Low immunity after Covid vaccination in some people worries experts

Thiravat Hemachudha, director of the Health Science Centre of Emerging Diseases at Chulalongkorn University, revealed that many people who had received two doses of the Sinovac vaccine for three to four weeks showed no neutralising antibody, or at only 20-30 per cent.

For a vaccine to be effective, the ability to inhibit a virus must be more than 20 per cent to develop immunity.

People who are normally vaccinated will have high, mid and low response, but they have to go up. Inactivated vaccines, such as the rabies vaccine, require three injections on day zero, three and seven and begin to see immunity in the blood around day 10 and develop in all people on day 14. Two injections a month apart are assessed at three or four weeks after the second dose. However, there should be a satisfactory level of growth in everyone, he said.

But, in some groups that were vaccinated on the same day and got the same vaccine, it appears that there was no immunity at all (less than 20 per cent). It is possible that the same lot of vaccines may have been a problem. Some have major congenital conditions, including diabetes that does not enhance the immune system, he said.

Some patients with Covid-19, who have been infected despite having had two doses of Sinovac or one dose of AstraZeneca, were still infected even in the post-injection immunity test, but it was not very high.

In cases where immunity does not increase, or is less than 68 per cent, which is a theoretical number correlated with virus prevention, they may want to consider getting a third dose of vaccine, either the same brand or a new one.

In the case of allergic reactions or side-effects, there is no clear evidence that it increases immunity because it is inflammation through different systems.

The number of vaccinations against Covid-19 in Thailand from February 28 to June 11 totalled 5,975,070 doses -- 4,362,685 first dose and 1,612,385 second dose.