Siriraj Hospital has found that both the AstraZeneca and Sinovac Covid-19 vaccines stimulate the same antibody levels as those found in former Covid-19 patients.
A study on the immune response and safety of Covid-19 vaccines found that 3-4 weeks after receiving their first dose of the AstraZeneca vaccine, volunteers had antibody levels similar to those who had recovered from the virus.
Conducted on Siriraj Hospital's vaccinated medical workers by the Siriraj Institute of Clinical Research, the study showed that 75% of those who had received the first dose of the Sinovac vaccine and 100% of those who had received both jabs had the same antibody levels as the recovered patients.
Some 75% of the volunteers experienced common side effects, including body aches, fatigue, fever and headaches, but these disappeared without treatment.
Recipients of the AstraZeneca vaccine had more symptoms than the Sinovac recipients, particularly those under 30. However, a single AstraZeneca jab and both shots of the Sinovac vaccine created similar immunity as former Covid-19 patients, leading researchers to conclude that both vaccines were effective against the disease.
The Siriraj Institute of Clinical Research is conducting a further study on the vaccines' efficacy against Covid-19 variants, such as those that originated in the UK, South Africa and India.
Chalermchai Boonyaleepun, deputy chairman of the Senate's public health committee, said studies by Siriraj Hospital and King Chulalongkorn Memorial Hospital had found that two doses of the Sinovac vaccine and one dose of the AstraZeneca vaccine created immunity as high as in people who had recovered from the disease.
Other studies by the hospitals found the first shot of the Sinovac vaccine raised patients' antibody level to 140 units but that soared to 1,691 units after the second dose, while the AstraZeneca vaccine fared far better, its first jab creating an antibody level of 997.7.
Nevertheless, every patient who received two Sinovac jabs had the same antibody levels as former Covid-19 patients. Institutions around the world say there is evidence that both vaccine-induced and natural immunity will last 6-9 months.
The government earlier this week decided the second dose of AstraZeneca vaccines would now be administered 16 weeks after the first dose, as opposed to 10 weeks but it insisted the delay would not have any negative effect on patients' immunity levels.
