COVID-19 Vaccines: EMA on AstraZeneca & Blood Clots / Variants / April 19

By Kelly Young

Edited by Susan Sadoughi, MD, and Richard Saitz, MD, MPH, FACP, DFASAM

Here are some of the latest developments on COVID-19 vaccines:

EMA on AstraZeneca vaccine & blood clots: The occurrence of thrombosis with thrombocytopenia should be considered a very rare side effect of the AstraZeneca COVID-19 vaccine, according to the European Medicines Agency. The World Health Organization said a causal relationship is "plausible but is not confirmed." Specifically, the EMA has received reports of 62 cases of cerebral venous sinus thrombosis and 24 cases of splanchnic vein thrombosis out of 25 million vaccine recipients. Eighteen cases were fatal. Most cases occurred in women under age 60 and within 2 weeks of receiving the first dose. Officials said that thrombosis with thrombocytopenia could be an immune response, similar to what is sometimes seen with heparin. The EMA said that the benefits of the vaccine outweigh the potential risks. Patients who receive the vaccine should seek medical attention if they experience shortness of breath, chest pain, swelling in the leg, persistent abdominal pain, neurological symptoms, and tiny blood spots under the skin.

Variants: Several letters to the New England Journal of Medicine highlight work on variants of the virus.

• In the first, among those who've already had COVID-19, a single dose of the Pfizer-BioNTech vaccine substantially increased neutralizing activity against several circulating variants. Researchers used 18 serum samples from six healthcare workers previously infected with the original virus. In the weeks after infection and again right before vaccination, neutralizing activity was shown against the original virus and the B.1.1.7 (first seen in the U.K.) and P.1 (first seen in Brazil) variants, but not the B.1.351 (first seen in South Africa) variant. Within weeks of vaccination, neutralizing antibody titers were 81-228 times as high as before vaccination, with significant improvement in all strains.

• In the second study, plasma collected from patients infected with the B.1.351 strain appears to elicit a strong antibody response against several other strains. Researchers studied roughly 90 hospitalized COVID-19 patients in Cape Town, South Africa. All were infected with the B.1.351 strain. Plasma from these patients maintained neutralization against both the original virus and against the P.1 variant (first observed in Brazil). The authors conclude: "Our data indicate that vaccines built on the spike protein of 501Y.V2 [also known as B.1.351] may be promising candidates for the elicitation of cross-reactive neutralizing antibody responses to SARS-CoV-2."

• The third study suggests that some existing vaccines may be less effective against the B.1.351 strain. Researchers studied serum from 49 Novavax and Moderna vaccine recipients. Relative to the original strain, B.1.429 (first identified in California) was 2-3 times less sensitive to neutralization by convalescent serum and by serum samples from vaccinated people, while B.1.351 was 9-14 times less sensitive. The authors say that "vaccine-elicited neutralizing antibodies are likely to remain effective against the B.1.429 variant. The magnitude of resistance seen with the B.1.351 variant is of greater concern with respect to current vaccines."

April 19: On Tuesday, President Joe Biden announced that as of April 19, all adults in the U.S. would be eligible for vaccination.