COVID-19 Vaccine Found to Be Effective against Brazilian P.1 Variant

The inactivated vaccine, CoronaVac, proved effective in combatting COVID-19 in the city of Manaus, Brazil, where the highly transmissible P.1 variant emerged and has devastated the local population, researchers from Brazil and the Yale School of Public Health have found.

CoronaVac was shown to be 50% effective in preventing illness 14 days after administration of the first dose in its two-dose schedule. The study was conducted among nearly 70,000 health care workers in Manaus, which was the epicenter for the emergence of the P.1 variant.

It is the first study to evaluate the effectiveness of a COVID-19 vaccine in places where P.1, often referred to as the “Brazilian variant,” is widespread. Data will continue to be collected over the next few weeks to determine CoronaVac’s effectiveness after the second dose.

The findings are published on the pre-print server MedRxiv and have been submitted for scientific peer review and publication.

“The majority of people in the study had only received their first vaccine dose. Overall effectiveness may turn out to be higher as more people receive their second dose,” said lead investigator, Julio Croda, a senior researcher at the Oswaldo Cruz Foundation, Brazilian Ministry of Health, and adjunct professor at the Yale School of Public Health. “This is a critically important finding for it tells us that ramping up vaccination will turn the tide against the devastating resurgence we are experiencing in Brazil due to the spread of the P.1 variant.”

Brazil has been particularly hard hit by the pandemic and variants of the virus. The overall death toll from COVID-19 is close to 337,000 (second only to the United States) and Brazil recently recorded more than 4,000 deaths in a single day. In many cities, the health care system has collapsed and been unable to care for people who are sick and dying.

The P.1 variant was first identified in Manaus in December 2020 and has rapidly spread throughout Brazil and globally, including the United States. The variant has a variety of mutations that make it more transmissible and potentially able to escape the immune response. In recognition of this threat, the World Health Organization has declared P.1 a “variant of concern.”

“This variant has not only created a public health emergency in Brazil but is a threat to other countries in South America and beyond,” said Albert Ko, a professor at the Yale School of Public Health who works extensively in Brazil and a co-author of the study. “National leaders and the global community need to secure the needed vaccine supply and deploy them as quickly as possible, in addition to implementing sound public health prevention, to preempt the impending humanitarian crisis.”

In addition to studying health workers from Manaus, Croda said that the VEBRA-COVID consortium will evaluate the effectiveness of CoronaVac and AstraZeneca/Oxford vaccine in the city’s general population as well as in other Brazilian cities, Campo Grande and São Paulo. The VEBRA-COVID consortium includes researchers from Brazil and international partners, which include the Pan-American Health Organization, University of Florida, and Stanford University.