The Pfizer COVID-19 vaccine's efficacy falls to 47 percent after 5 months of taking the second dose, shows a large scale study published in the journal Lancet on Monday, 4 October.

It is according to the data from this study by Pfizer that the US health authorities took the call to allow booster shots of the vaccine, reported Reuters.

It must also be noted that the same study has found that the vaccine's effectiveness in preventing hospitalisation and deaths after the second dose remains high at 90 percent for the same period of 6 months.

This was noticed in the case of all the variants including Delta.

Could this study be another rung in the ladder towards allowing booster shots for all?

FIT breaks down the findings of the study.

The results of this particular study were released back in August for peer review.

Slightly over half the participants were female while 47.6 percent of them were male.

Here's a quick look at what the study analysis found.

• Effectiveness against overall infections dropped to nearly half, going from 88 percent during the first month after full vaccination, to 47 percent after 5 months.

• In the case of the Delta variant, the vaccine's effectiveness went from 93 percent in the first month to 53 percent after 4 months.

• Effectiveness against other (non-delta) variants was 97 percent in the first month after full vaccination and dropped to 67 percent at 4 to 5 months.

• The vaccine's overall protection against hospitalisation and death remained 90 percent.

• Protection against hospitalisation and death in the case of the delta variant also remained high at 93 percent.

According to the study researchers the cause for the drop in efficacy is because of the protection of the vaccine waning rather than due to certain variants being more contagious.

"To us, that suggests Delta is not an escape variant that is completely evading vaccine protection," study leader Sara Tartof with Kaiser Permanente Southern California's Department of Research & Evaluation, was quoted as saying by Reuters.

Pfizer has been pushing for the approval of booster shots of its COVID-19 vaccines for the general population on the grounds that the effect of the vaccine wanes over time.

So far, the US FDA has allowed boosters for those over the age of 65 and people who are immunocompromised. Health authorites, including the US CDC and the FDA have so far been reluctant to allow boosters for all citing a lack of data to suggest it is required for the general population.

(written with inputs from Reuters.)