Thread by @joshmich

Keeping a wary eye on Covid trends in South America. The good: cases/deaths there have come down from devastating peaks a few months back, and there’s progress on vaccinations. The bad: Delta may have only begun to circulate, and questions about vaccine efficacy

Most countries in the region have fully vaccinated between 20 and 40% of their populations; Chile and Uruguay stand out, with >70% fully vaccinated. Countries use a mix of vaccines, mostly Chinese inactivated vaccines (Sinovac and Sinopharm), plus some Pfizer & AstraZeneca

Chinese vaccines have lower effectiveness vs symptomatic disease but protect vs hospitalizations and death.
Chile estimated the Sinovac VE vs. symptomatic Covid at 58%, and 86% vs hospitalization. For Pfizer: 88% and 97%, AZ: 68% and 100%, respectively
minsal.cl/wp-content/upl…

Genomic sequencing data is fairly limited, but appears Gamma, Beta, Lambda have been responsible for much of the disease transmission in the region this year. Still, some signs Delta may be nosing its way in.

Data from covariants.org shows the proportions of different variants sequenced in countries over time. The Delta proportion (in green) has expanded quickly in Brazil & Argentina, and less common but increasing in Chile and Ecuador (again, limited data).

In almost every place Delta has taken root it has come to dominate transmission, due to its innate advantage of higher transmissibility. Could South America be looking at a Delta surge in the next weeks/months?

Also, will the effectiveness of Chinese vaccines, which make up the bulk of many countries’ vaccinations in the region, be compromised further because of Delta?

Data on these vaccines vs Delta hard to come by but a new *pre-print* raises concerns.
researchsquare.com/article/rs-828…

Authors reviewed outcomes in vaccinated vs unvaccinated, comparing across different vaccines in Bahrain, finding "a higher risk of COVID-19 infection and clinical escalation among recipients of the Sinopharm vaccine compared to other vaccine recipients” (especially in those >50)

So, a concern in South America that Delta spread creates another surge, and many people could be still be vulnerable despite fairly high vaccination coverage. For this reason, some governments have already moved to 3rd dose boosters for those who received Chinese vaccines.

Uruguay, for example, is asking that everyone in the country who received 2 doses of Sinovac receive a 3rd dose (of Pfizer). Chile has also started with booster shots for Sinovac recipients.
gub.uy/ministerio-sal…

Still, not all countries in the region are ready and able to provide 3rd doses, and are still struggling to get increase vaccine coverage for the first two doses.

Will be continuing to watch the situation