The Food and Drug Administration announced a change to the fact sheet on Johnson & Johnson's COVID-19 vaccine Monday, warning of an increased risk of Guillain-Barré syndrome, a neurological disorder that damages the nerves and can lead to paralysis.

"Based on an analysis of Vaccine Adverse Event Reporting (VAERS) data, there have been 100 preliminary reports following vaccination with the Janssen vaccine after approximately 12.5 million doses administered," an FDA spokesperson said in a statement to CNET. Ninety-five of the cases were serious and required hospitalization, with one reported death, according to the FDA.

The cases of Guillain-Barré usually occurred about two weeks after vaccination and were typically found in males aged 50 and older, according to a statement by the Centers for Disease Control and Prevention. The CDC said it will discuss the link between the US's only single-dose COVID vaccine and the autoimmune disorder at an upcoming meeting of the Advisory Committee on Immunization Practices. It also said that most people fully recover from Guillain-Barré syndrome.

The known benefits of Johnson & Johnson's COVID-19 vaccine continue to outweigh the known risks, the FDA said. But those who got a Johnson & Johnson shot should seek medical attention if they develop the following symptoms, per the FDA: weakness or tingling sensations, especially in the legs or arms, that's worsening and spreading to other parts of the body; difficulty walking; difficulty with facial movements, including speaking, chewing or swallowing; double vision or inability to move eyes; or difficulty with bladder control or bowel function.

Combining vaccines

Four studies (not yet peer reviewed) posted this week show that a first dose of the AstraZeneca vaccine followed by a second dose of the Pfizer vaccine is well tolerated and induces potent humoral and cellular responses. Three of the studies (one from Spain, and two from Germany) did not include a comparison group vaccinated with two doses of AstraZeneca, but a fourth small study (also in Germany) did. This study showed that heterologous vaccination led to a significant 11.5-fold increase in anti-Spike IgG, as compared to the 2.9-fold increase after homologous AZ/AZ vaccination. It also induced significantly higher frequencies of Spike-specific CD4 and CD8 T cells and, in particular, higher titers of neutralizing antibodies against the B.1.351 (beta) and the P.1 (gamma) variants of concern.