. May people will wonder whether the cause of their hives is food or medication allergy, but recently it has not typically been either.
Most patients with hives after the booster experience very intense symptoms at first, and then the hives slowly start to improve. For most patients, the hives will last less than 6 weeks. The best treatment for hives of any kind is usually higher doses of antihistamines. If the hives continue beyond 6 weeks, allergists may treat with Xolair, an injectable medication FDA approved for chronic hives. Your friendly neighborhood allergist can help tailor the dose of medications that will control your symptoms so you can get back to living your life.
The mechanism by which the COVID vaccines cause hives is not yet understood. We suspect that the hives develop as a side effect of the immune mechanism of the vaccine. The timing of the hives after the vaccines is not consistent with allergic reaction. Most allergic reactions happen within 2 hours of vaccination and the hives that are a side effect of the vaccines begin up to two weeks after vaccination. Interestingly, hives are not a typical side effect of most vaccines, though all vaccines affect the immune system and help recipients generate antibodies against viruses or bacteria. Many people who experience hives after the booster did not have any rash or hives after their first two vaccines. Anecdotally, we are seeing more hives after the mRNA boosters, but we don’t have aggregate data yet regarding which vaccines are more likely to cause hives. Swelling, or angioedema, is commonly associated with hives in general, but we haven’t seen angioedema after the vaccines as much as we have seen hives. I discuss potential future COVID vaccines with my patients, including whether the hives could recur in the future.
The community of board-certified allergists is talking amongst ourselves about the hives after the booster vaccines as many of us are seeing this phenomenon. We are hopeful we’ll have more concrete information about the rate of hives after booster in the next few months.