RIO DE JANEIRO, BRAZIL – A study by Chile’s Catholic University has shown that the Chinese-developed Coronavac vaccine’s effectiveness declines after six months, so patients may need a third dose of the immunizer.
Three out of four people who had received the vaccine still had neutralizing antibodies six months after the full treatment; however, after that point, the defenses against Covid-19 tend to disappear, particularly regarding new variants.
Coronavac protection is at its peak two weeks after the second dose and 42 days after the first one, but the levels of antibodies begin to fall from that point on. After 180 days of the first dose (or 152 days of the second), the level of antibodies was seven times lower.
Nevertheless, the product has proven effective against any of the virus mutations found so far in Uruguay. But preliminary data for “variants of concern” (such as Alpha, Delta, or P1) indicate that, to varying degrees, they exhaust the ability to neutralize infection.
So much so that for Delta – the variant that has spread the most globally – the serum of those vaccinated is ten times weaker than against the original strain.
The Chilean investigation seems to agree with a joint study between the head of the Thai Red Cross Emerging Infectious Diseases Health Science Centre and a virologist at BIOTEC, which showed that Sinovac’s effectiveness against the Delta variant is particularly weak compared to that of the Astra-Zeneca vaccine.
The Delta strain is much more contagious and is spreading rapidly through places such as Thailand. This research also verified that Coronavac provides 80-90% immunity for the Alpha variant but is far less effective against the Delta strain.
On the other hand, Chilean epidemiologist and pediatrician Mónica Pujadas explained that Coronavac was “a perfect, safe and effective vaccine,” with less than 2% of the nearly 2,300 volunteers with two doses having had symptomatic Covid-19, and 94% of them only had “very mild” symptoms.
The Thai study revealed that mRNA vaccines are the most effective in battling the Delta variant of Covid-19. Without mRNA vaccines, the next best protection is 2 doses of the AstraZeneca drug, which has been proven in the study to have over 90% neutralizing antibody levels to combat the Delta variant.
Thai citizens who have received two doses of Sinovac are now advised to take a booster shot of AZ. It is not as effective as full AstraZeneca vaccination, but it is recommended for frontline medical personnel.