Ho Ching: Don’t presume a prior non-Omicron or a prior Omicron infection can prevent reinfection



Don’t presume prior non-Omicron infection or a prior Omicron infection can protect against reinfection.

One reported case in Denmark was reinfected in 20 days, albeit it is not clear if this is BA.1 vs BA.2. But it does indicate that there could be poorer cross protection even among the Omicron variants.

Protection of vaccines against long covid has drastically reduced to about 15% for Omicron.

So recovered patients should not presume they are safe from reinfection.

Studies are suggesting that BA.4 or BA.5 does not have any boosting effects, compared to a vaccine booster shot. This is due to the immune imprinting effect that is not yet fully understood.

So boost if you are due and not presume an Omicron infection would protect against a reinfection by Omicron.

The studies in UK, USA, and Europe are confounded by the high exposure to covid infections before the availability of vaccines. Antibody studies in UK schools showed that 99% had been exposed to prior infections, for instance.

So the immune imprinting in these areas would have folks esp in their healthcare system and schools already imprinted by the first waves of Wuhan, Alpha and other variant waves before the arrival of the vaccines.

The immune imprinting may be different for places which did not experience wild waves of non-Omicron, and were largely already vaccinated before they met the Omicron wave. These places include Sg, NZ. Australia, Taiwan, HK, China, Korea and Japan.

Others like North Korea now face the BA.5 without even vaccination in place.

So the immune imprinting studies should include multi-nation studies to cover the range of immune imprinting combinations.

Immune imprinting could make the immune system more complacent when meeting the same or new variant virus again. But immune imprinting could also enable the immune response to be more alert and responsive.

If the imprinting from a prior infection makes the immune more complacent, then we would not mount a strong defence early, and so may get more sick.

Something for parents and young people to watch too.

Omicron, particularly BA.5, seems to be more debilitating for infants, kids, teens and young adults, compared to the much milder infections for non-Omicron infections.

Parents and young adults should watch for persistent high fever that lasts for more than 2 days. Go see a doctor urgently if fevers are 40C or higher, and if fevers persist more than 2 days, esp for infants and young kids.

Reports are also pointing to the likelihood that the BA4 and BA.5 are both like the Delta in terms of sticking better to the lung cells. This could mean higher risk of lung damage or acute illness.

So do get your oximeter ready and track oxygen levels if you test ART+ for this current wave.


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