3rd COVID vaccine dose produces antibody against all variants

The level of antibodies was high both one and two months after vaccination in working-age people who received a third dose of the vaccine as a booster dose, according to a new study by Finnish Institute for Health and Welfare (THL).

Antibodies were found against all viral variants studied, i.e., delta, beta, and omicron variants, said the THL in a press release on Thursday referring to the study.

The THL study evaluated immune responses to the third vaccine dose in twenty adults aged 27 to 63 years and in nine nursing home residents aged 71 to 89 years.

Both Moderna´s Spikevax and BioNTech Pfizer's Comirnaty were studied.

Subjects had received the third dose of vaccine 6-9 months after the second dose. Antibodies were measured from samples taken 1-2 months after the booster dose.

In the elderly, the level of antibodies was, on average, lower than in the younger subjects, and was not sufficient in all subjects to neutralize the omicron and beta variants in laboratory experiments.

“The booster vaccine has been shown in previous studies to produce a 2 to 7 fold increase in antibody response compared to a second dose. The strength of the response is affected by the age of the vaccinees, the vaccine preparation, the interval between vaccine doses, and the methods used to measure the antibodies, ”said THL research manager Merit Melin.

Spikevax produces a strong immune response and is a recommended booster vaccine, especially for the elderly

A small proportion of the working age subjects had received a booster dose of Spikevax and had higher levels of antibodies than those who had received Comirnaty.

Spikevax has previously been shown to produce more than twice the level of antibodies compared with Comirnaty in adults receiving two doses of vaccine. The antibody concentration was the higher the younger the subjects.

Similarly, the efficacy of vaccines against infections and severe disease caused by alpha- and deltavariants has been found to remain somewhat better with two doses of Spikevax compared with those vaccinated with Comirnaty.

"Spikevax should be used for third doses, especially in the elderly, as it appears to produce a stronger immune response," said, THL chief physician Hanna Nohynek.

Antibody levels following the booster vaccine have been reported previously in an English study published in December . The study compared immune responses after booster vaccination with seven different covid-19 vaccines, of which the mRNA vaccines produced the strongest antibody response.

The omicron variant is able to evade antibody-mediated protection against infection, as not all antibodies produced by vaccination recognize the structures of the altered spike protein.

“Previous studies have shown that the level of antibodies induced by two doses of the vaccine is not high enough to effectively neutralize the omicron variant, although those vaccinated at the extended dose interval may be in a slightly better position,” said Melin.

The third dose of the vaccine raises the level of antibodies to a higher level, which is also sufficient to neutralize the omicron variant. The duration of protection against infection depends on how long the antibodies remain at a sufficiently high level.

"These results emphasize the importance of the third dose of vaccination now that we aim to slow down the spread of the omicron variant in Finland also by vaccinations," said Nohynek.