My incredible two-and-a-half-year run of negative COVID tests came to a halt last week, after receiving a text confirming that I was also in the latest catch of the pandemic. My case adds to the growing tide of the third omicron wave in seven months, currently rolling across Australia.
While shivering through my mild bout, I felt hopeful that I would be relieved from isolation precautions and tests for at least a few months. But emerging evidence suggests that re-infection may occur in the short term for new subvariants.
Experts have reduced the protective window of pre-infection from 12 weeks to 28 days. This week, the governments of New South Wales, Western Australia and the Australian Capital Territory all announced that people who have previously had COVID should be tested after 28 days if they experience symptoms. If positive, they are treated as new cases.
Reinfection – testing positive for SARS-CoV-2 (the virus that causes COVID) after recovering from a previous infection – is in progress. Reinfection accounted for 1% of all cases in England in the pre-Omicron period, but in recent weeks it has accounted for more than 25% of daily cases and 18% in New York City.
We do not yet have comparative Australian data, but it may be a similar story given the emergence of the BA.4 and BA.5 Omicron subvariants here. They spread more easily and can cause progression in those who have been previously vaccinated or infected.
It is easy to understand our risk of re-infection on an individual level if we break it down into four main factors: the virus, each person’s immune response to past infection, vaccination status, and personal protective measures. We can’t do much about the first two points, but we can take action on the latter two.
Much has been written about the immune system evasion properties of Omicron subvariants due to multiple new mutations of the SARS-CoV2 spike protein.
Pre-omicron, infection with one variant of covid (alpha, beta, delta) conferred chronic cross-variant immunity. It also provided effective protection against symptomatic infection.
However, that all changed with the emergence of the Omicron BA.1 subvariant in late 2021, with studies demonstrating reduced cross-protection from prior infection associated with less robust antibody responses.
Fast forward several months, and we’re dealing with early Omicron subvariants (BA.1, BA.2) that don’t necessarily protect against their newer siblings (BA.4, BA.5).
Our response to past infection
How our immune system has dealt with a previous Covid infection can affect future exposures.
We know that immunosuppressed people are at increased risk of reinfection (or relapse from persistent infection).
A large UK Covid infection survey shows that in the general population, people who report no symptoms or have low concentrations of virus on their PCR swabs with their prior infection are more likely to be reinfected than those with symptoms or high viral concentrations.
This suggests that when the body mounts a stronger immune response to the first infection, it builds up a defense against reinfection. Perhaps a thin silver lining for those shivering, coughing and spluttering with Covid!
When Covid vaccinations were introduced in 2021, they provided excellent protection against severe disease (hospitalization or death) and symptomatic infections.
Importantly, protection from severe disease is still present due to our immune system responses against parts of the virus that have not mutated from the original strain. Omicron variants can infect people despite vaccination because the variants have found ways to escape “neutralization” from vaccine antibodies.
A new study shows that six months after a second dose of an mRNA vaccine (such as Pfizer and Moderna), antibody levels against all Omicron subvariants were significantly reduced compared to the original (Wuhan) strain. That is, the vaccine’s ability to protect against infection with subvariants wanes much more quickly than it does against the original strain of the virus.
Antibody levels rose again in all variants two weeks after participants received the booster shot, but BA.4 and BA.5 showed the smallest growth gains. Interestingly in this study (and relevant to our highly immunocompromised population), there were higher antibody levels in both infected and vaccinated subjects. Again, gains are lower for the newer Omicron subvariants.
Much of the discussion of late has been about the immune-evasion prowess of COVID. But don’t forget that the virus needs to enter our respiratory tract to cause re-infection.
SARS-CoV-2 is spread from person to person in the air through respiratory droplets and aerosols and by touching contaminated surfaces.
Transmission can be interrupted by doing all the things we’ve been taught over the past two years – practicing social distancing and wearing a mask (preferably not cloth) when not possible, washing hands regularly, opening windows and improving ventilation by using An air purifier for poorly ventilated spaces. And we can be lonely when we are sick.
A re-infected future?
Although reinfection is common, there are some promising recent data showing that it is rarely associated with severe disease. It also shows that booster shots offer some modest protection.
A few (unlucky) people get reinfected within a short period of time (less than 90 days), which is unusual and appears to be due to being young and largely unvaccinated.
Plans for the rollout of mRNA booster vaccines to target Omicron spike protein mutations offer the promise of regaining some immune control over these variants. It will only be a matter of time before further mutations develop.
The bottom line is that it is difficult to get infected or re-infected with a Covid variant in the years to come.
We can’t do much about the evolution of the virus or our own immune systems, but by staying up-to-date with vaccines we can dramatically reduce the risk of it affecting ourselves (and our loved ones) and disrupting our lives. Following general infection-control practices.
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