if half, or two-thirds, or whatever it is, of the immune response is not going to be effective, and you're left with the residual half, then the more boosted that is the better." professor francois balloux of the genetics institute at university college london said, "from what we have learned so far, we can be fairly confident that – compared with other variants – omicron tends to be better able to reinfect people who have been previously infected and received some protection against covid-19. that is pretty clear and was anticipated from the mutational changes we have pinpointed in its protein structure. these make it more difficult for antibodies to neutralise the virus." ba.1 and ba.2 a january 2022 study by the uk health security agency found that vaccines afforded similar levels of protection against symptomatic disease by ba.1 and ba.2, and in both it was considerably higher after two doses and a booster than two doses without booster, though because of the gradually waning effect of vaccines, further booster vaccination may later be necessary. ba.4 and ba.5 in may 2022, a preprint indicated omicron subvariants ba.4 and ba.5 could cause a large share of covid-19 reinfections, beyond the increase of reinfections caused by the omicron lineage, even for people who were infected by omicron ba.1 due to increases in immune evasion, especially for the unvaccinated. however, the observed escape of ba.4 and ba.5 from immunity by a ba.1 infection is more moderate than of ba.1 against studied prior cases of immunity (such as immunity from specific vaccines). immunity from an omicron infection for unvaccinated and previously uninfected was found to be weak "against non-omicron variants", albeit at the time omicron is, by a large margin, the dominant variant in sequenced human cases. bq.1 and bq.1.1 subvariants bq.1 and bq.1.1 were found in late 2022 to be better at escaping first and booster vaccines than previous variants, and "to have pretty much eliminated every single monoclonal antibody on the market right now in terms of their efficacy". vaccine adjustments