Chinese COVID-19 vaccine maintains protection in variant-plagued Brazil - Science Magazine

Preliminary results from a large study of health care workers now suggest one dose of CoronaVac, a vaccine developed by a Chinese company, is still about 50% effective against symptomatic COVID-19 in a Brazilian city where more than three-fourths of new cases are caused by the highly transmissible variant known as P.1.

That real-world protection is about the same level clinical trials saw with two doses of CoronaVac against the standard, or “wild type,” pandemic coronavirus in the country, suggesting the variant’s mutations have not increased SARS-CoV-2’s ability to evade vaccine-evoked immune responses.

Although 50% effectiveness is far below the greater than 90% real-world protection of COVID-19 vaccines made with messenger RNA (mRNA), it may still be good enough to curb the disease’s spread within Brazil; vaccines with that level of efficacy in a clinical trial qualify for emergency use in many places and meet the World Health Organization’s threshold, as well.

Moreover, CoronaVac likely offers far greater protection against severe disease, hospitalization, and death than against milder cases of COVID-19.

That was seen in two dose efficacy trials conducted in Brazil and other countries and is typical of COVID-19 vaccines.

CoronaVac contains inactivated whole copies of SARS-CoV-2, in contrast to many other COVID-19 vaccines, including the mRNA vaccines, which just present the spike protein of the virus to the immune system.

The CoronaVac study involved medical data from 67,718 health care workers from Manaus, a city in the Amazon region that is the epicenter of the P.1 variant.

To estimate CoronaVac’s effectiveness, the researchers focused on 2656 health workers who had taken polymerase chain reaction (PCR) tests for SARS-CoV-2 infections beginning in January, with the initial rollout of the vaccine, through last week.

The 49.6% real-world effectiveness is similar to the vaccine’s efficacy of 50.34% against symptomatic COVID-19 after both doses, found in a phase 3 clinical trial conducted in Brazil by the Butantan Institute, a state-owned research institute and vaccinemaker.

On the other hand, Feigl-Ding says, measuring vaccine effectiveness in Brazil may produce artificially low results because there is a high risk that people have some immunity because of previous contact with the virus.

This could also explain why the CoronaVac clinical trial in Brazil showed lower efficacy numbers (50%) than in other countries such as Turkey (83.5%) and Indonesia (65%).

CoronaVac may prove better in a general population, as the new trial’s data come from health care workers who are highly exposed to the virus, points out immunopathologist Bruno Filardi at the Brazil Cancer Institute.

Croda and his colleagues will continue to analyze the effectiveness of various COVID-19 vaccines against P.1 and other variants with larger groups of people.