A study by Chile's Catholic University has shown that the Chinese-developed Sinovac anticoronavirus vaccine's effectiveness was down after six months and patients would then need a third dose of the immunizer.
Three out of four people who had received Sinovac had neutralizing antibodies six months after the full treatment but after that point, the defences against Covid-19 tend to disappear, particularly regarding the new variants.
Sinovac protection is at its peak two weeks after the second dose and 42 days after the first one, but from that point on the levels of antibodies begin to fall. After 180 days of the first dose (or 152 days of the second), the level of antibodies was seven times lower.
Nevertheless, Sinovac has proven to be 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 evade the ability to neutralize infection. So much so that for Delta - the variant which has spread the most in the world - the serum of those vaccinated is ten times weaker than with 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 throughout places such as Thailand. This research also verified that Sinovac provides 80-90% immunity for the Alpha variant but is far less effective against the Delta strain.
On the other hand, Chilean epidemiologist and paediatrician Mónica Pujadas explained that Coronavac was “a very good, 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 did it in a very mild way.
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.