Third Dose of mRNA Vaccine Declines After 4 Months

The waning effectiveness of the third dose of mRNA COVID-19 vaccine has been studied.

Although protection decreased with time, a third dose was still highly effective at preventing severe illness with Covid-19.

"The mRNA vaccines, including the booster shot, are very effective, but effectiveness declines over time," said co-author Brian Dixon from the Indiana University.

‘Waning immunity was observed during both the Delta and Omicron variant waves in similar fashion to how mRNA vaccine effectiveness wanes after a second dose.’

"Our findings suggest that additional doses may be necessary to maintain protection against Covid-19, especially for high-risk populations."

Overall, the study reported that individuals with second and third doses of an mRNA vaccine had greater protection against hospitalisations (severe disease) than against emergency department/urgent care (ED/UC) visits (symptoms which may not require hospitalisation).

Vaccine effectiveness was also lower overall during the Omicron period than during the Delta period.

Vaccine effectiveness against ED/UC visits declined from 97 per cent within the first two months of receipt of a booster to 89 per cent effectiveness at four months or more during the Delta-predominant period (summer/early fall 2021).

During the Omicron-predominant period (late fall 2021/winter 2021-22), vaccine effectiveness against ED/UC visits was 87 per cent during the first two months after a third dose, decreasing to 66 per cent at four months after a third dose.

After the third dose, protection against Delta variant-associated hospitalisation declined from 96 per cent within two months to 76 per cent after four months or longer.

Vaccine effectiveness against Omicron variant-associated hospitalisations was 91 per cent during the first two months declining to 78 per cent at four months.

Source: IANS