I received my booster vaccination at lunchtime today (Wednesday, January 12). My first two doses of Covid-19 vaccine were the virus-mediated version from AstraZeneca, with the second of these having been stuck into my arm in early September 20211.
Today I was speared in the same arm with the Pfizer vaccine, which is a messenger RNA (mRNA) type. This time, I hardly felt the needle, presumably because it was finer than those used for my two AstraZeneca doses.
When I received the AstraZeneca doses, I was given to believe that maxiumum protection would kick in at about two weeks after I received the second dose. Relying on the AstraZeneca vaccine for protection against the Omicron variant of the virus causing Covid-19 was a worry when it was rumoured that the protection was limited. This rumour turned out to be true.
In late December, 2021, a study from the UK suggested that protective effectiveness against symptomatic COVID-19 disease from the Omicron strain was not observable (i.e. it was nil) after two doses of the AstraZeneca vaccine and was only approximately 35% at about 4 to 6 months after two doses of the Pfizer vaccine. In addition, the study also looked at the effectiveness of booster doses. Although the sample number was small (10 cases receiving a booster after primary AstraZeneca vaccination and 16 cases after primary Pfizer vaccination), the protective effectiveness against symptomatic disease was estimated at about 70–75% after receiving a Pfizer booster dose for both groups2.
After receiving a booster such as that from Pfizer, positive effects begin after about a week. However, it takes about two weeks for the maximum protection level to be reached3. So, I should be as protected as I can be before the end of January. This is a bit of a relief, given that the Omicron walls seem to be closing in: a friend of mine has just tested positive; a colleague and all his family have just tested positive; the day-care centres for two of my grandchildren have had positive cases, so the kids have to stay at home and get tested, as do their parents; and there have been several positive cases (including one resident) at the nursing home where an elderly relative resides.